( PDF ) Study Guide for Linux System Administration I

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Introduction:

Acknowledgments

The original material was made available by LinuxIT's technical training centre www.linuxit.com.

Many thanks to Andrew Meredith for suggesting the idea in the first place. A special thanks to all

the students who have helped dilute the technical aspects of Linux administration through their

many questions, this has led to the inclusion of more illustrations attempting to introduce concepts

in a userfriendly way. Finally, many thanks to Paul McEnery for the technical advice and for starting

off some of the most difficult chapters such as the ones covering the X server (101), modems (102)

and the Linux kernel (102).

The manual is available online at http://savannah.nongnu.org/projects/lpi-manuals/. Thank you to

the Savannah Volunteers for assessing the project and providing us with the Web space.

History

First release (version 0.0) October 2003. Reviewed by Adrian Thomasset.

Revised January 2004 after review by Andrew Meredith.

Audience

This course is designed as a 3 to 4 days practical course preparing for the LPI 101 exam. It is

recommended that candidates have at least one year experience doing Linux administration

professionally. However for those who are ready for a challenge the training is designed to provide

as much insight and examples as possible to help non specialists understand the basic concepts and

command sets which form the core of Linux computing.

The LPI Certification Program

There are currently two LPI certification levels. The first level LPIC-1 is granted after passing both

exams LPI 101 and LPI 102. Similarly passing the LPI 201 and LPI 202 exams will grant the second

level certification LPIC-2.

There are no pre-requisites for LPI 101 and 102. However the exams for LPIC-2 can only be

attempted once LPIC-1 has been obtained.

Instructor Notice

There are no instructor notes with this manual. The following issues must be considered.

The installation exercises suggest a network installation (prepare floppies + installation server).

The exercises in the device and filesystem sections both assume that a new partition can be created.

Make sure during the installation that a large extended partition with at least 100MB free space is

available after all the partitions have been created.

The following RPM packages are needed for the exercises:

rpm-build

sharutils

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No Guarantee

The manual comes with no guarantee at all.

Resources

www.lpi.org

www.linux-praxis.de

www.lpiforums.com

www.tldp.org

www.fsf.org

www.linuxit.com

Notations

Commands and filenames will appear in the text in bold.

The <> symbols are used to indicate a non optional argument.

The [] symbols are used to indicate an optional argument

Commands that can be typed directly in the shell are highlighted as below

command

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Contents

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Introduction:................................................................................................................................. 6

Acknowledgments.......................................................................................................................................6

History.........................................................................................................................................................6

Installation.................................................................................................................................. 10

1. The Installation CD ..............................................................................................................................10

2. Local Installations.................................................................................................................................11

3. Network Installation..............................................................................................................................11

4. Rescue disk..........................................................................................................................................11

5. Partitioning Schemes............................................................................................................................13

6. Easy Dual Booting ...............................................................................................................................13

8. Exercises..............................................................................................................................................15

Hardware Configuration............................................................................................................ 16

1. Memory Support...................................................................................................................................16

2. Resource Allocation..............................................................................................................................16

3. USB Support.........................................................................................................................................17

4. SCSI Devices........................................................................................................................................18

5. Network cards.......................................................................................................................................18

6. Setting up modems...............................................................................................................................19

7. Printer Configuration.............................................................................................................................20

8. Exercises..............................................................................................................................................22

Managing Devices...................................................................................................................... 23

1. Disks and Partitions..............................................................................................................................23

2. Partitioning Tools:.................................................................................................................................25

3. Bootloaders...........................................................................................................................................27

4. Managed devices..................................................................................................................................28

5. Quotas..................................................................................................................................................29

6. Exercises..............................................................................................................................................31

The Linux Filesystem.................................................................................................................32

1. The Filesystem Structure......................................................................................................................32

2. Formatting and File System Consistency.............................................................................................33

3. Monitoring Disk Usage..........................................................................................................................35

4. File Permissions...................................................................................................................................36

5. Exercises..............................................................................................................................................39

The Command Line.................................................................................................................... 41

1. The interactive shell..............................................................................................................................41

2. Variables...............................................................................................................................................42

3. Input, Output, Redirection.....................................................................................................................43

4. Metacharacters and Quotes................................................................................................................45

5. The Command History..........................................................................................................................47

6. Other Commands.................................................................................................................................47

7. Exercise................................................................................................................................................49

File Management........................................................................................................................ 52

1. Moving around the filesystem...............................................................................................................52

2. Finding Files and Directories................................................................................................................52

3. Handling directories..............................................................................................................................54

4. Using cp and mv...................................................................................................................................54

5. Hard Links and Symbolic Links............................................................................................................55

7. Touching and dd-ing............................................................................................................................56

8. Exercises.............................................................................................................................................58

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Process Management................................................................................................................ 60

1. Viewing running processes...................................................................................................................60

2. Modifying Processes.............................................................................................................................61

3. Processes and the shell........................................................................................................................63

4. Exercises..............................................................................................................................................65

Text Processing..........................................................................................................................66

1. cat the Swiss Army Knife......................................................................................................................66

2. Simple tools..........................................................................................................................................67

3. Manipulating text...................................................................................................................................68

4. Exercises..............................................................................................................................................70

Software Installation.................................................................................................................. 71

1. Introduction...........................................................................................................................................71

2. Static and Shared Libraries ................................................................................................................72

3. Source Distribution Installation.............................................................................................................74

4. The RedHat Package Manager RPM ..................................................................................................75

5. The Alien Tool.......................................................................................................................................78

6. Exercises..............................................................................................................................................79

Advanced Text Manipulation.....................................................................................................80

1. Regular Expressions.............................................................................................................................80

2. The grep family.....................................................................................................................................80

3. Working with grep.................................................................................................................................81

4. egrep and fgrep....................................................................................................................................81

5. The Stream Editor - sed.......................................................................................................................81

6. Exercises..............................................................................................................................................84

Using vi....................................................................................................................................... 85

1. vi Modes................................................................................................................................................85

2. Text Items.............................................................................................................................................85

3. Inserting Text........................................................................................................................................86

4. Deleting Text.........................................................................................................................................86

5. Copy Pasting.........................................................................................................................................86

6. Searching .............................................................................................................................................87

7. Undoing.................................................................................................................................................87

8. Saving...................................................................................................................................................87

9. Exercises..............................................................................................................................................88

The X Environment.....................................................................................................................89

1. Introduction...........................................................................................................................................89

3. Configuring X11R6...............................................................................................................................90

4. Controlling X clients..............................................................................................................................92

5. Starting X..............................................................................................................................................92

6. The Display Manager............................................................................................................................93

7. Troubleshooting X Clients.....................................................................................................................96

8. Choosing a Window Manager..............................................................................................................96

9. Exercises..............................................................................................................................................97

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Installation

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Installation

Rather than discuss a step by step installation we will introduce in this module the installation CD, the

different installation methods and the “rescue mode”.

1. The Installation CD

The various Linux distributions have different names for the directories on the installation CD. The generic

structure of the CDROM is as follows:

Generic Installation CD layout

packages: This directory contains the pre-compiled packages. Here are the associated names for the main

distrubutions:

debian: dist

mandrake: Mandrake

redhat: RedHat

suse: suse

images: This directory contains various “images”. These are special flat files often containing directory

structures. An initial ramdisk (initrd) is an example of an image file. There are different types of images

necessary to:

- boot the installation process

- provide additional kernel modules

- rescue the system

Some of these files can be copied to a floppy disk when the installation is started using floppies rather than

the CDROM. The Linux tool used to do this is dd. There is a tool called rawrite which does the same under

DOS.

The image is a special file which may contain subdirectories (much like an archive file).

Image file structure

Image file

An image file can be mounted on a loop device. If the image file name is called Image then the following

command will allow one to view the content of this file in the /mnt/floppy directory:

mount -o loop /path/to/Image /mnt/floppy

dosutils: this directory contains DOS tools which may be used to prepare a Linux installation such as the

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cdrom

dosutils

images

packages

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Installation

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rawrite.exe tool mentioned above. Another tool is the fips utility which non destructively partions a C:\ drive

in two provided the underlying filesystem type is FAT and not NTFS.

2. Local Installations

The easiest and most common type of installation is a local installation. Most distributions are a CD iso image

with an automatic installation script. On machines with no CD-ROM hardware it is still possible to start an

installation from a floppy.

CD-ROM installation

Change the settings in the BIOS for the computer to boot from CD. The installation is menu driven and allows

for advanced and basic configuration.

Floppy Installation

If for some reason you don't boot using the CD-ROM you will need to create a floppy installation image. This

can happen if the CD is not bootable or you have downloaded a non-iso image of the distribution.

Making a bootable installation disk

dd if=/path/to/<image_name> of=/dev/fd0

on a linux box

rawrite.exe

under Windows (not NT)

For RedHat distributions the installation images are in the images directory. The basic image is boot.img.

Other images are more specialised like bootnet.img or pcmcia.img.

In a Suse distribution the floppy image is in the disks directory and the image is called bootdisk.

3. Network Installation

For a RedHat installation this is only a specialised floppy installation. Make a bootable floppy using the

bootnet.img image:

dd /mnt/cdrom/images/bootnet.img of=/dev/fdo

The first part of the installation is text based and will allow you to setup the network parameters needed. The

rest of the installation can be done via FTP, NFS or HTTP. Protocols that allow a full mount (NFS) allow the

install to be done in graphical mode, while file retrieval protocols (FTP HTTP) allow only text mode.

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Installation

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4. Rescue disk

If a Linux system is corrupt it is possible to boot the computer using a rescue disk. This is a small version of

Linux that will mount a minimal virtual filesystem into memory.

The Linux operating system runs entirely in RAM. The aim is to access the root filesystem on the PC hard

drive. Most rescue disks can determine this automatically. Assuming the root filesystem was found on the

first logical partiton of the computer's first IDE disk (/dev/hda5), the rescue disk script can then mount this

resource on a subdirectory of the filesystem in RAM, say /mnt/system.

Changing perspectives

In this situation we have two root filesystems as depected below. To use the root filesystem on the hard

drive as our top directory we need to change our perspective (change root). The chroot tool does just that:

chroot /mnt/system

Rescue mode

RAM kernel

initrd

root filesystem in RAM root filesystem on PC hard drive

Getting started

Old Method:

1. Make a bootable floppy using the boot.img image file: dd if=boot.img of=/dev/fd0

2. Copy the rescue.img image file to a second floppy: dd if=rescue.img of=/dev/fd0

3. Boot the system using with the boot.img diskette

4. At the LILO prompt type "linux rescue". You should see something like

Insert root file system disk:

5. Insert the rescue.img diskette and press enter

6. The boot process will continue until you get a shell prompt

7. You may still need to determine where the root filesystem is on the hard drive

New Method:

1. Insert the Linux installation disk (Suse, RedHat, Mandrake ...)

2. At the prompt type “linux rescue”

3. Follow the instructions.

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4. The instuction should say where the root filesystem is mounted

5. If the root filesystem is mounted on /mnt/sysimage then enter the following command

chroot /mnt/sysimage

5. Partitioning Schemes

The figure below shows a possible partitioning scheme. The File System layout is a tree of directories and

subdirectories. The physical resources with the data are mounted at specific locations on the file system

called mount points.

The root of the tree structure is called root and is represented by a forward slash “/”. At boot time, the boot

loader is told which device to mount at root. The leaves in this tree structure are subdirectories.

During installation you will partition the hard drive and assign a size and a mount point for each partition.

Fig 2: Mount points on the file system

6. Easy Dual Booting

(This section is not for exam purposes).

If Windows9x/2k is already installed on the system the installation setup will automatically configure LILO for

dual booting.

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Pre-installation:

Before altering the system you should run a defragmentation program over the whole disk. This will make

sure that all the blocks used by Windows are rearranged at the beginning of the disk.

Next, using PartitionMagic or fips, partition the C:\ drive in two. The Windows programs are located at the

beginning and the second half must be large enough to hold a Linux installation.

Notice: The average amount of space needed for a recent Linux distribution is 1GB.

Starting the installation from DOS:

For non-NT systems restart your computer in DOS command mode. If you are installing RedHat then you

can run E:\DOSUTILS\AUTOBOOT.BAT. This will start the installation program. Similarly if you are

installing Suse you can run E:\setup.exe under DOS.

The hard drive from a Windows' perspective:

When running Windows the OS will only see the FAT and NTFS filesystems. The rest of the disk where

Linux is installed will be inaccessible.

The hard drive from a Linux point of view:

When running Linux the Windows partition should be called /dev/hda1 (since it's the first partition on the first

physical disk). By default this partition is not mounted. You can make a directory /dos or /mnt/dos and

mount this partition. The disk partition corresponding to C:\ is then accessible.

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7. Exercises

1. Do a network installation using the ready prepared bootnet.img floppy disk.

(i) Choose “Custom System” installation

(ii) Partition the disk with Disk Druid:

This is a suggestion for a partitioning scheme using about 3GB of hard disk space. If you have more

space available then make /usr larger and consider installing more packages than those suggested in

step (iv)

IMPORTANT: Leave a free partition of at least 100MB. We will need this later!!

/boot 20M

/ 250M

/usr 2300M

/home 50M

/tmp 100M

/var 150M

SWAP 128M (Notice that SWAP is a filesystem type and that no mount point is defined)

(iii) Install LILO on /dev/hda2 or /dev/hda3. In all cases do not use the suggested /dev/hda, which is the

MBR.

We deliberately don't want the installation to boot properly. The bootloader will be fixed in step 2(i)

in rescue mode.

(iv) Packages to install: (the names may vary from one distribution to another)

“Network Support”

“Classic X Window System”

“X Window System”

“Software Development” [This is important, we will need this to compile packages later]

(v) Don’t create a bootable floppy

2. Rescue the system:

(i) Reboot with the bootnet.img floppy disk (or the installation CDROM of you have it). This time type

linux rescue

at the prompt.

(ii) Read all the instructions until you get to a prompt. Use the chroot command as suggested.

(iii) Edit /etc/lilo.conf (use vi). You should have

boot=/dev/fd0

prompt

linear

timeout=50

image=/boot/vmlinuz-<kernel-version>

label=linux

read-only

root=/dev/<root-partition>

(v) Run /sbin/lilo. If an error occurs you may have to replace linear by lba32 depending on your disk.

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Hardware Configuration

1. Memory Support

The system’s RAM is first detected by the BIOS. All types of RAM (EDO, DRAM and SDRAM) are

recognised by the Linux kernel. There can be problems with old hardware when the BIOS cannot detect

64MB of RAM or more. In this case one needs to passe parameters to the kernel at boot time.

When using LILO insert the following into /etc/lilo.conf:

append=”mem=<amount of ram>M”

Remember to run /sbin/lilo.

If you are using GRUB add the following to /etc/grub.conf on the line beginning with kernel :

kernel vmlinuz mem=<amount of ram>M

2. Resource Allocation

To allow peripherals and devices on the PC to communicate directly with system resources, in particular

the CPU, the system allocates resources such as lines and channels for each device. These resources

are Interrupt Request Lines (IRQ), Input/Output addresses and Direct Memory Access channels (DMA).

IRQs: The Interrupt Request Lines allow devices to request CPU time. The CPU will stop its current

activity and process the instructions sent by the device. IRQs range from 0 to 15.

I/O address: These represent specific addresses in the system’s memory map. The CPU will then

communicate with the device by reading and writing to memory at the specified address.

DMA: Certain devices can access the system’s memory through a DMA channel, allowing them to write

and process data without accessing the CPU. This can enhance performance.

● Listing Allocated Resources

The kernel keeps information related to allocated resources in the /proc directory. The relevant files are:

/proc/dma

/proc/interrupts

/proc/ioports

/proc/pci

Allocated resources can also be listed using tools such as lspci and dmesg:

lspci: lists chipset information of all attached PCI components. Lists I/O and IRQ settings with the -v flag .

Also notice the -b (BUS centric) option which shows allocations assigned by the BIOS rather than the

kernel.

dmesg. This displays the kernel messages logged at boot time. The kernel scans all the hardware on the

system and can automatically allocate modules (drivers) for given chipsets. These messages are also

available in /var/log/dmesg.

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● Typical Resources

Device

I/O port IRQ

/dev/ttyS0 0x03f8 4

/dev/ttyS1 0x02f8 3

/dev/lp0 0x378 7

/dev/lp1 0x278 5

soundcard 0x220

● Manual Resourse Allocation

NOTICE:

This is a very common example, however since kernel modules are only discussed in LPI 102 some may

find it difficult. You may skip this example and go to § 3

Example: configuring two ethernet cards

1. For statically compiled modules, parameters can be passed to the kernel at boot time. A typical

example is when two ethernet cards are present and only the first one is detected. The following line tells

the kernel that:

- there is an ethernet card using IRQ 10 and I/O 0x300

- there is another ethernet card using IRQ 9 and I/O 0x340

ether=10,0x300,eth0 ether=9,0x340,eth1

You type this line at the LILO/GRUB ‘boot:’ prompt, or else, as with the RAM settings before, edit

/etc/lilo.conf (use an append= statement) or /etc/grub.conf.

Notice that the ether= statement is a generic kernel command similar to root=, mem= or init=.

Also notice that you need not specify any information about the ethernet card (Intel, Netgear ...)

2. For dynamically compiled modules, IRQ and I/O address settings can be defined using /

etc/modules.conf (or /etc/conf.modules). Assuming that in the above example both cards where using

the e100.o kernel module, then /etc/modules.conf would contain the following:

alias eth0 e100

alias eth1 e100

options eth0 io=0x300 irq=10

options eth1 io=0x340 irq=9

3. USB Support

The Universal Serial Bus (USB) is a communication architecture designed to connect devices to a PC.

These devices are divided into four classes:

Display Devices

Communication Devices

Audio Devices

Mass Storage Devices

Human Interface Devices (HID)

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The devices are plugged into a USB port which is driven by a USB controller. Support for USB controllers

is present in the Linux kernel since version 2.2.7 ( The Linux USB sub-system HOWTO)

There are 3 types of USB host controllers:

Host Controler Kernel Module

OHCI (Compaq) usb-ohci.o

UHCI (Intel) usb-uhci.o

EHCI (USB v 2.0) ehci-hdc.o

4. SCSI Devices

Types of SCSI devices

There are two types of SCSI interfaces:

- an 8-bit interface with a bus that supports 8 devices, this includes the controller, so there is only space

for 7 block devices (tapes, disks, etc)

- a 16-bit interface (WIDE) with a bus that supports 16 devices including the controller, so there can only

be 15 block devices.

Each device is assigned a unique SCSI ID that can be set using jumpers on the disk. The IDs range from

0 to 7 for 8-bit controllers and from 0 to 15 for 16-bit controllers.

Logical units

The Logical Unit Number (LUN) is used to differentiate between devices within a SCSI target number.

This is used, for example, to indicate a particular partition within a disk drive or a particular tape drive

within a multi-drive tape robot. It is not seen so often these days as host adapters are now less costly and

can accommodate more targets per bus.

Booting SCSI disks

The system will boot from the device with SCSI ID 0 by default. This can be changed in the SCSI BIOS at

boot time.

5. Network cards

● The Network Interface

The network interface card (NIC) must be supported by the kernel. You can get information about your

current card using either of the following:

dmesg, lspci, scanpci, /proc/interrupts, /sbin/lsmod.or /etc/modules.conf:

dmesg

► Linux Tulip driver cersion 0.9.14 (February 20, 2001)

PCI: Enabled device 00:0f.0 (0004 ->0007)

PCI: Found IRQ 10 for device 00:0f.0

eth0: Lite-On 82cl68 PNIC rev 32 at 0xf800, 00:0A:CC:D3:6E:0F,

IRQ 10

eth0: MII transceiver #1 config 3000 status 7829 advertising

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cat /proc/interrupts

► 0: 8729602 XT-PIC timer

1: 4 XT-PIC keyboard

2: 0 XT-PIC cascade

7: 0 XT-PIC parport0

8: 1 XT-PIC rtc

10: 622417 XT-PIC eth0

11: 0 XT-PIC usb-uhci

14: 143040 XT-PIC ide0

15: 180 XT-PIC ide1

/sbin/lsmod

► Module Size Used by

tulip 37360 1 (autoclean)

From the examples above we see that the Ethernet card’s chipset is Tulip, the i/o address is 0xf800 and

the IRQ is 10. This information can be used either if the wrong module is being used or if the resources

(i/o or IRQ) are conflicting.

This information can either be used to insert a module with a different i/o address (using the modprobe or

insmod utilities) or can be saved in /etc/modules.conf (this will save the settings for the next bootup).

6. Setting up modems

● The Modem device

We will only consider serial modems. The following table shows the equivalence between DOS COM

ports and Linux serial devices.

Table 1: Serial port equivalence DOS-Linux

DOS

Linux

COM1 /dev/ttyS0

COM2 /dev/ttyS1

COM3 /dev/ttyS2

Most Linux distributions have hardware browser tools (GUIs) which can detect modems. But one can also

use setserial to scan the serial devices. With the -g option this utility will tell you which serial devices are

in use:

setserial -g /dev/ttyS*

► /dev/ttyS0, UART: 16550A, Port: 0x03f8, IRQ: 4

/dev/ttyS1, UART: 16550A, Port: 0x02f8, IRQ: 3

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A symbolic link called /dev/modem pointing to used serial portcan be used to reference the modem.

Manually linking the modem device

ln -s /dev/ttyS1 /dev/modem

The setserial tool is also used to set the speed of the serial port.

● Dialup Configuration (The LPI101 objectives only cover hardware detection and not configuration)

The wvdial commandline tool has a setup script called wvdialconf which will scan the system for

modems (all serial and USB ports are scanned). Once the script has run a skeleton configuration file is

generated as below:

Sample /etc/wvdial.conf file:

[Dialer Defaults]

Modem = /dev/ttyS1

Baud = 115200

Init1 = ATZ

Init2 = ATQ0 V1 E1 S0=0 &C1 &D2 S11=55 +FCLASS=0

; Phone = <Target Phone Number>

; Username = <Your Login Name>

; Password = <Your Password>

A quick way to get started is to replace Defaults with the name of your provider say WorldISP, fill in the

Usernam/Password entries and type the following:

wvdial WorldISP

7. Printer Configuration

Printing is covered in depth in LPI 102. From a hardware perspective, the printers are detected at boot

time automatically and can be seen in the dmesg output.

Linux printing happens in two stages. First the raw data is filtered into a postscript format, then the printing

itself is handled by the ghostscript, or gs utility.

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Using printtool (not examined)

This utility creates an entry in /etc/printcap. The main features which need to be specified are the location

of the input_filter=if, the spool_directory=sd and the printer_device=lp.

If the printtool fails to detect which parallel port corresponds to the printer device you can use the dmesg

utility to recall the kernel's initial parallel port scan.

Here is an example of a system with a local printer plugged into the first parallel port /dev/lp0

Parallel port scan at the end of dmesg

parport0: PC-style at 0x378 (0x778) [SPP,ECP,ECPEPP,ECPPS2]

parport0: detected irq 7; use procfs to enable interrupt-driven operation.

parport_probe: succeeded

parport0: Printer, HEWLETT-PACKARD DESKJET 610C

lp0: using parport0 (polling)

Sample /etc/printcap file

# This file can be edited with the printtool in the control-panel.

##PRINTTOOL3## LOCAL cdj550 300x300 a4 {} DeskJet550 3 {}

lp:\

:sd=/var/spool/lpd/lp:\

:mx#0:\

:sh:\

:lp=/dev/lp0:\

:if=/var/spool/lpd/lp/filter:

Figure 7: The gtk-based printtool GUI

Using cups

Cups is a newer administration and configuration tool for printers. It's main configuration files are stored in

/etc/cups. The printing process is the same except that cups uses its own filters situated in /

usr/lib/cups.

The configuration tool for CUPS is a Web based GUI running on port 631.

 When using cups lpd is replaced by the cupsd daemon.

NOTICE

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A local printer is physically detected at boot time for both USB and parallel connections.

Information on the boot process is displayed at any time with dmesg

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8. Exercises

1. Use the dmesg command to view the /var/log/dmesg file. Search for keywords such as USB, tty

or ETH0.

- What are the names of the USB controllers used?

- What are the IRQs for the first two serial ports?

2. Investigate the contents of the following files:

/proc/ioports

/proc/interrupts

/proc/pci

/proc/dma

3. The PCI bus:

- Investigate the output of lspci -v and scanpci –v. What type of ethernet card in

present?

- Verify that there are as many ‘bus ’ entries in /proc/pci. Does this file give as much

information as the commands above?

4. USB tools:

- Use lsmod and lsusb to determine which type of host controller is used on your

system, UHCI, OHCI or EHCI (for USB v 2.0).

- Use usbmodules to list the kernel module which can handle the plugged in interface.

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Managing Devices

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Managing Devices

1. Disks and Partitions

Physical disks:

On a running Linux system, disks are represented by entries in the /dev directory. The kernel

communicates with devices using a unique major/minor pair combination. All major numbers

are listed in /proc/devices. For example the first IDE controller‘s major number is 3:

Block devices:

1 ramdisk

2 fd

3 ide0

Hard disk descriptors in /dev begin with hd (IDE) or sd (SCSI), a SCSI tape would be st, and

so on. Since a system can have more than one block device, an additional letter is added to

the descriptor to indicate which device is considered.

Table 1 Physical block devices

hda

Primary Master

hdb

Primary Slave

hdc

Secondary Master

hdd

Secondary Slave

sda

First SCSI disk

sdb

Second SCSI disk

NB Inserting a new SCSI hard drive with a target number between two existing drives will

bump up the device letter of the higher numbered drive. This can cause chaos within a disk

system.

Disk Partitions:

Disks can further be partitioned. To keep track of the partitions a number is added at the end of

each physical device.

Table 2 Partitions

hda1

First partition on first hard disk

hda2

Second partition on first hard disk

sdc3

Third partition on third SCSI disk

IDE type disks allow 4 primary partitions, one of which can be extended. The extended

partition can further be divided into logical partitions. There can be a maximum of 64 partitions

on an IDE disk and 16 on a SCSI disk.

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Example 1: The primary partitions (1,2,3,4) and (1,2,5,6,7,8)

Typical output of fdisk -l

Device Boot Start End Blocks Id System

/dev/hda1 * 1 748 6297448+ b Win95 FAT32

/dev/hda2 785 788 32130 83 Linux

/dev/hda3 789 2432 13205430 5 Extended

/dev/hda5 789 1235 3590496 83 Linux

/dev/hda6 1236 1618 3076416 83 Linux

/dev/hda7 1619 1720 819283+ 83 Linux

/dev/hda8 1721 1784 514048+ 83 Linux

/dev/hda9 1785 1835 409626 83 Linux

/dev/hda10 1836 1874 313236 83 Linux

/dev/hda11 1875 1883 72261 82 Linux swap

On this system the main feature to notice is that there are 3 primary partitions. The third

partition is extended (/dev/hda3) and holds 8 logical partitions. The primary partition /dev/hda3

is not used. In fact /dev/hda3 acts as a 'container' and a filesystem exists only on the enclosed

logical partitions.

NOTICE

Make sure to distinguish between primary, extended and logical partitions. Also make sure

you understand the naming convention for the IDE disks and controllers.

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2. Partitioning Tools:

1. Before installation: (not for exam purpose)

PartitionMagic

fips

Notice that fips only handles fat16 and fat32. On the other hand, PartitionMagic is much more

versatile and can handle most common UNIX formats as well.

No partitioning is needed if for example C:\ and D:\ exist and the D:\ drive is empty.

Partitioning before installation:

2. During installation: (not for exam purpose)

During the installation process the Linux partition is partitioned again. Why do Linux systems require

further partitioning? To answer this question we first define mount points.

Defining a mount point: (also see figure page5)

One has the choice to associate a piece of hardware (or resource) to a directory. For example

the root directory “/” which is more or less like the C:\ drive for DOS could correspond to the /

dev/hda2 partition, and the subdirectory /boot could correspond to the partition /dev/hda3.

“/dev/hda3 is said to be mounted on /boot”. The directory on which a block device is

mounted is then called a mount point.

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While installing Linux you will have the choice of creating new partitions and associating each

partition to a mount point.

For advanced users this is done in two steps:

1. Use the fdisk tool to create new partitions

2. Associate a mount point to each partition

For intermediate users most distributions include a userfriendly tool that does both these steps

at once:

diskdrake (Mandrake)

DiskDruid (RedHat)

The very early success of RedHat over other projects such as Debian was the introduction of

intuitive installation tools such as DiskDruid.

Finally, for beginners and busy sysadmin’s, the latest Linux distributions will automatically

assign a partition scheme.

3. On a Running System:

Once the operating system is installed you can use the fdisk utility to configure new partitions.

We will next look at the basic syntax for fdisk

Example:

1) Start partitioning the first hard drive:

fdisk /dev/hda

2) Type m for help. Then create a new partition with n.

3) To write the changes to disk type w.

4) REBOOT.

These four points outline the steps you would follow to create new partitions. The last point

is often overlooked. This forces the partition table in the master boot record MBR to be reread.

NOTICE

You need to create a filesystem on a new partition with mkfs or mke2fs before using it

This ends the survey of available partitioning tools. We next take a look at bootloaders.

3. Bootloaders

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The MBR occupies the first sector of the disk (512 bytes) and contains the partition tables

together with a bootloader. At boot time the bootloader reads the partition tables looking for a

partition marked “active” and loads the first sector of this partion.

LILO the Linux Bootloader

There are roughly 3 parts envolved:

1. LILO

This is the loader itself. LILO is installed on the MBR and loads the second stage bootloader,

generally situated in /boot/boot.b.

2. /etc/lilo.conf

The main options are specified here

boot* where LILO should be installed (/dev/hda is the MBR)

install which second stage to install (boot.b is the default)

prompt give the user a chance to choose an OS to boot

default name of the image that will be booted by default

timeout used with prompt, causes LILO to pause (units are 1/10 of a sec)

image* path to the kernel to boot (one can use ‘other’ to chain load)

label* name of the image. This is the name a user can type at the boot prompt

root* the name of the disk device which contains the root filesystem /

read-only* mount the root filesystem read-only for fsck to work properly

append give kernel parameters for modules that are statically compiled.

linear/lba32 these options are mutually exclusive. Both ask LILO to read the disk

using

Linear Block Addressing. linear is typically used for very large disks.

Lba32 is used to allow boot time access to data beyond the first 1024 cylinders.

3. /sbin/lilo

This binary reads it’s configuration file /etc/lilo.conf and installs the LILO bootloader.

/sbin/lilo should be run every time a change is made to /etc/lilo.conf

GRUB the Grand Unified Bootloader

GRUB is also installed on the MBR. You can either alter this MBR with the /sbin/grub shell or

use a configuration file called /boot/grub/grub.conf which will be read by /sbin/grub-install

Detailed information about GRUB can be found in the info pages

GRUB keywords (used in /boot/grub/grub.conf):

1. General/Global

default image that will boot by default (the first entry is 0)

timeout prompt timeout in seconds

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2. Image

title name of the image

root where the 2

stage bootloader and kernel are e.g (hd0,0) is /dev/hda

kernel path for the kernel starting from the previous root e.g /vmlinuz

ro read-only

root the filesystem root

Example grub.conf

default=0

timeout=10

splashimage=(hd0,0)/grub/splash.xpm.gz

title Linux (2.4.18-14)

root (hd0,0)

kernel /vmlinuz-2.4.18-14 ro root=/dev/hda5

initrd /initrd-2.4.18-14.img

4. Managed devices

At boot time the /etc/fstab file assigns mount points for block devices.

The /etc/fstab format

device mount-point fstype options dump-number fsck-number

Sample /etc/fstab

LABEL=/ / ext2 defaults 1 1

LABEL=/boot /boot ext2 defaults 1 2

LABEL=/home /home ext3 defaults 1 2

/dev/fd0 /mnt/floppy auto noauto,owner 0 0

LABEL=/usr /usr ext2 defaults 1 2

LABEL=/var /var ext3 defaults 1 2

none /proc proc defaults 0 0

none /dev/shm tmpfs defaults 0 0

none /dev/pts devpts gid=5,mode=620 0 0

/dev/hdc9 swap,pri=-1 swap defaults 0 0

/dev/cdrom /mnt/cdrom iso9660 noauto,owner,kudzu,ro 0 0

On a running system the /etc/fstab file also acts as a shortcut for assigning a resource to a

specific directory. For example:

mount /dev/cdrom

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The mount utility reads fstab and deduces where to mount the resource. Notice that some of

the devices are accessed using a label. Labels are assigned to devices with the tune2fs tool:

tune2fs -L /usr/local /dev/hdb12

Option summary for mount:

rw,ro

read-write and read-only

users

the device can be read and unmounted by all users

user

the device can unmounted only by the user

owner

the device will change it's permission and belong to the user that mounted it

usrquota

start user quotas on the device

grpquota

start group quotas on the device

NOTICE

Remember that mount -a will mount all filesytems in /etc/fstab that have not been

mounted and do not have the option noauto

5. Quotas

The quota tools allow administrators to set up quotas without having to reboot. Here are the

steps.

1. Edit /etc/fstab and add usrquota to the options

2. Remount the partition:

mount -o remount <device>

3. Start the quota stats:

quotacheck -ca

The preliminary aquota.user file is generated at the top of the directory.

4. Edit quotas for each user:

edquota -u <user>

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Here a soft/hard limit must be set for both the number of blocks and inodes available for each

user.

The system will allow the user to exceed the soft limit during a certain grace period.

After the grace period has expired the soft limit will be enforced as a hard limit.

5. START enforcing quotas:

quotaon –a

Users can query the quota status with quota. The system administrator can generate reports

with repquota or quotastats.

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6. Exercises

1. Create 1 new partition on the /dev/hda device using fdisk.

fdisk /dev/hda

HINT: To create a new partition type n. The partition type defaults to 83 (Linux)

To write the new partition table type w.

The partition table needs to be read: REBOOT the computer !

2. Make a new filesystem (format) on one of the partitions:

mkfs <device>

3. (i) Make a directory called data in the root directory.

mkdir /data

(ii) Edit /etc/fstab and allocate the mount point /data to this new resource

<device> /data ext2 defaults 0 2

4. Force mount to read /etc/fstab:

mount –a

If this doesn't work check that each entry is correct in the fstab and make sure that the

directory /data exists (2 (i))

5. Follow the steps in this chapter to enforce quotas on this device.

After step (2) run the mount command and look at the output. Which option from

/etc/fstab can be seen showing that quotas are availabe on the device? _________

After step (3) which file is created in the /data directory? __________

Before testing quotas for with non-root users, add read-write permissions on /data

chmod o+rw /data

In extreme cases it may be easier to reboot and let the init scripts build the aquota.user

(or aquota.group) file. If nothing is showing with the quotas, repquota, or quotastats

tools make sure you have read-write access for everyone on /data [chmod a+rw /data ]

6. (OPTIONAL) The instructor computer has a NFS share. Find out which directory is

shared and edit /etc/fstab to mount this share on /mnt/nfs. Use the noauto option fot

the share not to mount at boot time.

7. SWAPPING bootloaders

a. Uninstall LILO from the MBR (or the floppy)

lilo –u

b. Modify the grub.conf sample on p. 28 to reflect your system

c. Install GRUB on the floppy with grub-install /dev/fd0

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The Linux Filesystem

1. The Filesystem Structure

A filesystem is similar to a tree structure. The root of the tree is represented at the top and the leaves below.

As mentioned earlier, once partitions have been created each partition must be given a mount point. This is

typically done at installation time. To help us understand where things are kept, let us look at the Linux file

system hierarchy.

The top of a Linux file system hierarchy starts at root (/). This is similar to C:\ under DOS except that C:\ is

also the first device, whereas the root directory can be mounted anywhere.

Figure 1: The base directories

The base directories are the first subdirectories under the root directory. These are installed by an rpm

package usually called filesystem.

rpm -ql filesystem

During the booting process the kernel first mounts the root (/) partition. In order to mount and check any

further partitions and filesystems a certain number of programs such as fsck, insmod or mount must be

available.

 The directories /dev, /bin, /sbin, /etc and /lib must be subdirectories of root (/) and not mounted on

separate partitions.

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Base directories:

• /bin and /sbin

Contain binaries needed to boot up the system and essential commands.

• /dev

Location for device or special files

• /etc

Host specific configuration files

• /lib

Shared libraries for binaries in /bin and /sbin. Also contains kernel modules

• /mnt/ or /media (Suse)

Mount point for external filesystems

• /proc

Kernel information. Read-only except for /proc/sys/

• /boot

Contains the Linux kernel, the system maps and the “second stage” bootloaders.

• /home (optional)

The directories for users. Initially contains the contents from /etc/skel/

• /root (optional)

The directory for user root

• /tmp

Temporary files

• /usr

User Specific Resource. Mainly static and shareable content

• /usr/local or /opt (optional)

Add-on software applications. Can also contain shared libraries for add-on software.

• /var/www, /var/ftp/ or /srv (Suse)

Location for HTML pages and anonymous FTP directories.

• /var

Variable data, such as spools and logs. Contains both shareable (eg. /var/spool/mail) and non-

shareable (eg. /var/log/) subdirectories.

2. Formatting and File System Consistency

In order to organise data on a disk partition one needs to create a file system. At installation time you will be

asked which type of file system must be used.

Many file system types are supported. The ext2 file system type is the default and is also known as “Linux

Native”. In some more recent installers, ext3 is the default. This is really only an ext2 filesystem with a journal

patched on top.

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A different file system type must be used for SWAP. The file system for Swap is of type swap and cannot be

anything else.

The Second Extended File System

Lets take a closer look at the ext2 (second extended) file system. The ext2 consists of blocks of size 1024

bytes =1 KB (default). Without entering into too much detail, there are three types of blocks:

● Superblocks:

Repeated every 8193 blocks. Contains information about block-size, free inodes, last mounted time, etc …

● Inodes:

Contains pointers to data blocks. The first 12 blocks of data are directly accessed. If the data exceeds 12KB,

then indirect inodes act as relays.

Each inode is 256 bytes and contains the user, group, permissions and time stamp of the associated data.

● Data Blocks:

These are either files or directories and contain the actual data.

Formatting tools

The file systems supported by the kernel allow one to read from a pre-formatted disk. To create these file

systems while running a Linux system one also needs to install the associated formatting tools.

The formatting tool for ext2 is mkfs.ext2 or mke2fs. Similarly the formatting tool for the xfs file system type

from Silicon Graphics will be mkfs.xfs and may have to be installed separately.

The mkfs tool acts as a front for all these file system types. The syntax is:

mkfs –t <fstype>

Notice that the ext3 is an ext2 file system type on which a journaling system has been added (see the

exercises for details).

Example 1: Making a jfs filesystem

mkfs –t jfs /dev/hda12

Example 2: Making a ext2 filesystem

mke2fs /dev/hda11 [or mkfs –t ext2 /dev/hda11]

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File System Consistancy

If the file system is damaged or corrupt, then the fsck utility should be run against the partition (the minimum

requirement is that the file system be unmounted or mounted read-only).

fsck acts as a front that automatically detects the file system type of a partition. Then as with mkfs, the tools

fsck.ext2, fsck.ext3 will be named accordingly.

You can explicitly specify a file system type with the following syntax:

fsck –t <fstype> <device>

Example: Checking a reiserfs filesystem on the /dev/sdb10 device:

fsck –t reiserfs /dev/sdb10

fsck.reiserfs /dev/sdb10

3. Monitoring Disk Usage

Using mount and df :

Both these tools work on a device level, as opposed to a directory level. The mount and umount tools

maintain the list of mounted filesystems in /etc/mtab.

Typing mount with no options will show all filesystems currently mounted. The output is similar to /etc/mtab.

Notice that the kernel also keeps track of mounted filesystems in /proc/mount.

In addition to showing all mounted devices the df tool will also show Used and Available disk space. By

default this is given in blocks of 1K.

df -h

➔

Filesystem Size Used Avail Use% Mounted on

/dev/hda9 289M 254M 20M 93% /

/dev/hda2 23M 7.5M 14M 35% /boot

none 62M 0 61M 0% /dev/shm

/dev/hda5 1.4G 181M 1.1G 13% /share

/dev/hda7 787M 79M 669M 11% /tmp

/dev/hda3 4.3G 3.4G 813M 81% /usr

/dev/hda6 787M 121M 627M 17% /var

//192.168.123.2/share 12G 8.8G 3.7G 71% /mnt/smb

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Using du :

This tool will display disk usage. This is done on a per directory basis. Notice that du cannot display available

space since this information is only available at a device level.

4. File Permissions

Changing permissions and owners

From the previous figure we see that permissions can be acted upon with chmod. There are 3 categories of

ownership for each file and directory:

The symbolic values for the owner fields:

u: a valid user with an entry in /etc/passwd

g: a valid group with an entry in /etc/group

o: other

Example:

-rw-rw-r-- 1 jade sales 24880 Oct 25 17:28 libcgic.a

Changing Permissions:

chmod g=r,o-r libcgic.a

chmod g+w libcgic.a

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Changing user and group:

chown root libcgic.a

chgrp apache libcgic.a

NOTICE

A useful option for chmod, chown and chgrp is –R which recursively changes

ownership and permissions through all files and directories indicated.

Symbolic and octal notation

Permissions can be read=r, write=w and execute=x. The octal values of these permissions are listed in the

next table.

Table 2: Octal and symbolic permissions.

Symolic octal

write 2

execute 1

Permissions apply to the user, the group and to others. An item has a set of 3 grouped permissions for each

of these categories.

Table 3: How to read a 755 or -rwxr-xr-x permission

user group other

rwx

4+2+1=7

r_x

4+1=5

r_x

4+1=5

The standard permission

UNIX system create files and directories with standard permissions as follows:

Standard permission for:

Files 666 -rw-rw-rw-

Directories 777 -rwxrwxrwx

Umask

Every user has a defined umask that alters the standard permissions. The umask has an octal value and is

subtracted(*) from the octal standard permissions to give the files permission (this permission doesn't have a

name and could be called the file's effective permission).

(*) While subtraction works in most cases, it should be noted that technically the standard permissions and

the umask are combined as follows:

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Final Permissions = Standard Permissions (logical AND) (NOT)Umask

On systems where users belong to separate groups, the umask can have a value of 002.

For systems which place all users in the users group, the umask is likely to be 022.

SUID permissions

It is possible for root to give users permission to execute programs they would usually be unable to. This

permission is the SUID permission with a symbolic value s or a numerical value 4000.

For example root can write a C shell script that executes a program and set the SUID of the script with

chmod 4777 script or chmod u+s script. (NB Bourne and Bash scripts do not honour SUID bits set on the

script files.)

Examples:

chmod 4755 /bin/cat

chmod u+s /bin/grep

SGID permissions

The SGID is a similar permission set for group members. The symbolic value is s and the octal value of

2000.

Setting SGID on a directory changes the group ownership used for files subsequently created in that directory

to the directories group ownership. No need to use newgrp to change the effective group of the process

prior to file creation.

Examples:

chmod 2755 /home/data

chmod g+s /bin/wc

The sticky bit

The sticky bit permission with value 1000 has the following effect:

- Applied to a directory it prevents users from deleting files unless they are the owner (ideal for

directories shared by a group)

- Applied to a file this used to cause the file or executable to be loaded into memory and caused later

access or execution to be faster. The symbolic value for an executable file is t while for a non

executable file this is T. As file system caching is more generic and faster, file sticky bits tend not be

supported any more.

Examples:

chmod 1666 /data/store.txt

chmod o+t /bin/bash

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5. Exercises

Filesystem

1. Create 2 new partitions (larger than 50M) on the /dev/hda device using fdisk.

HINT: To create a new partition type n. The partition type defaults to 83 (Linux)

To write the new partition table type w.

The partition table needs to be read: REBOOT the computer !

2. Format the first partition using the ext2 filesystem type and the second with reiserfs.

HINT: The mkfs tool is a front for mkfs.ext2 or mkfs.reiserfs, etc. The syntax is

mkfs –t <fstype> <device>

3. Make directories in /mnt and mount the new partitions

mkdir /mnt/ext2

mkdir /mnt/reiserfs

4. Check the status of your system:

Use mount to verify which devices are mounted. The permissions set in fstab are visible too.

Use df to check the total number of blocks used. The –k option will convert the number of blocks in

kilobytes (the default block size for ext2)

Run fsck on one of the newly created filesystems. The fsck utility is a front for fsck.ext2, fsck.ext3,

fsck.reiserfs, etc. The syntax is:

fsck <device>

5. Going further: Changing from ext2 to ext3 :

Notice that there are no tools to create ext3 formated partitions. In fact the ext3 format is the same

as the ext2 format with a journal added. These are the steps:

mke2fs /dev/hda10

tune2fs –j /dev/hda10

At this stage the system has added a journal to the /dev/hda10 partition, making it an ext3 formated

partition. This process is non-destructive and reversible. If you mount an ext3 as an ext2 filesystem, the .

journal file will be erased. You can add it again with tune2fs …

File permissions

1. Login as a user (non root). Create a file using touch and verify that it has the effective permission

664.

2. Change the umask to 027. If you create a new file what is it’s effective permission? _________

Where is the value of umask set? Depening the systems this can be /etc/profile or /etc/bashrc

3. Add 2 users to your system.

useradd user1

useradd user2

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Add passords with passwd user1 and passwd user2

4. Create a group called sales.

groupadd sales

5. Add the users to the group sales

gpasswd -a user1 sales

gpasswd -a user2 sales

6. Create a directory /news owned by the group sales and read-writable for this group.

mkdir -m 770 /news ; chown .sales /news

7. Set the GID to the /news directory.

chmod g+s /news

What are the symbolic permissions (eg. -rwxr_xr_x) on /news? [use ls -ld /news ] ______

Verify that a group member doesn’t need to type “newgrp sales” in order to create files with the right

permissions. Can members of the group sales modify any files in this directory?

8. Add the sticky-bit permission on the /news directory. Verify that only user-owners can modify the files

in the that directory. What are the permissions like on /news? ______________

10. As root set SUID root xeyes. Login as a non root user. Check that this binary runs with UI root.

chmod u+s `which xeyes`

ps aux | grep xeyes

(the binary should be running as root)

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The Command Line

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The Command Line

Overview

A basic way to interact with a computer system is to use the command line. The shell interprets

the instructions typed in at the keyboard. The shell prompt (ending with $ or # for user root)

indicates that it is ready for user input.

The shell is also a programming environment which can be used to perform automated tasks.

Shell programs are called scripts.

Most Common shells

The Bourne shell /bin/sh

The Bourne again

shell

/bin/bash

The Korn shell /bin/ksh

The C shell /bin/csh

Tom's C shell /bin/tcsh

Since the bash shell is one of the most widely used shells in the Linux world the LPI

concentrates mainly on this shell.

1. The interactive shell

Shell commands are often of the form

command [options] {arguments}.

Printing text to the screen

The the bash shell uses the echo command to print text to the screen.

echo “this is a short line”

Full/Relative path

The shell interprets the first ¨word¨ of any string given on the command line as a command. If the string

is a full or relative path to an executable then the executable is started. If the first word has no ¨/¨

characters, thenthe shell will scan directories defined in the PATH variable and attempt to run the first

command matching the string.

For example if the PATH variable only contains the directories /bin and /usr/bin then the string xeyes

won't be found since it is stored in /usr/X11R6/bin/xeyes so the full path needs to be run

/usr/X11R6/bin/xeyes

An alternative to typing the full path to an executable is to use a relative path. For example, if the user is

in the directory where the xeyes program is stored then one can type

./xeyes

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2. Variables

Shell variables are similar to variables used in any computing language. Variable names are limited to

alphanumeric characters. For example CREDIT=300 simply assigns the value 300 to the variable named

CREDIT.

1. initialise a variable: Variable-Name=value (no spaces !!)

2. reference a variable: $Variable-Name

CREDIT=300

echo $CREDIT

Export, Set and Env:

There are two types of variable: local and exported.

Local variables will be accessible only to the current shell. On the other hand, exported variables are

accessible by both the shell and any child process started from that shell.

The commands set and env are used to list defined variables

The set and env commands

set

Lists all variables

env

Lists all exported variables

A global variable is global in the sense that any child process can reference it.

LOCAL EXPORTED

Example: Make the CREDIT variable a global variable. Test whether it's listed with set or env.

export CREDIT

env | grep CREDIT

Start a new shell (child process) and verify that CREDIT is accessible. Can one start any shell and be

sure that CREDIT is still declared ?

Table 1.2 List of common predefined variables

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VAR=val

VAR = ??

parent

child

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VAR = val

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PREDEFINED VARIABLES

MEANING

DISPLAY Used by X to identify where to run a client application

HISTFILE Path to the users .bash_history file

HOME The path to the user's home

LOGNAME The name used by the user to log in

PATH List of directories searched by the shell for programs to be

executed when a command is entered without a path.

PWD The current working directory

SHELL The shell used (bash in most Linux distributions)

TERM The current terminal emulation

Special variables

The next few variables are related to process management.

$! represents the PID value of the last child process

$$ represents the PID of the running shell

$? is 0 if the last command was executed successfully and 1 otherwise

3. Input, Output, Redirection

UNIX processes normally open three standard file descriptors which enable it to process input and

output. These standard descriptors can be redefined for any given process. In most cases the stdin

descriptor is the keyboard, and the two output descriptors, stdout and stderr, is the screen.

A process and it’s 3 descriptors

Numerical values for stdin, stderr and stdout

stdin

stdout

stderr

stdout redirection

program > file

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The data flows from left to right.

fdisk –l > partions.txt

This will run the fdisk utility and output the result to the partitions.txt file. No output is visible. Also notice

that the shell will read this line from the right. As a result, the

partitions.txt file will be created first if it doesn’t exist and overwritten if the ‘>’ operator is used.

The ‘>>’ operator will append output to a file.

STDOUT Redirection

stdin redirection

program < file

In this case data flows from right to left. The ‘<’ operator is only used for stdin and cannot be used for

stdout.

If the file instuctions contains on each line the letters p, m, and q then the next example would cause

fdisk to print the partition table of /dev/hda, print the utility’s help screen and finally quit:

fdisk /dev/hda < instructions

STDIN Redirection

stderr redirection

program 2> errorfile

stdin, stdout and stderr are represented by 0, 1 and 2 respectively. This allows one to select the stderr

stream:

find / 2> /dev/null

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process

FILE /

DEVICE

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STDERR Redirection

piped commands

program1 | program2

Pipes are represented by the “|” symbol. The data stream goes from the left to the right. The next figure

illustrates how the stdout for one process is redirected to the stdin for another process.

Piped Commands

cat /var/log/messages | less

NB Multiple output redirects are parsed from right to left, so the following commands are not equivalent.

Do-command 2>&1 >logfile

Do-command >logfile 2>&1

4. Metacharacters and Quotes

Metacharacters are characters that have special meaning for the shell. They are mainly used for file

globbing, that is to match several files or directory names using a minimum of letters.

The input (<), output (>) and pipe (|) characters are also special characters as well as the dollar ($) sign

used for variables. We will not list them here but note that these characters are seldom used to name

regular files.

Wildcards

● The * wildcard can replace any number of characters.

ls /usr/bin/b* lists all programs starting with a 'b'

● The ? wildcard replaces any one character.

ls /usr/bin/?b* lists all programs having a 'b' as the second letter

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FILE /

DEVICE

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Ranges

● [ ] is used to define a range of value.

ls a[0-9] lists all files starting with an 'a' and have a digit in second position. Also

ls [!Aa]* lists all files that don't start with an 'a' or an 'A'

● {string1,string2}; although not just a file naming wildcard, it can be used to match the names of existing

files.

ls index.{htm,html}

Quotes and escape codes

The special meaning of metacharacters can be cancelled by escape characters, which are also

metacharacters.

The backslash (\) is called the escape character and cancels the meaning of all metacharacters forcing

the shell to interpret them literally.

The single quotes (' ') cancel the meaning of all metacharacters except the backslash.

The double quotes (" ") are the weakest quotes but cancel most of the special meaning of the enclosed

characters except the pipe (|), the backslash (\) and a variable ($var).

The back tick

Back quotes `` will execute a command enclosed. The next example defines the variable TIME using the

date command.

TIME="Today's date is `date +%a:%d:%b`”

echo $TIME

Today's date is Sun:15:Jul

Another way of executing commands (similar to the back ticks) is to use $(). This will execute the

enclosed command and treat it as a variable.

TIME=$(date)

5. The Command History

To view the list of previously typed commands you can use the bash built-in command history.

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history

1 ls

2 grep 500 /etc/passwd

You can recall commands by using the Up-arrow and Down-arrow on your keyboard. There are also

emacs key bindings that enable you to execute and even edit these lines.

Emacs Key Bindings for Editing the Command History

Ctrl+P Previous line (same as Up-arrow)

Ctrl+n Next line (same as Down-arrow)

Ctrl+b Go back one character on the line (same as Left-Arrow)

Ctrl+f Go forward one character on the line (Same as Right-Arrow)

Ctrl+a Go to the beginning of the line (Same as <End>)

Ctrl+e Go to the end of the line (Same as <Home>)

The bang ! key can be used to rerun a command.

Example

!x executes the latest command in the history list starting with an 'x'

!2 runs command number 2 from the history output

!-2 runs the command before last

!! runs the last command

^string1^string2 run previous command and replace string1 by string2

6. Other Commands

Aliases

You can create aliases for commands needing many arguments. The format to create an alias is

alias myprog='command [options]{arguments}'

Command completion

By pressing TAB, the shell will complete the commands you have started typing in.

By typing alias alone at the command line you will get a list of currently defined aliases.

<< is a redirection for EOF

For example

cat << stop

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will accept standard input until the keyword 'stop' is entered.

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7. Exercise

Stdin-stdout-stderr

Type the next commands and represent the sequence of execution (if possible) using diagrams similar to

the ones used in this chapter.

ls /etc ; df > /tmp/out.1

(ls /etc ; df) > /tmp/out.2

find /etc -type f 2> /dev/null | sort

tr [a-z] [A-Z] < /etc/passwd | sort > /tmp/passwd.tmp

cat /tmp/passwd.tmp | tr [A-Z] [a-z]

Command Line

1. List all files in /usr/X11R6/bin that don't start with an x

ls /usr/X11R6/bin/[!x]*

2. The command xterm has the following options:

-bg <color> set background

-fg <color> set foreground

-e <command> execute ‘command’ in terminal

Set a new alias such that the su command opens a new color xterm and prompts for a root

password.

alias su=”xterm -bg orange -fg brown -e su - &”

Where would you store this alias on the system? ___________

3. You can encode files using uuencode. The encoded file is redirected to stdout.

For example: uuencode /bin/bash super-shell > uufile encodes /bin/bash and will produce a file called

super-shell when running uudecode against the uufile

- Mail the uuencoded /bin/bash to a local user (for this you can either use uuencode and a pipe | ,

or save the uuencoded output to a file uufile and use STDIN redirection <).

- Split the uuencoded file into 5 files:

uuencode /bin/bash super-shell > uufile

split –b 150000 uufile base-name.

This will create files called base-name.aa, base-name.ab, etc

To get a uuencoded file with all the original data (unsplit) do

cat base-name.* > uufile.new

Finally uudecode the file and check it still works.

uudecode uufile.new

This should create a binary file called super-shell

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3. Which tool finds the full path to a binary by scanning the PATH variable? _____

Variables

1. Do the following

Assign the value ‘virus’ to the variable ALERT.

ALERT=virus

Verify that it is defined using the set command:

set |grep ALERT

Is ALERT listed when using env instead of set?

Next type ‘bash’. Can you access the ALERT variable?

bash

echo $ALERT

NOTE the value of ALERT: ______ ( is it blank?)

Type exit (or ^D) to return to your original session.

Use the export command to make ALERT a global variable.

export ALERT

Verify that it is a global (env) variable

env | grep ALERT

(v)Start a new bash shell and make sure that ALERT is defined in the new shell:

bash

echo $ALERT

In this new shell, redefine the variable ALERT

export ALERT=green

Exit that shell. What is the value of ALERT in the original shell? ________

2. At the command prompt type the following lines:

CREDIT01=300;CREDIT02=400

for VAR in CREDIT01 CREDIT02;do echo $VAR;done

Notice that the variable VAR is referenced with $VAR.

(i) Rerun this command.

(ii) Rerun this command replacing CREDIT01 by $CREDIT01

3. Using appropriate quotes change your PS1 variable to include the full path to your working directory.

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(Hint: the value of PS1 is [\u@ \W]\$ , you only need to replace the \W by a \w)

PS1='[\u@\h \w ]\$ '

What does PS2 look like? ________

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File Management

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File Management

1. Moving around the filesystem

Absolute and relative paths

A directory or a file can be accessed by giving its full pathname, starting at the root (/) or its relative path,

starting from the current directory.

Absolute path: independent of the user's current directory

starts with /

Relative path: depends on where the user is

doesn't start with /

As in any structured filesystem there are a number of utilities that can help you navigate through the system.

The next two commands are built-in commands.

pwd: Gives your actual position as an absolute path.

cd: The 'change directory' command

2. Finding Files and Directories

We will describe the find, which, whereis and locate utilities.

find

Syntax:

find <DIRECTORY> <CRITERIA> [-exec <COMMAND> {} \;]

The DIRECTORY argument tells find where to start searching and CRITERIA can be the name of a file or

directory we are looking for.

Examples

find /usr/X11R6/bin -name ¨x*¨.

find / -user 502

Matching lines are listed to standard out. This output can be acted upon. For example delete the file, or

change the permission. The find tool has the build-in option –exec which allows you to do that. For example,

remove all files belonging to user 502:

find / -type f -user 502 –exec rm –f {} \;

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xargs

This tool is often thought of as a companion tool to find. In fact xargs will process each line of standard

output as an argument for another tool. We could use xargs to delete all files belonging to a user with:

find / -type f -user 502 | xargs rm –f

 Certain commands such as rm cannot deal with too long arguments. It is sometimes necessary to

delete all files in a directory with

ls |xargs rm -f

Common criteria switches for find

-type specify the type of file

-name name of the file

-user user owner

-atime, ctime, mtime access, creation and modified times (multiples of 24 hrs)

-amin, cmin, mmin access, creation and modified times (multiples of 1 min)

-newer FILE files newer than FILE

locate

Syntax:

locate <STRING>

When using locate all files and directories that match the expression are listed.

locate X11R

The search is much faster. In fact locate queries the /var/lib/slocate database. This database is kept up to

date via a daily cron job which runs updatedb.

When running updatedb from the command line the /etc/updatedb.conf file is read to determine pruned

files systems (e.g NFS) and directories (e.g /tmp)

which

Syntax:

which string

This tool will return the full path to the file called string by scanning the directories defined in the user's

PATH variable only. As a result which is only used to find commands.

whereis

Syntax

whereis string

This tool will return the full path to source or binaries as well as documentation files matching string by

scanning the PATH variable as well as a number of well known locations

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Getting the most from ls

Most common options for ls

-I show inode

-h print human readable sizes

-n list UIDs and GIDs

-p append descriptor (/=@) to list

-R recursively display content of directories

-S sort by file size

-t sort by modification time (similar to -c)

-u show last access time

3. Handling directories

Making a directory with mkdir:

When making a directory you can set the permission mode with the -m option. Another useful option is -p

which creates all subdirectories automatically as needed.

Example:

mkdir –p docs/programs/versions

Removing directories:

To remove a directory use either rmdir or rm -r. If you are root you may have to specify -f to force the

deletion of all files.

Notice: rm –rf /dir1/* removes all files and subdirectories leaving dir1 empty

rm –rf /dir1/ removes all files and subdirectories including dir1

4. Using cp and mv

Syntax:

cp [options] file1 file2

cp [options] files directory

It is important to notice that cp file1 file2 makes a new copy of file1 and leaves file1 unchanged.

Fig: file1 with inode 250 is copied to file2, duplicating the data to a new data area and creating a new inode

6238 for file2

I D

250

I D

6238

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You can also copy several files to a directory, using a list or wildcards. The following table lists the most used

options.

Most common options for cp

-d do not follow symbolic link (when used with -R)

-f force

-I interactive, prompt before overwrite

-p preserve file attributes

-R recursively copy directories

Note: cp –r /dir/* /dir2/ will copy all files and subdirectories omitting mydir

cp –r /mydir/ /dir2/ will copy all files and subdirectories including mydir

Syntax:

mv [options] oldname newname

mv [options] source destination

mv [options] source directory

The mv command can both move and rename files and directories. If oldname is a file and newname is a

directory then the file oldname is moved to that directory.

If the source and destination are on the same filesystem, then the file isn't copied but the inode information is

updated to specify the new location. Most common options are -f force overwrite and -i query interactively.

5. Hard Links and Symbolic Links

Symbolic links

A soft link to a file or a directory creates a new inode that points to the same data area:

ln -s lilo.conf lilo.sym

This is the listing for these files. Notice that the reference count is 1 for both files.

-rw------- 1 root root 223 Nov 9 09:06 lilo.conf

lrwxrwxrwx 1 root root 9 Nov 9 09:06 lilo.sym -> lilo.conf

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Fig2: A soft link to a file

I D

lilo.conf

lilo.sym

Soft links can be created across filesystems.

Hard Links

A hard link is an additional name for the same inode and as such the reference count of the file increases by

one for every new hard link.

ln lilo.conf lilo.link

In the listing notice that the reference count is 2 and that both files have the same size. In fact they are

identical.

-rw------- 2 root root 223 Nov 9 09:06 lilo.conf

-rw------- 2 root root 223 Nov 9 09:06 lilo.link

Hard links can only be created within the same filesystem.

7. Touching and dd-ing

touch

Another way of creating or modifying a file is to use touch.

Syntax: touch {options} file(s)

If file doesn't exist it is created. You can also change the access time of a file using the -a option, -m

changes the modification time and -r is used to apply the time attributes of another file.

Example:

touch file1.txt file2.txt creates new files

touch myfile -r /etc/lilo.conf myfile gets the time attributes of lilo.conf

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 To create a file called –errors use the – option:

touch -- -errors

This command copies a file with a changeable I/O block size. It can also be used to perform conversions

(similar to tr). Main options are if= (input file) of= (output file) conv= (conversion)

The conversion switch can be: lcase ucase ascii

Example:

dd if=/mnt/cdrom/images/boot.img of=/dev/fd0

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8. Exercises

File Navigation

Make a new directory in /tmp called /bin.

mkdir /tmp/bin

In /tmp/bin/ create a file called newfile (use touch, cat or vi).

Go to the root directory (cd /). View the content of newfile from there.

Which is the shortest command which will take you back to /tmp/bin ?

Which is the shortest command which will take you to your home directory ?

Is the PWD variable local or global ?

Creating and deleting directories

Which is the quickest way to make two new directories /dir1/dir2 ?

Remove the directories with rmdir then with rm.

Making space on the filesystem

In order to create more space on the device containing the directory /usr/share/doc we need to find a spare

device with enough space and copy the contents of /usr/share/doc to that device. Then we create create by

deleting the /usr/share/doc directory and creating a symbolic link point from /usr/share/doc to the new

location.

Make a directory called /spare on which we will mount suitable spare devices (one of the partitions created

in the previous exercises should be suitable.

mkdir /spare

mount <device> /spare

Test with df -h /spare and du -hs /usr/share/doc that the device is large enough to contain all of the existing

data.

Next, copy the contents of /usr/share/doc to /spare/

cp -a /usr/share/doc /spare

Make sure the data has all been copied across then edit /etc/fstab to make that device available at boot

time.

Delete /usr/share/doc and create a symbolic link pointing from /usr/share/doc to /spare/doc

ln -s /spare/doc /usr/share/doc

Do the same with /home. Any extra problems?

Finding Files on the System

Copy the file /etc/lilo.conf to /etc/lilo.conf.bak

1. Use find to find this new file

2. Use locate to find /etc/lilo.conf.bak. (How do you update the slocate database ?)

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Backup strategy (first step)

Find all files in your home directory that have been modified today.

find /home –mtime –1 |tee list1 |wc –-lines (-1 means less than one day)

We will introduce archiving tools later, but the output of the find command can be piped directly into cpio.

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Process Management

1. Viewing running processes

Processes have a unique Process ID the PID. This number can be used to modify a process' priority or to

stop it.

A process is any running executable. If process_2 has been spawned by process_1, it is called a child

process. The spawning process_1 is called the parent process.

The process family tree

The pstree command gives a good illustration of parent and child process hierarchy.

Figure 1: Part of the pstree output

bash(1046)---xinit(1085)-+-X(1086)

`-xfwm(1094)-+-xfce(1100)---xterm(1111)---bash(1113)-+-pstree(1180)

| |-soffice.bin(1139)---soffice.bin(1152)-+

-soffice.bin(1153)

| | |-soffice.bin(1154)

| | |-soffice.bin(1155)

| | |-soffice.bin(1156)

| | `-soffice.bin(1157)

| `-xclock(1138)

|-xfgnome(1109)

|-xfpager(1108)

|-xfsound(1107)

`-xscreensaver(1098)

In the above figure all the process' PIDs are shown; these are clearly incremental. The most common used

options are -p to display PIDs and -h to highlight a users processes only.

Finding running processes

A more direct way to determine which processes are running is to use ps. Most users have a set combination

of options which work for most situations. Here are three such options:

ps -ux all processes run by the user

ps T processes run under the current terminal by the user

ps aux all processes on the system

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It is recommended you read the ps manpage and choose your own best options!

ps accommodates UNIX-style and BSD-style arguments

usage: ps -[Unix98 options]

ps [BSD-style options]

ps --[GNU-style long options]

ps –help for a command summary

Summary of options

-a show all processes for the current user linked to a tty (except the session leader)

-e or -A show all processes

-f gives the PPID (Parent Process ID) and the STIME (Start Time)

-l is similar to -f and displays a long list

a show all processes linked to a tty, including other users

x show all processes without a controlling tty as well

Continuously updating process information

The top utility will update information on processes at an adjustable rate.

While top is running you can type h for a list of commands. The space bar will update information instantly.

You can also use top to change a process' priority as we shall see in the next section.

2. Modifying Processes

Stopping processes

The kill command can be used to send signals to processes. There are 63 signals available. The default

signal terminates a process and is called SIGTERM with value 15.

kill

Syntax

kill SIGNAL process_PID

Every process can choose whether or not to catch a signal except for the SIGKILL which is dealt with by the

kernel. Most daemons redifine the SIGHUP to mean “re-read configuration file”.

Most Common Signals

1 or SIGHUP hangup or disconnect the process

2 or SIGINT same as Ctrl+C interrupt

3 or SIGQUIT quit

9 or SIGKILL kill the process through a kernel call

15 or SIGTERM terminate a process 'nicely'. This is the DEFAULT signal.

One can also stop processes without knowing the process' PID using killall.

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killall

Syntax

killall SIGNAL process_NAME

Fig1: Interprocess signaling

Process priority and nice numbers

Nice numbers (NI) alter the CPU priority and are used to balance the CPU load in a multiuser environment.

Each process is started with a default nice number of 0. Nice numbers range from 19 [lowest] to -20 [highest].

Only root can decrease the nice number of a process. Since all processes start with a default nice number of

zero as a consequence negative nice numbers can only be set by root!

nice numbers and CPU priorities

19 NI PRI

users

0 (default)

root

-20 Pool of processes 0

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To modify a process' priority that is already running use renice. To set a process' priority use nice.

Syntax

Nice –<NI> <process>

renice <+/-NI> -p <PID>

Notice that renice works with PIDs and handles lists of processes at a time. A useful option to renice is the

-u option which affects all processes run by a user.

Set nice number 1 for processes 234 and 765:

renice +1 -p 234 765

Set nice number -5 for xclock:

nice --5 xclock

3. Processes and the shell

background and forground processes

After you have started a process from the shell you automatically leave the shell interpreter. You will notice

that no commands will respond. The reason for this is that it is possible to run programs in the foreground fg

or in the background bg of a shell.

When a program is running in the foreground it is possible to recover the shell prompt but only by interrupting

the program for while. The interruption signal is Ctrl Z.

Stopping and starting jobs

A process started from a shell is also called a job. Once the job receives the ^Z signal it is stopped and the

shell prompt is recovered. To restart the program in the background simple type: bg.

Example

[mike localhost /bin]$xclock

xclock running in forground, shell prompt lost

[1]+ Stopped xclock xclock received ^Z signal

[mike localhost /bin]$bg shell prompt recovered, issue the bg command

[1]+ xclock & xclock is running in the background

[mike localhost /bin]$

Notice the [1]+ symbol above. The integer is the process' job number, which it can be referred to as.

The '+' sign indicates the last modified process. A '-' sign would indicate the second last modified process.

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Listing jobs

The jobs utility lists all running processes started from the current shell. The job number, the job's state

(running/stopped), as well as the two last modified processes, will be listed.

Output for jobs

[1]- Stopped xclock

[2] Running xman &

[3]+ Stopped xload

The job number

One can conveniently stop and start a selection of jobs using the job number. This is achieved with the fg

command.

Calling job 2 to the foreground and killing job 1

fg 2 or

fg %2 or

fg %?xma

kill –9 %1

Avoiding HUP with nohup

Finally there is a program called nohup which acts as a parent process independently from the user’s

session. When a user logs off, the system sends a HUP to all processes owned by that process group. For

example, to avoid this HUP signal a script called bigbang which attempts to calculate the age of the Universe

should be started like this:

nohup bigbang &

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4. Exercises

You should run X before starting these exercises.

1. Check the current nice value of your running x-terminal. Change this value using top or renice.

2. What is the equivalent signal of a ^Z sent to a process? (List all signals with kill –l)

3. Which signal is redefined for most daemons and forces the configuration file to be reread?

4. What is the default signal sent to a process, using kill or killall?

5. Which signal is directly handled by the kernel and cannot be redefined?

6. Make sure you log into a virtual terminal (tty1 to tty6) before doing this. We want to run a script that will

continue to run once we logout using the nohup parent process.

In the /tmp directory create a file called print-out with the following content:

#!/bin/bash

count=0

while (true) do

echo this is iteration number $count

let count+=1

done

We first do the following (without using nohup) :

cd /tmp

./print-out &

exit

You may not see the command line when typing exit but this should log you out. When you log back

in check that print-out is no longer running

ps ux | grep print-out

Next start the command with

nohup /tmp/print-out &

exit

Log back in and test these commands

ps ux |grep print-out

tail -f ~/nohup.out

Ctrl+C

killall print-out

ps ux|grep print-out

tail -f ~/nohup.out

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Text Processing

1. cat the Swiss Army Knife

cat the editor

The cat utility can be used as a rudimentary text editor.

cat > short-message

we are curious

to meet

penguins in Prague

Crtl+D

Notice the use of Ctrl+D. This command is used for ending interactive input.

cat the reader

More commonly cat is used only to flush text to stdout. Most common options are

-n number each line of output

-b number only non-blank output lines

-A show carriage return

Example

cat /etc/resolve.conf

► search mydomain.org

nameserver 127.0.0.1

tac reads back-to-front

This command is the same as cat except that the text is read from the last line to the first.

tac short-message

► penguins in Prague

to meet

we are curious

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2. Simple tools

using head or tail

The utilities head and tail are often used to analyse logfiles. By default they output 10 lines of text. Here are

the main usages.

List 20 first lines of /var/log/messages:

head -n 20 /var/log/messages

head -20 /var/log/messages

List 20 last lines of /etc/aliases:

tail -20 /etc/aliases

The tail utility has an added option that allows one to list the end of a text starting at a given line.

List text starting at line 25 in /var/log/messages:

tail +25 /etc/log/messages

Exercise: If a text has 90 lines, how would you use tail and head to list lines 50 to 65? Is there only one way

to do this ?

Finally tail can continuously read a file using the -f option. This is most useful when you are expecting a file to

be modified in real time.

counting lines, words and bytes

The wc utility counts the number of bytes, words, and lines in files. Several options allow you to control wc's

output.

Options for wc

-l

count number of lines

-w

count number of characters or words

-c or -m

count number of bytes or characters

Remarks:

With no argument wc will count what is typed in stdin.

numbering lines

The nl utility has the same output as cat -b.

Number all lines including blanks

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nl -ba /etc/lilo.conf

Number only lines with text

nl -bt /etc/lilo.conf

replacing tabs with spaces

The expand command is used to replace TABs with spaces. One can also use unexpand for the reverse

operations.

viewing binary files

There are a number of tools available for this. The most common ones are od (octal dump) and hexdump.

3. Manipulating text

The following tools modify text layouts.

choosing fields and characters with cut

The cut utilility can extract a range of characters or fields from each line of a text.

The –c option is used to manipulate characters.

Syntax:

cut –c {range1,range2}

Example

cut –c5-10,15- /etc/password

The example above outputs characters 5 to 10 and 15 to end of line for each line in /etc/password.

One can specify the field delimiter (a space, a commas etc ...) of a file as well as the fields to output. These

options are set with the –d and –f flags respectively.

Syntax:

cut -d {delimiter} -f {fields}

Example

cut -d: -f 1,7 --output-delimiter=" " /etc/passwd

This outputs fields 1

and 7

of /etc/passwd delimited with a space. The default output-delimiter is the same

as the original input delimiter. The --output-delimiter option allows you to change this.

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joining and pasting text

The easiest utility is paste, which concatenates two files next to each other.

Syntax:

paste text1 text2

With join you can further specify which fields you are considering.

Syntax:

join -j1 {field_num} -j2{field_num} text1 text2 or

join -1 {field_num} -2{field_num} text1 text2

Text is sent to stdout only if the specified fields match. Comparison is done one line at a time and as soon as

no match is made the process is stopped even if more matches exist at the end of the file.

sorting output

By default, sort will arrange a text in alphabetical order. To perform a numerical sort use the -n option.

formatting output

You can modify the number of characters per line of output using fmt. By default fmt will concatenate lines

and output 75 character lines.

fmt options

-w number of characters per line

-s split long lines but do not refill

-u place one space between each word and two spaces at the end of a sentence

translating characters

The tr utility translates one set of characters into another.

Example changing uppercase letters into lowercase

tr '[A-B]' '[a-b]' < file.txt

Replacing delimiters in /etc/passwd:

tr ':' ' ' < /etc/passwd

Notice: tr has only two arguments! The file is not an argument.

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4. Exercises

1. Use cat to enter text into a file called message.

cat >> message

line 1

Do the same but use the keyword STOP instead of the predefined eof control (^D).

cat >> message << STOP

line 2

STOP

Next, append text to message using echo.

echo line 3 >> message

2. Create a file called index with two fields REFERENCE and TITLE separated by a space.

e.g 001 Using_Linux

Create a second file pricing with two fields REFERENCE and PRICE separated by a space

e.g 001 9.99

Use join to display the reference, title and prices fields.

3. Using tr replace all colons by semi-colons in /etc/passwd.

Do the same using cut.

4. Use head and tail to list lines 70 to 85 of /var/log/messages.

5. Use the cut utility together with grep and ifconfig to printout only the IP address of the first

network interface eth0.

6. In /tmp make a directory called files

mkdir /tmp/files

Create 50 files in that directory:

#!/bin/bash

count=0

while [ $count -lt 50 ] do

touch /tmp/files/$count.txt

let count+=1

done

We want to change all the txt extensions to dat extentions. For this we need to type the following on the

command line:

for FILES in $(ls *.txt)

FILENAME=$(echo $FILES| cut -d. -f1)

mv $FILES $FILENAME.dat

done

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Software Installation

1. Introduction

We begin with a short code example. Although we don’t need an advanced understanding of the C language,

these examples can help trouble shoot common situations.

The main.c file:

#include<stdlib.h>

int main(){

Hello();

}

The Hello.c file:

#include<stdio.h>

void Hello(){

printf(“Hi ! \n”);

}

Notice that the main.c is incomplete in the sense that the Hello() function is undefined. In the same way

Hello.c doesn’t have a “main” declaration. So these files are interdependent. One can however compile

object files (.o) which are like non-executable binary files which can be used to ‘build’ an application.

Compiling the object files:

gcc –c main.c

gcc –c Hello.c

This will generate two files main.o and Hello.o which can now be used to build the application app.

Compiling app :

gcc –o app main.o Hello.o

The –o option simply specifies a name for the compiled code. If no name is specified the compiled output is

called a.out by default.

All these steps can be automated using a Makefile. Here is a minimal Makefile which would compile the app

executable.

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Makefile

SHELL = /bin/sh

CC = /usr/bin/gcc

app: main.o Hello.o

$(CC) –o app main.o Hello.o

main.o: main.c

$(CC) –c main.c

Hello.o: Hello.c

$(CC) –c Hello.c

2. Static and Shared Libraries

Often used functions are archived as libraries. During compilation these libraries can be linked to the code

which uses the library function calls. The library can either be statically or dynamically linked to the code.

The gcc compiler can link libraries in a variety a ways (many options). However by default it will link files that

are given on the commandline that don’t have a .c extention (only the .c files are treated as code).

Listing 1: Linking by default

gcc main.c Hello.o

This will produce an a.out executable with the Hello.o object statically linked to it.

● Static libraries

Static libraries are archived .o files. These archives are created with the ar tool and have a .a extention.

Listing2: adding an object file to an archive:

ar rcs libfoo.a file1.o file2.o

● Dynamic/Shared Libraries

A shared library is a library that will be loaded by the program when it is executed. One also says that the

library is dynamically loaded.

Listing 3: Creating a shared library:

gcc –c –fPIC Hello.c creates the object file

gcc –shared –W1,soname,libfoo.so.1 –o libfoo.so.1.0 Hello.o

The –fPIC flag enables the Position Independent Code generation.

Listing4: Compiling with a shared library:

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gcc main.c libfoo.so.1.0

This will produce an a.out executable. However if you try to run this it will complain with the error message

listed below.

Shared library not found error:

./a.out: error while loading shared libraries: libfoo.so.1.0: cannot open

shared object file: No such file or directory

In the next section we will see what can be done to fix this problem.

● Shared Library naming and dynamic loading

We will use the above example to understand how Linux libraries are maintained.

Figure 1: The Shared Library Names

To find out which shared libraries an executable needs at execution time the ldd tool is used.

Example:

ldd a.out

► libfoo.so.1.0 => not found

libc.so.6 => /lib/libc.so.6 (0x40028000)

/lib/ld-linux.so.2 => /lib/ld-linux.so.2 (0x40000000)

Notice that libfoo.so.1.0 is not found. This is because the a.out needs to dynamically load this library

and the dynamic linker ld.so is not aware of this new library.

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To fix this problem one can do one of the following:

1. If the binary needs to be temporary tested define the LD_LIBRARY_PATH variable as follows:

export LD_LIBRARY_PATH=$(pwd)

2. copy the libfoo.so.1.0 to /usr/lib/ and run ldconfig to update the ld cache.

The GNU specification advises libraries to be stored in /usr/local/lib. These guidelines are

followed by developers and most tarballed code will install libraries in that directory and the binaries

in /usr/local/bin. Installing and removing this code from the system would be done by ¨make

install¨ and ¨make uninstall¨.

The FHS (Filesystem Hierarchy Standard) recommends libraries be kept in /usr/lib/ and

associated binaries in /usr/bin/. This convention standard is adhered to by Linux distributions.

In effect mature and stable code is stored in /usr/ rather than /usr/local/ and the two

standards do not lead to any contradictions. Installing and removing this code code would be done

using the rpm command.

NOTICE

With certain distributions the /usr/local/lib/ directory is not scanned by ldconfig. It is simply a

matter of adding this directory to /etc/ld.so.conf and ... reboot?

3. Source Distribution Installation

Open source projects are often distributed as tarballs (i.e compressed tarred archives). Many development

environments (glade, kdevelop…) generate the files that help facilitate compiling and installation of a project.

Common Files

configure: This is a script which determines what architecture is being used. It also checks that the required

compiler and libraries are present. The safest way to run the script is to use ‘./configure’.

Makefile: This acts like a configuration file for the make utility. The main information provided is:

- The name of the compiler and compiling options

- The path to the shared libraries and header files

- Mapping between code files (.c) and object files (.o)

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Compilation

If the files above are present then there is a good chance that you will successfully ‘port’ the program to your

computer. Here are the routine steps:

./configure

make

make install

make install must be run as root if the install directory is /usr/ or /usr/local

There are many options to the ./configure script. To customise your installation you could type ./configure –

help.

An easy option is --prefix which allows you to specify the root directory for the installation. This is usually

set to /usr/local/ by default.

4. The RedHat Package Manager RPM

Fig 1: Package Manager Functions

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Package naming

Rpm packages generally follow the following naming convention:

name-version-release.architecture.rpm

Major modes

These are the major modes for rpm.

Short Long Description

-i

–install Installs the package

-U

–update Updates or installs a package

-F

--freshen Updates only installed package

-V

--verify file size, MD5, permissions, type ...

-q

--query Queries installed/uninstalled packages, and files

-e

–erase Uninstall package

Minior mode

Short Description

applies to all installed packages

c together with q lists configuration files

d together with q lists docomentation files

adds hashes while processing

i together with q lists information about a package

l together with q lists all files and directories in a package

p together with q specifies that the query is performed on the package file

verbose

Query modes

We consider for example the package routed-0.17.i386.rpm. We can query this package and list its contents

before installation with the l option as follows:

rpm –qpl routed-0.17.i386.rpm

Once this package is install we can query the installed package as with:

rpm –ql routed-0.17 or

rpm –ql routed

Finally if we want to find out which package installed the file /usr/sbin/routed the rpm database can be

queried with:

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rpm –qf /usr/sbin/routed

Three query types: uninstalled packages, installed packages and files

Query Type Option

Package file

-qp

Installed package

-q

File

-qf

An extra option will allow you to get information on all installed files –l, documentation –d configuration files –

c, etc ...

Special options

--nodeps this allows to install without regard to dependencies

--force force an upgrade

--test doesn’t actually install or upgrade, just prints to stdout

--requires show package requirement

Going Further: Building RPM packages (not for LPI exam purpous)

NOTICE:

This is additional information, this paragraph is not an LPI 101 objective. When doing this section you may

encounter problems with the –rebuild option, this is due to the fact that the new versions of RPM use

rpmbuild instead of rpm when rebuilding packages.

The source code for many RPM packages is also available as an RPM package and will be used to build a

binary package. The naming convention is:

name-version-release.src.rpm

These packages contain at least two files, the tarball with the code and a spec file. The spec file contains

instructions to patch, compile and build the RPM package. If the code needs to be patched before

compilation then the patches are included in the source package.

There are three different ways to build a RPM package. We will assume that we have a package called

name-version-release.src.rpm.

 For these methods to work you first need to install the rpm-build package

Method 1:

Install the RPM source package with:

rpm –ivh name-version-release.src.rpm

This will copy files to the following directories:

/usr/src/redhat/SPECS

/usr/src/redhat/SOURCES

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In the /usr/src/redhat/SPECS directory there is now a file called name.spec (where ‘name’ is the name

of the package). To start building the compiled package, that is name-version-release.i386.rpm, we type in

the following command:

rpm –ba name.spec

This will start a series of scripts. The tarball in /usr/src/redhat/SOURCES will be unpacked in /

usr/src/redhat/BUILD.

If the compilation succeeds then the built binary package will be saved in /usr/src/redhat/RPMS/.

There are different subdirectories corresponding to various CPU models/generations. If the compilation didn’t

involve specific features from these chips then the package will be saved in the noarch directory.

Method 2:

This method triggers the same chain of events as the previous one but is started with the following single

command:

rpm –-rebuild name-version-release.src.rpm

Method 3:

In some cases developers will distribute a tarball together with a spec file. If the tarball is called name-

version-release.tar.gz you can search for a .spec file with the following:

tar tzvf name-version-release.tar.gz | grep .spec

If the tarball has a spec file then you can build an RPM package by typing:

rpm –bt name-version-release.tar.gz

5. The Alien Tool

This tool will change Debian packages into RedHat ones and vice versa. You can download it at:

http://kitenet.net/programs/

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6. Exercises

In the following examples download a source RPM file (e.g. bash-2.05-8.src.rpm for RedHat 7.2) from

www.rpmfind.net.

1. Installing as a tarball.

- Extract the contents of the RPM package without compiling anything with:

rpm –ivh bash-2.05-8.src.rpm

- In the /usr/src/redhat/SOURCES directory, unpack the tarball with:

tar xvzf bash-2.05-8.tar.gz

- Optional (recommended!): The patches can be applied. Depending on which directory you are in

the syntax will vary.

From /usr/src/redhat/SOURCES:

patch –p0 –b < file.patch

From /usr/src/redhat/SOURCES/bash-2.05-8

patch –p1 –b < file.patch

- Finally follow the usual compilation steps:

./configure

make

If you are sure you want to install this package then make install but remember that this will not install the

software using the package manager.

2. Rebuilding with the RPM package manager.

rpm –rebuild package.src.rpm

The compiled binary package should be in /usr/src/redhat/RPMS

- Check the package’s contents with the –qpl option

- Install the package(s), and run queries on the installed package

- Uninstall the package

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Advanced Text Manipulation

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Advanced Text Manipulation

Finding a word or multiple words in a text is achieved using grep, fgrep or egrep. The keywords used

during a search are a combination of letters called regular expressions. Regular expressions are

recognised by many other applications such as sed, and vi.

1. Regular Expressions

Table1:List of main regex’s

Characters Search Match

x (or any character)

Strings containing an ‘x’

\<KEY

Words beginning with ‘KEY’

WORD\>

Words ending with ‘WORD’

Beginning of a line

End of a line

[ Range ]

Range of ASCII characters enclosed

[^c ]

Not the character ‘c’

Interpret character ‘[‘ literally

“cat*”

Strings containing ‘ca’ or ‘cat’ plus anything

“.” Match any single character

Extended regex: The main eregex’s are: +,?,() and |

Table2: List of main eregex

Characters Search Match

“A1|A2|A3”

Strings containing ‘A1’ or ‘A2’ or ‘A3’

“cat+”

Strings containing at least cat plus anything

“cat?”

Strings containing ‘ca’ or ‘cat’ plus anything

2. The grep family

basic grep

The grep utility supports regular expressions regex such as those listed in table1.

egrep

The egrep tool supports extended regular expressions eregex such as those listed in table2.

fgrep

Fgrep stands for fast grep and fgrep interprets strings literaly (no regex or eregex support)

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3. Working with grep

Syntax for grep:

grep PATTERN FILE

grep

Main Options

-c

count the number of lines matching PATTERN

-f

obtain PATTERN from a file

-i

ignore case sensitivity

-n

indicate the input file's line number

-v

output all line except those containing PATTERN

-w

match exact PATTERN

For example list all non blank lines in /etc/lilo.conf:

grep –v “^$” /etc/lilo.conf

4. egrep and fgrep

The fgrep utility does not recognise the special meaning of the regular expressions. For example

fgrep ‘cat*’ FILE

will only match words containing ‘cat*’. The main improvement came from fgrep’s ability to search from a

list of keywords entered line by line in a file, say LIST. The syntax would be

fgrep –f LIST FILE

The egrep utility will handle any modern regular expressions. It can also search for several keywords if

they are entered at the commandline, separated by pipes. For example;

egrep “linux|^image” /etc/lilo.conf

5. The Stream Editor - sed

At this point the stream editor makes its appearance! It is an old type of tool and originally the only one

available under UNIX to manipulate text.

The sed utility is most often used to search and replace patterns in text. It supports most regular

expressions.

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5.1 Beginning sed

Syntax for sed

sed [options] ´command’ [INPUTFILE]

The input file is optional since sed also works on file redirections and pipes.

Here are a few examples assuming we are working on a file called MODIF.

Delete all commented lines:

sed ‘/^#/ d ’ MODIF

Notice that the search pattern is between the double slashs //.

Substitute /dev/hda1 by /dev/sdb3:

sed ‘s/\/dev\/hda1/\/dev\/sdb3/g’ MODIF

The s in the command stands for ‘substitute’. The g stands for “globally” and forces the substitution to

take place throughout each line.

If the line contains the keyword KEY then substitute ‘:’ with ‘;’ globally:

sed ‘ /KEY/ s/:/;/g’ MODIF

5.2 More Advanced sed

You can issue several commands each starting with –e at the command line. For example, (1) delete all

blanks then (2) substitute ‘OLD’ by ‘NEW’ in the file MODIF

sed –e ‘/^$/ d’ -e ‘s/OLD/NEW/g’ MODIF

These commands can also be written to a file, say COMMANDS. Then each line is interpreted as a new

command to execute (no quotes are needed).

An example COMMANDS file

1 s/old/new/

/keyword/ s/old/new/g

23,25 d

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The syntax to use this COMMANDS file is:

sed -f COMMANDS MODIF

This is much more compact than a very long commandline !

Summary of options for sed

Commandline flags

-e Execute the following command

-f Read commands from a file

-n Do not printout unedited lines

Command options

d Delete an entire line

r Read a file and append to output

s Substitute

w Write output to a file

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6. Exercises

1. Create a new file called FILE containing the lines:

Using grep,

fgrep and

egrep

to grep for 99% of the cats

% these are two

% commented lines

- Use grep to output only uncommented lines.

- Find all lines containing ‘grep’ exactly. (Not ‘egrep’ nor ‘fgrep’.Use -w to match the word)

- Find lines containing words starting with an ‘a’

2. Regular expressions. Append the following lines to the previous file:

cat

cats

catss

cat+

cat*

cat?

car

carriage

- Investigate the outcome of the following using grep, egrep and fgrep:

grep ‘cat+’ FILE

grep ‘cat?’ FILE

grep ‘cat.’ FILE

grep ‘cat*’ FILE

3. Use sed to do the following changes in FILE

(use a COMMAND file, then do everything on the commandline)

- in the first line substitute ‘grep,’ with ‘soap’

- delete ‘fgrep’ in the second line

- substitute ‘egrep’ with ‘ water’

- in the fourth line replace ‘grep for’ with 'wash'

Save the result to a file using the w option

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Using vi

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Using vi

In most Linux distributions vi is the text editor of choice. It is considered an essential admin tool such as

grep or cat and is found therefore in the /bin directory.

1. vi Modes

In order to perform complex operations such as copy/paste vi can operate in different modes.

● Command mode

This is the editing and navigation mode. Commands are often just a letter. For example use j to jump to

the next line.

As a rule of thumb if you want to perform an operation several times you can precede the command by a

number. For example 10j will jump 10 lines.

● Last Line (or column) Mode

You enter this mode from the command mode by typing a colon. The column will appear at the bottom

left corner of the screen. In this mode you can perform a simple search operation, save, quit or run a

shell command.

● Insert Mode

The easiest way to enter this mode while in command mode is to use i or a. This mode is the most

intuitive and is mainly used to interactively enter text into a document.

 The Esc key will exit the insert mode and return to command mode

2. Text Items

Items such as words and paragraphs are defined in command mode to allow editing commands to be

applied to text documents without using a mouse.

Word, sentences and paragraphs

e resp. b Move to the end/begining of the current word

( resp. )

Move to the begining/end of the current sentence

{ resp. }

Move to the begining/end of the current paragraph

w Similar to e but includes the space after the word

Beginning and End

Beginning of line

End of line

Beginning of file

End of file

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All these text items can be used to navigate through the text one word (w) or paragraph (})at a time, go

to the beginning of a line (^) the end of the file (G) etc. One can also use these text items to execute

commands such as deleting and copying.

3. Inserting Text

When in command mode typing i will allow you to enter text in the document interactively. As with all

other features in vi there are many other ways of doing this. The table below lists all possible inserting

modes.

Insert commands

a Append text with cursor on the last letter of the line

A Append text with cursor after last letter at the end of the line

i Insert text at the current position

o Insert text on a new line below

O Insert text on a new line above

s Delete the current letter and insert

S Delete current line and insert

4. Deleting Text

If you want to delete a single character while in command mode you would use x and dd would delete

the current line.

Remark: Nearly all vi commands can be repeated by specifying a number in front of the command. You

can also apply the command to a text item (such as word., sentence, paragraph ...) by placing the entity

after the command.

Table4:Words and Characters

single word

single character

Examples:

Delete a word:

Delete text from here to the end of the current line

Delete text from here to the end of the current paragraph

One can simultaneously delete an item and switch to insert mode with the c command. As usual you can

use this command together with a text item such as w or {.

5. Copy Pasting

The copy action in vi is the command y (for yank), and the paste action is p.

If an entire line is yanked the pasted text will be inserted on the next line below the cursor.

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The text selection is made with the familiar text items w, l, }, $ etc ... There are a few exceptions such as

the last example.

Examples:

Copy the text from here to the end of the current line

Copy the entire current line

Copy 3 lines

3yy

 The latest deleted item is always buffered and can be pasted with the p command. This is equivalent

to a cut-and-paste operation

6. Searching

Since searching involves pattern matching we find ourselves once again dealing with regular expressions

(regex). As many UNIX text manipulation tools such as grep or sed, vi recognises regular expressions

too.

To perform a search one must be in colon mode. The / (forward slash) command searches forward and

the ? command searches backwards.

One can also perform search and replace operations. The syntax is similar to sed.

Example:

Search for words beginning with ‘comp’ in all the text

/\<comp

Search for lines starting with the letter z

/^z

Search in the whole text for the keyword ‘VAR’ and replace it by ‘var’

:% s/VAR/var

7. Undoing

At this stage is is worth mentioning that one can always undo changes (while in command mode) with the

u command, and this as long as one hasn’t saved the file yet.

8. Saving

The command for saving is w. By default the complete document is saved. One can also specify an

alternative name for the file. Portions of the text can be saved to another file while other files can be read

and pasted in the current document. Here are the examples which illustrate this.

Examples:

Save the current document as ‘newfile’

:w newfile

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Save lines 15 to 24 in a file called ‘extract’

:w 15,24 extract

Read from file ‘extract’. The text will be pasted at the cursor

:r extract

Warning: In the column mode context we have the following

. is the current line

$ is the end of the document

9. Exercises

As root cp /var/log/messages to /tmp. Using vi’s search and replace utility make each line begin with

print “ and end with “;

Type “u” to undo all the changes

Copy /etc/lilo.conf to /tmp, edit this file and try to copy/paste yy/p and cut/paste with dd/p

Investigate the outcome of :x, ZZ, :quit, :wq, and :q! (which ones save and which one don't?)

Investigate the outcome for the various inserting modes: A, a, O, o, S and s

Optional: If you have time the vim-enhanced package installs a program called vimtutor which takes

you through most common vi options.

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The X Environment

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The X Environment

1. Introduction

The X Windows system was developed as the display component of Project Athena at the

Massachusetts Institute of Technology. It is the graphical environment for UNIX. The X Window system

for Linux is based on the freely distributable port of X Window version 11 release 6 (Commonly referred

to as X11R6).

This freely distributable port is commonly known as xfree86 for the 80386/80486 and Pentium processor

families. Since its initial port, Xfree86 has been ported to other computing platforms, including System

V/386 and 386BSD.

X11R6 Components and Configuration Sections

Section Files Section Monitor

Section InputDevice Section InputDevice Section Device

Section Pointer (old) Section "Keyboard" (old)

The above diagram shows the components of the X11R6 server. The “Section” names refer to

configuration sections in the XF86Config configuration file (covered in the next section).

The two clients depicted on top of the server are so-called x-applications (e.g xclock or xterm). The

window manager is also a client. Window managers add “windowing” facilities around the other x-

application clients, allowing functionalities such as window dragging, focus, iconification, etc.

NOTICE:

The X11R6 server is independent from the clients that run on top. Clients are configured using specific

configuration files or global files usually called Xdefaults or Xresources. The X server configuration

file will only configure components such as the font server and font directories, mouse, keyboard,

monitor resolution and color depth.

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mouse

xfs

video

keyboard

monitor

client A

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The X Environment

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2. Configuring X11R6

Two of the configuration utilities provided with the Xfree86 software are the XF86Setup and xf86config

scripts. Other vendors have specific utilities such as:

Xconfigurator, redhat-config-xfree86 (RedHat)

XFdrake (Mandrake)

sax (Suse)

● The XF86Config File

All the above mentioned configuration utilities will create and edit the XF86Config configuration file. This

file is read at start up by the X Server and determines its behaviour. This file is typically found in the /

etc/X11 directory, and this is its’ full path: /etc/X11/XF86Config.

There are 11 configuration sections in the config file, they are listed below:

ServerFlags

Module

InputDevice

Device

VideoAdapter

Monitor

Modes

Screen

ServerLayout

DRI

Vendor

NOTICE:

The obsolete section names Keyboard and Pointer are still recognised for compatability reasons, the

new section name is now InputDevice

One of the first sections is the Section “Files”. The FontPath keyword tells whether to get fonts from a

local directory or from a font server. The RgbPath keyword is used to indicate the full path to rgb text file

used to map color names to RGB notation:

Section “Files”

FontPath “/path/to/fonts/dir/”

FontPath “trans/hostname:port”

RgbPath "/path/to/rgb"

EndSection

Where trans is the transport type unix, hostname is the fully qualified domain name of the font server,

and port is the port to connect to, usually port 7100.

Example:

FontPath “unix/:7100” # Local Font Server

FontPath “unix/myfontserver.mydomain.com:7100”

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Below is a sample XF86Config file :

Section "Files"

RgbPath "/usr/X11R6/lib/X11/rgb"

FontPath

"/usr/X11R6/lib/X11/fonts/misc:unscaled,/usr/X11R6/lib/X11/fonts/75dpi:unsc

aled,/usr/X11R6/lib/X11/fonts/100dpi:unscaled,/usr/X11R6/lib/X11/fonts/misc

EndSection

Section "InputDevice"

Identifier "Keyboard0"

Driver "keyboard"

EndSection

Section "InputDevice"

Identifier "Mouse0"

Driver "mouse"

Option "Protocol" "IMPS/2"

Option "Device" "/dev/psaux"

Option "ZAxisMapping" "4 5"

EndSection

Section "Monitor"

Identifier "Primary Monitor"

VendorName "Unknown"

ModelName "Unknown"

HorizSync 31.5-37.9

VertRefresh 55-90

Modeline "800x600" 40.00 800 840 968 1056 600 601 605 628 +hsync

+vsync

EndSection

Section "Device"

Identifier "Primary Card"

VendorName "Unknown"

BoardName "None"

VideoRam 2048

EndSection

Section "Screen"

Driver "Accel"

Device "Primary Card"

Monitor "Primary Monitor"

DefaultColorDepth 24

BlankTime 0

SuspendTime 0

OffTime 0

SubSection "Display"

Depth 24

Modes "800x600"

EndSubSection

SubSection "Display"

Depth 32

Modes "800x600"

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3. Controlling X clients

X clients are configured using the .Xresources or .Xdefaults file. These file are kept in the users home directory. It

is not automatically created by default, as system-wide defaults are also available for each program.

Below is an extract from a .Xresources:

xterm_color*background: Black

xterm_color*foreground: Wheat

xterm_color*cursorColor: Orchid

xterm_color*reverseVideo: false

xterm_color*scrollBar: true

xterm_color*saveLines: 5000

xterm_color*reverseWrap: true

xterm_color*font: fixed

xterm_color.geometry: 80x25+20+20

xterm_color*fullCursor: true

xterm_color*scrollTtyOutput: off

xterm_color*scrollKey: on

term_color*VT100.Translations: #override\n\

<KeyPress>Prior : scroll-back(1,page)\n\

<KeyPress>Next : scroll-forw(1,page)

xterm_color*titleBar: false

Each of these directives is a system default directive that describes how a client will be displayed. Each

line consists of the client name followed by an asterisk and the X Window parameter. Through a carefully

configured .Xresources file the user can define the way a client will look each time it is started.

4. Starting X

An X session can be started using 2 methods:

Method 1: From the command line, after logging in onto a virtual terminal the user launches the X Server

using a script called startx

Method 2: A Display Manager is running prompting the user with a graphical login, in runlevel 5.

1. From the Command Line

The startx script starts xinit. The xinit script has two main arguments (a) the X server and (b) the

xinitrc script. The xinitrc script will source (read) the files Xresourses (controlling the x-applications)

and the Xclients (choosing a window manager). So we can symbolise the startup sequence as follows:

startx --> xinit --> X -> xinitrc -> Xclient (wm/desktop)

2. Using a Display Manager

We will first describe the login. The next section covers all the functionalities of the Display Manager.

xdm --> xlogin --> Xsession --> Xclient

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5. The Display Manager

There are three main display managers, xdm (generic), gdm (GNOME) and kdm (KDE). According to the

LPI objectives the configuration file are in the following directories:

/etc/X11/xdm/

/etc/X11/gdm/

/etc/X11/kdm/

However kdm no longer follows this convention. So we will take a closer look at xdm and gdm.

Display Managers are used mainly in run level 5 to allow local users to log onto the system using the

graphical interface. However display managers can also be used to provide a graphical login interface

over the network. To do this they use a protocol called XDMCP or X Display Manager Control Protocol.

By default XDMCP is disabled (we will enable XDMCP as an exercise).

X server and Display Manager

Welcome !!

Display Manager

(x-application)

xlogin

password

X11R6

● Configuration Files

/etc/X11/xdm/Xrescources

Since the Display Manager is also an x-application, the fonts, the background colors and xlogin

can be configured with the Xresourses file in /etc/X11/xdm/. When using gdm, the

/etc/X11/gdm/Init/Default script will source Xresources.

/etc/X11/xdm/Xservers

This file simply maps the name of a display with an X server. For example display :0 is

understood

to be the local X server. Remember that X always runs on the first free /dev/tty.

/etc/X11/xdm/xdm-config

This is the main configuration file for xdm. It is also used to enable XDMCP (see exercises)

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/etc/X11/xdm/Xaccess

This file is used to enable XDMCP, allowing remote hosts to directly connect to the local server

( using -query) or query about other display

The Xaccess file

# $XConsortium: Xaccess,v 1.5 91/08/26 11:52:51 rws Exp $

# Access control file for XDMCP connections

# To control Direct and Broadcast access:

# pattern

# To control Indirect queries:

# pattern list of hostnames and/or macros ...

# To use the chooser:

# pattern CHOOSER BROADCAST

# or

# pattern CHOOSER list of hostnames and/or macros ...

# To define macros:

# %name list of hosts ...

# The first form tells xdm which displays to respond to itself.

# The second form tells xdm to forward indirect queries from hosts matching

# the specified pattern to the indicated list of hosts.

# The third form tells xdm to handle indirect queries using the chooser;

# the chooser is directed to send its own queries out via the broadcast

# address and display the results on the terminal.

# The fourth form is similar to the third, except instead of using the

# broadcast address, it sends DirectQuerys to each of the hosts in the list

# In all cases, xdm uses the first entry which matches the terminal;

# for IndirectQuery messages only entries with right hand sides can

# match, for Direct and Broadcast Query messages, only entries without

# right hand sides can match.

* #any host can get a login window

# To hardwire a specific terminal to a specific host, you can

# leave the terminal sending indirect queries to this host, and

# use an entry of the form:

#terminal-a host-a

# The nicest way to run the chooser is to just ask it to broadcast

# requests to the network - that way new hosts show up automatically.

# Sometimes, however, the chooser can't figure out how to broadcast,

# so this may not work in all environments.

* CHOOSER BROADCAST #any indirect host can get a chooser

# If you'd prefer to configure the set of hosts each terminal sees,

# then just uncomment these lines (and comment the CHOOSER line above)

# and edit the %hostlist line as appropriate

#%hostlist host-a host-b

#* CHOOSER %hostlist #

The Xservers file

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# $XConsortium: Xserv.ws.cpp,v 1.3 93/09/28 14:30:30 gildea Exp $

# $XFree86: xc/programs/xdm/config/Xserv.ws.cpp,v 1.1.1.1.12.2 1998/10/04 15:23:14 hohndel Exp $

# Xservers file, workstation prototype

# This file should contain an entry to start the server on the

# local display; if you have more than one display (not screen),

# you can add entries to the list (one per line). If you also

# have some X terminals connected which do not support XDMCP,

# you can add them here as well. Each X terminal line should

# look like:

# XTerminalName:0 foreign

:0 local /usr/X11R6/bin/X

Since the Display Manager is also an x-application the Xrescources file is similar to the .Xrescources

file except that it controls how the login screen is displayed .

Sample Xrescources file

! $XConsortium: Xresources /main/8 1996/11/11 09:24:46 swick $

xlogin*borderWidth: 3

xlogin*greeting: CLIENTHOST

xlogin*namePrompt: login:\040

xlogin*fail: Login incorrect

#ifdef COLOR

xlogin*greetColor: CadetBlue

xlogin*failColor: red

*Foreground: black

*Background: #fffff0

#else

xlogin*Foreground: black

xlogin*Background: white

#endif

XConsole.text.geometry: 480x130

XConsole.verbose: true

XConsole*iconic: true

XConsole*font: fixed

Sample xdm-config file

! $XFree86: xc/programs/xdm/config/xdm-conf.cpp,v 1.1.1.2.4.2 1999/10/12 18:33:29 hohndel Exp $

DisplayManager.servers: /etc/X11/xdm/Xservers

DisplayManager.accessFile: /etc/X11/xdm/Xaccess

! All displays should use authorization, but we cannot be sure

! X terminals will be configured that way, so by default

! use authorization only for local displays :0, :1, etc.

DisplayManager._0.authorize: true

DisplayManager._1.authorize: true

DisplayManager*resources: /etc/X11/xdm/Xresources

DisplayManager*session: /etc/X11/xdm/Xsession

DisplayManager*authComplain: false

! SECURITY: do not listen for XDMCP or Chooser requests

! Comment out this line if you want to manage X terminals with xdm

DisplayManager.requestPort: 0

6. Troubleshooting X Clients

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The X Environment

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Occasionally X Clients wont terminate properly leaving zombie processes. A zombie process in one

whose parent processes has terminated, and cannot clear references to the child process. When a child

process’ parent exits leaving the child process still running, this is usually visible by running ps which will

reveal the child process being owned by PID 1 (init). These processes should be killed because they may

be using CPU resources. Killing such a process requires the user to be the user who owns the process,

or root. It might be necessary to use the –9 option to actually kill these processes.

7. Choosing a Window Manager

The area that is commonly referred to as the desktop is also known in the X Window world as the

screen. It covers the entire area of your monitor display. The root window is the background of your

screen, typically used to display a colour or picture. The window manager provides an interface between

the user and the X server. It is virtually impossible to use X without a window manager, because it

provides the title bar and the familiar buttons with which you manipulate the display.

Information on available window managers is available from the Window Managers website at

http://www.PliG.org/xwinman. Many of the Linux versions of these window managers are available at

ftp://metalab.unc.e du /pub/Linux/X11/window-managers .

In addition to the various window managers there are also various desktop environments, among which

the most common are KDE and GNOME.

The most common window managers are listed below:

fvwm

icewm

amiWM

mlvwm

dfm

olwm

olvwm

mwm

Window Maker

AfterStep

Enlightenment

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9. Exercises

Before starting make sure you are running in runlevel 3.

init 3

1. Log into a virtual terminal (e.g Alt+F1)

2. As root save the existing configuration file /etc/X11/XF86Config and try out the various configuration

tools:

Redhat: Xconfigurator, redhat-config-xfree86 (8.0)

Mandrake : XFdrake

Suse: sax

XF86Setup

xf86config

X (this is the X11 server itself, use the -configure flag)

3. Start the X server by typing X. This will start X11R6 alone with no window managers. Return to a

virtual terminal (e.g Ctrl+Alt+F2) and get the command line back. Then do the following:

export DISPLAY=localhost:0

xterm&

Go back into X by typing Ctrl+Alt+F7 (if you haven’t changed the defaults in /etc/inittab...). You should

have an xterminal running. Next type in this terminal:

twm&

What has happened? Can you kill twm without killing X? Go back to a

virtual terminal (e.g Ctrl+Alt+F2) and type:

X :1

Log into another virtual terminal (e.g tty3) and type:

export DISPLAY=:1; xterm&

You now have two X servers running on screen 0 and 1. How do you switch from one to another?

4. Setting up XDMCP

For this to work make sure the line containing an ‘*’ is uncommented in /etc/X11/xdm/Xaccess.

If you are using xdm or kdm comment out the line in xdm-config as follows

!DisplayManager.requestPort: 0

This line is originally uncommented and allows only local login requests on screen 0 (more secure).

If you are using gdm then you will also need to edit gdm.conf and put

enable=true

This will turn off the default security settings for gdm.

If your IP is 1.2.3.4 then users on your network can start an X session with:

X –query 1.2.3.4 :1

X -indirect 1.2.3.4 :1

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Appendix

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Page 99

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