GNU Free Documentation License

Version 1.2, November 2002

0. PREAMBLE

The purpose of this License is to make a manual, textbook, or other functional and useful document "free" in the sense of freedom: to assure everyone the effective freedom to copy and redistribute it, with or without modifying it, either commercially or noncommercially. Secondarily, this License preserves for the author and publisher a way to get credit for their work, while not being considered responsible for modifications made by others.

This License is a kind of "copyleft", which means that derivative works of the document must themselves be free in the same sense. It complements the GNU General Public License, which is a copyleft license designed for free software.

We have designed this License in order to use it for manuals for free software, because free software needs free documentation: a free program should come with manuals providing the same freedoms that the software does. But this License is not limited to software manuals; it can be used for any textual work, regardless of subject matter or whether it is published as a printed book. We recommend this License principally for works whose purpose is instruction or reference.

1. APPLICABILITY AND DEFINITIONS

This License applies to any manual or other work, in any medium, that contains a notice placed by the copyright holder saying it can be distributed under the terms of this License. Such a notice grants a world-wide, royalty-free license, unlimited in duration, to use that work under the conditions stated herein. The "Document", below, refers to any such manual or work. Any member of the public is a licensee, and is addressed as "you". You accept the license if you copy, modify or distribute the work in a way requiring permission under copyright law.

A "Modified Version" of the Document means any work containing the Document or a portion of it, either copied verbatim, or with modifications and/or translated into another language.

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The "Invariant Sections" are certain Secondary Sections whose titles are designated, as being those of Invariant Sections, in the notice that says that the Document is released under this License. If a section does not fit the above definition of Secondary then it is not allowed to be designated as Invariant. The Document may contain zero Invariant Sections. If the Document does not identify any Invariant Sections then there are none.

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The Document may include Warranty Disclaimers next to the notice which states that this License applies to the Document. These Warranty Disclaimers are considered to be included by reference in this License, but only as regards disclaiming warranties: any other implication that these Warranty Disclaimers may have is void and has no effect on the meaning of this License.

2. VERBATIM COPYING

You may copy and distribute the Document in any medium, either commercially or noncommercially, provided that this License, the copyright notices, and the license notice saying this License applies to the Document are reproduced in all copies, and that you add no other conditions whatsoever to those of this License. You may not use technical measures to obstruct or control the reading or further copying of the copies you make or distribute. However, you may accept compensation in exchange for copies. If you distribute a large enough number of copies you must also follow the conditions in section 3.

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3. COPYING IN QUANTITY

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4. MODIFICATIONS

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• A. Use in the Title Page (and on the covers, if any) a title distinct from that of the Document, and from those of previous versions (which should, if there were any, be listed in the History section of the Document). You may use the same title as a previous version if the original publisher of that version gives permission.

• B. List on the Title Page, as authors, one or more persons or entities responsible for authorship of the modifications in the Modified Version, together with at least five of the principal authors of the Document (all of its principal authors, if it has fewer than five), unless they release you from this requirement.

• C. State on the Title page the name of the publisher of the Modified Version, as the publisher.

• D. Preserve all the copyright notices of the Document.

• E. Add an appropriate copyright notice for your modifications adjacent to the other copyright notices.

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• G. Preserve in that license notice the full lists of Invariant Sections and required Cover Texts given in the Document's license notice.

• H. Include an unaltered copy of this License.

• I. Preserve the section Entitled "History", Preserve its Title, and add to it an item stating at least the title, year, new authors, and publisher of the Modified Version as given on the Title Page. If there is no section Entitled "History" in the Document, create one stating the title, year, authors, and publisher of the Document as given on its Title Page, then add an item describing the Modified Version as stated in the previous sentence.

• J. Preserve the network location, if any, given in the Document for public access to a Transparent copy of the Document, and likewise the network locations given in the Document for previous versions it was based on. These may be placed in the "History" section. You may omit a network location for a work that was published at least four years before the Document itself, or if the original publisher of the version it refers to gives permission.

• K. For any section Entitled "Acknowledgements" or "Dedications", Preserve the Title of the section, and preserve in the section all the substance and tone of each of the contributor acknowledgements and/or dedications given therein.

• L. Preserve all the Invariant Sections of the Document, unaltered in their text and in their titles. Section numbers or the equivalent are not considered part of the section titles.

• M. Delete any section Entitled "Endorsements". Such a section may not be included in the Modified Version.

• N. Do not retitle any existing section to be Entitled "Endorsements" or to conflict in title with any Invariant Section.

• O. Preserve any Warranty Disclaimers.

If the Modified Version includes new front-matter sections or appendices that qualify as Secondary Sections and contain no material copied from the Document, you may at your option designate some or all of these sections as invariant. To do this, add their titles to the list of Invariant Sections in the Modified Version's license notice. These titles must be distinct from any other section titles.

You may add a section Entitled "Endorsements", provided it contains nothing but endorsements of your Modified Version by various parties--for example, statements of peer review or that the text has been approved by an organization as the authoritative definition of a standard.

You may add a passage of up to five words as a Front-Cover Text, and a passage of up to 25 words as a Back-Cover Text, to the end of the list of Cover Texts in the Modified Version. Only one passage of Front-Cover Text and one of Back-Cover Text may be added by (or through arrangements made by) any one entity. If the Document already includes a cover text for the same cover, previously added by you or by arrangement made by the same entity you are acting on behalf of, you may not add another; but you may replace the old one, on explicit permission from the previous publisher that added the old one.

The author(s) and publisher(s) of the Document do not by this License give permission to use their names for publicity for or to assert or imply endorsement of any Modified Version.

5. COMBINING DOCUMENTS

You may combine the Document with other documents released under this License, under the terms defined in section 4 above for modified versions, provided that you include in the combination all of the Invariant Sections of all of the original documents, unmodified, and list them all as Invariant Sections of your combined work in its license notice, and that you preserve all their Warranty Disclaimers.

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In the combination, you must combine any sections Entitled "History" in the various original documents, forming one section Entitled "History"; likewise combine any sections Entitled "Acknowledgements", and any sections Entitled "Dedications". You must delete all sections Entitled "Endorsements."

6. COLLECTIONS OF DOCUMENTS

You may make a collection consisting of the Document and other documents released under this License, and replace the individual copies of this License in the various documents with a single copy that is included in the collection, provided that you follow the rules of this License for verbatim copying of each of the documents in all other respects.

You may extract a single document from such a collection, and distribute it individually under this License, provided you insert a copy of this License into the extracted document, and follow this License in all other respects regarding verbatim copying of that document.

7. AGGREGATION WITH INDEPENDENT WORKS

A compilation of the Document or its derivatives with other separate and independent documents or works, in or on a volume of a storage or distribution medium, is called an "aggregate" if the copyright resulting from the compilation is not used to limit the legal rights of the compilation's users beyond what the individual works permit. When the Document is included in an aggregate, this License does not apply to the other works in the aggregate which are not themselves derivative works of the Document.

If the Cover Text requirement of section 3 is applicable to these copies of the Document, then if the Document is less than one half of the entire aggregate, the Document's Cover Texts may be placed on covers that bracket the Document within the aggregate, or the electronic equivalent of covers if the Document is in electronic form. Otherwise they must appear on printed covers that bracket the whole aggregate.

8. TRANSLATION

Translation is considered a kind of modification, so you may distribute translations of the Document under the terms of section 4. Replacing Invariant Sections with translations requires special permission from their copyright holders, but you may include translations of some or all Invariant Sections in addition to the original versions of these Invariant Sections. You may include a translation of this License, and all the license notices in the Document, and any Warranty Disclaimers, provided that you also include the original English version of this License and the original versions of those notices and disclaimers. In case of a disagreement between the translation and the original version of this License or a notice or disclaimer, the original version will prevail.

If a section in the Document is Entitled "Acknowledgements", "Dedications", or "History", the requirement (section 4) to Preserve its Title (section 1) will typically require changing the actual title.

9. TERMINATION

You may not copy, modify, sublicense, or distribute the Document except as expressly provided for under this License. Any other attempt to copy, modify, sublicense or distribute the Document is void, and will automatically terminate your rights under this License. However, parties who have received copies, or rights, from you under this License will not have their licenses terminated so long as such parties remain in full compliance.

10. FUTURE REVISIONS OF THIS LICENSE

The Free Software Foundation may publish new, revised versions of the GNU Free Documentation License from time to time. Such new versions will be similar in spirit to the present version, but may differ in detail to address new problems or concerns. See http://www.gnu.org/copyleft/.

Each version of the License is given a distinguishing version number. If the Document specifies that a particular numbered version of this License "or any later version" applies to it, you have the option of following the terms and conditions either of that specified version or of any later version that has been published (not as a draft) by the Free Software Foundation. If the Document does not specify a version number of this License, you may choose any version ever published (not as a draft) by the Free Software Foundation.

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.

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

No Guarantee

The manual comes with no guarantee at all.

Resources

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

or

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

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

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

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:

packages: This directory contains the precompiled 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).

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

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.

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:

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.

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 partion of the computer's first IDE disk (/dev/hda5), the rescue disk script can then mount this resource on a subdirectoty of the filesystem in RAM, say /mnt/system. 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

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.
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

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.

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 C:\ drive. 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.

8. 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.

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 message 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.

Typical Resources

Manual Resourse Allocation

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 five classes:

• Display Devices
• Communication Devices
• Audio Devices
• Mass Storage Devices
• Human Interface Devices (HID)

The devices are pluuged 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 controlers:

4. SCSI Devices

Types of SCSI devices

There are two types ofSCSI interfaces:

- an 8-bit interface with a bus that supports 8 devices, this includes the controler, 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 controler, 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

A group of disks for example, using RAID is called a logical unit and is seen as a single device with a unique SCSI ID. To make the distinction between logical units a SCSI logical unit number or LUN is used.

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:

/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

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

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:

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.

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

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 runing on port 631.

When using cups lpd is replaced by the cupsd daemon.

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.

On the exam you may be asked questions on IRQ settings for devices such as the ethernet card, the parallel and the serial ports.

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:

• ramdisk
• fd
• 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.

Disk Partitions:

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

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 62 partitions (primary and logical, excluding the extended).

Typical output of fdisk -l

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.

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.

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.

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

3. Bootloaders

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.

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/rub.conf):

1. General/Global

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

timeout prompt timeout in seconds

2. Image

title name of the image

root where the 2^nd 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

4. Managed devices

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

The /etc/fstab format

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

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

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>

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.

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

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 can be enforced 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. 22 to reflect your system

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

The Linux Filesystem

1. The Filesystem Structure

A filesystem is similar to a tree structure. The root of the tree is always represented on 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.

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 /bin, /sbin, /etc and /lib must be subdirectories of root (/) and not mounted on separate partitions.

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”.

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

Let's 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:

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

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 name, user, group, permissions and time stamp of the associated data.

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 preformatted 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]

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 mounted as 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 of 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.

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 owners for each files and directories:

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:

Changing user owner and group owner:

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.

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

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).

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 should be 022.

This becomes clearer if you look at the following:

Permission arithmetics:

permission = standard permission – umask

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 shell script that executes a program and set the SUID of the script with chmod 4777 script or chmod u+s script.

Examples:

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 enables members of the group owner to create files with the appropriate group ownership (no need to use newgrp to change the effective group)

Examples:

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 causes the file or executable to be loaded into memory and causes 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.

Examples:

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 file on 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

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? ______________

9. Set the sticky-bit on the binary mozilla.

chmod o+t 'which mozilla`

Start mozilla twice and verify that the second time it will execute faster.

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`

Log in as another user and run xeyes. Then do:

ps aux | grep xeyes

(the binary should be running as root)

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.

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.

Executing a command using exec

The interactive shell is often refered to as the session leader and will be the parent process of any new process started from the shell which is then called a child process.

There are two methods available to execute a new command: exec and fork. By default a process will use the fork method. To force a process to use the exec method the command is preceeded by the exec command:

Notice that when xeyes is terminated the parent process will also exit. A useful example is a window manager started with exec in such a way that the X11 server will exit once the window manager is closed.

Full/Relative path

The shell interprets any string given on the command line as a command. If the string is a full path to an executable then the executable is started. If not (the command is a string) the 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

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

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.

Export, Set and Env:

There are two types of variable: local and global.

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

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

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

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

Special variables

The next few variables are related to process management.

3. Input, Output, Redirection

Any UNIX process has the ability to 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.

stdout redirection

program > file

The data flows from left to right.

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.

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:

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:

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.

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.

The ? wildcard replaces any one character.

Ranges

[ ] is used to define a range of value.

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

Quotes and escape codes

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

The backslash (\) is called an escape code cancels the meaning of all metacharacters and forces 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.

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.

5. The Command History

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

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.

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

Example

6. Other Commands

Aliases

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

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

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

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.

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:

Section "Files"
    RgbPath	"/usr/X11R6/lib/X11/rgb"
    FontPath   "/usr/X11R6/lib/X11/fonts/misc/"
    FontPath   "/usr/X11R6/lib/X11/fonts/75dpi/:unscaled"
    FontPath   "/usr/X11R6/lib/X11/fonts/100dpi/:unscaled"
    FontPath   "/usr/X11R6/lib/X11/fonts/Type1/"
    FontPath   "/usr/X11R6/lib/X11/fonts/Speedo/"
    FontPath   "/usr/X11R6/lib/X11/fonts/75dpi/"
    FontPath   "/usr/X11R6/lib/X11/fonts/100dpi/"
EndSection

Section "ServerFlags"
EndSection

Section "Keyboard"
    Protocol	"Standard"
    AutoRepeat	500 5
    XkbKeymap   "xfree86(us)"
EndSection

Section "Pointer"
    Protocol    "Microsoft"
    Device      "/dev/mouse"
    Emulate3Buttons
    Emulate3Timeout    50
EndSection

Section "Monitor"
    Identifier  "IBM 6091"
    VendorName  "IBM"
    ModelName   "6091"
    HorizSync   31.5 - 82.0
    VertRefresh 50-70

#640x480
ModeLine "640x480" 55.97 640  672  768  880 480  964  967 1003 -vsync -hsync
#1024x768
ModeLine "1024x768" 87.95 1024 1040 1128 1368 768  771  774  806 -vsync -hsync
#1280x1024
ModeLine "1280x1024"   105.00   1280 1380 1548 1680   1024 1024 1027 1049 -hsync -vsync

EndSection

Section "Device"
    Identifier  "Gemini P1"
    VendorName  "SI"
    BoardName   "P1"
    VideoRam    4096
    Clocks    55.97  63.00  57.27  105.00  40.03  44.94  50.11  65.03
EndSection

Section "Screen"
    Driver      "svga"
    Device      "Gemini P1"
    Monitor     "IBM 6091"
    DefaultColorDepth 16
    Subsection "Display"
        Depth       8
        Modes       "1280x1024"
        ViewPort    0 0
    EndSubsection
    Subsection "Display"
        Depth       16
        Modes       "1280x1024"
        ViewPort    0 0
    EndSubsection
    Subsection "Display"
        Depth       24
        Modes       "1280x1024"
        ViewPort    0 0
    EndSubsection
    Subsection "Display"
        Depth       32
        Modes       "1280x1024" "1024x768"
        ViewPort    0 0
    EndSubsection
EndSection

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