Linux Introduction

Linux Introduction

What are the benefits of Linux?

A modern, very stable, multi-user, multitasking environment

Unsurpassed computing power, portability, and flexibility

Excellent networking capability Hundreds of specialized applications Freedom from viruses A platform which will technically develop at a

rapid pace Linux runs on many hardware platforms

File System: Filenames

Linux is case-sensitive. Filenames under Linux can be up to 256 characters long Contain letters, numbers, ".“ (dots), "_" (underscores) and "-"

(dashes) Not possible to have '/' (slash) as a part of the filename Not recommended to use special metacharacters: "*" (asterisk),

"?" (question mark), " “ (space), "$" (dollar sign), "&" (ampersand), any brackets

* = Matches any sequence of zero or more characters, except for "." (a dot) at the beginning of a filename.

? = Matches any single character. [abC1] = Matches a single character in the enumerated set. In this example

the set contains: 'a', 'b', 'C', and '1'. [a-z] = Matches any lower-case letter. [A-F] = Matches any upper-case letter from A to F. [0-9] = Matches any single digit. [a-zA-Z0-9] = Matches any letter (lower or upper case) or any digit.

File System: Basic Directories

The root "/" contains basic operating system and maintenance tools.

/usr contains all commands, libraries, documentation, and major

applications /var

contains files that change: spool directories, log files, lock files, temporary files, and formatted manual pages.

/home contains user files (users' own settings, customization files,

documents, data, mail, caches, etc). /proc

access to information about the system stored in the memory (they don't really exist on the disk)


The parts of the root filesystem are: /bin--executables (binaries) needed during

bootup that might be used by normal users /sbin--executables (system binaries) not

intended for use by general users /etc--system-wide configuration files /root--the home directory of the system

administrator (called super-user or root) /dev--hardware device files.


Other parts of the root filesystem: /mnt--mount points for removable media

(floppy, cdrom, zipdrive), partitions of other operating systems, network shares

/lib--shared libraries for programs that reside on the root filesystem and kernel modules.

/boot--files used by the bootstrap loader /tmp--temporary files.


Other parts of the root filesystem: /usr/share --Data independent from computer

architecture /usr/bin and /usr/sbin --similar to their equivalents

on the root filesystem (/bin and /sbin), but not needed for basic bootup. Most commands will reside here.

/usr/local/bin --perhaps smaller "user"-installed executables, plus symbolic links to the larger executables contained in separate subdirectories under /usr/local

Command “mkdir” is used to create directories mkdir /mnt/cdrom


Swap space is an extension of the physical memory of the computer

Usually one is created at installation Other swap partitions can be created and formatted

mkswap /dev/hda4

Swap space can be enabled/disabled swapon /dev/hda4 swapoff /dev/hda4

Temporary swap: Create a file with the size of your swap file: dd if=/dev/zero of=/swapfile bs=1024 count=8192 mkswap /swapfile 8192 swapon /swapfile swapoff /swapfile rm /swapfil

Running Programs and Commands

Programs are executables binary files To run a program:

It must be in your PATH or use its full path and name (Ex: /bin/date)

It must have Execute permissions set by owner Programs in the current directory are run by:./program_name

Most commands accept numerous "options". An option can be introduced with an "-" (dash). For example:ls –l –a OR ls -la

Running Programs and Commands

The PATH is the list of directories which are searched when you request the execution of a program

You can check your PATH using this command:echo $PATH

Which returns something like:/opt/kde/bin:/usr/local/bin:/bin:/usr/bin:/usr/X11R6/bin:/home/yogin/bin

To set the PATH of a user, edit the profile file:/home/user_login_name/.bash_profile

to add something like:PATH="$PATH:$HOME/bin:"."

export PATH

Aliases can be created for long and hard to remember commandsalias cdrom="mount -v /mnt/cdrom"

Users, passwords, file permissions

The “root” account is the super-user administrating account normal users (non-root) can write to their home directory (created with

their accounts) only (almost)/home/user_login_name

A user account can be created by "root"adduser joe

passwd joe

[type the password for the user joe]

[retype the password for the user joe] user changes his/her password

passwd

(current) UNIX password: pass_OLD

New UNIX password: pass_NEW

Retype New UNIX password: pass_NEW


Groups of users can be created A user can be a member of one or more

groups Each file (or directory) belongs to an owner

and to a group The owner is typically the person who created

(or copied) the file. Permissions on file usage (r, w, x) are set by

the owner for file users: owner (u), group (g), other users (o), and all (a).


“ls –l” command lists the files and their permissionsdrwxr-xr-x 2 root root 21504 Apr 24 19:27 dev

Command “chmod” is used to change file permissions. chmod a+r junk chmod o-x junk

Instead of letters, one can also use numbers to specify the permissions execute=1, write=2, read=4, 0= no permission The total permission for a class of users is the sum of the three chmod 770 junk

For directories: r=permission to list the filenames in the directory, w=permission to create or delete files in the directory, and x=permission to access the directory


Default permissions on new files are set by command “umask” umask u=rw,g=,o= umask 077 (numbers for permissions taken away

not granted) “suid” on executables so that all users users

are given the "effective user id" of the file owner chmod a+s /usr/bin/xmms ls -l /usr/bin/xmms-rwsr-sr-x 1 root root 908k Feb 22 2000 /usr/bin/xmms

Shells

A shell is the program that interprets what you type on the command line and decides what to do with it

There are several shells available on the Linux system bash ("Bourne Again“ shell) – default shell sh (Bourne shell, standard on many UNIX systems) csh (C shell, with a syntax akin to the "c“ programming language, available on most

UNIX systems) pdksh (public domain Korn shell) tcsh (tiny C shell, often used on small systems) sash (stand-alone shell, could be used when libraries are not available)

You can determine the shell you are running using: echo $SHELL

To change the shell: tcsh bash exit

Shells To display shell prompt:

echo $PS1

To set the prompt: PS1="[\u@\h \W]\$ "

Fields of the prompt: \u - username of the current user (= $LOGNAME), \h - the name of the computer running the shell (hostname), \H - entire hostname, \W - the base of the name of the of the current working directory, \w - the full name of the current working directory, \$ - display "$" for normal users and "#" for the root, \! - history number of the current command, \# - number of the current command (as executed in the current shell), \d - current date, \t - current time (24-hr), \T - current time (12-hr) - bash 2.0 only, \@ - current time (AM/PM format) - bash 2.0 only, \s - name of the shell, \a - sound alarm (beep), \j - number of jobs the user has, \n - new line, \\ - backslash, \[ - begin a sequence of non-printable characters, \] - end a sequence of non-printable characters, \nnn - the ASCII character corresponding to the octal number nnn. $(date) - output from the date command (or any other command for that matter)

Accessing Drives

“mount” command adds directories and files from a device to the Linux directory

mount the CDROM with a command (as root) mount -t auto /dev/cdrom /mnt/cdrom /dev/cdrom should exist first If this works, the contents of the CD appears in the

directory /mnt/cdrom To unmount a mounted CD, exit the

directory /mnt/cdrom and type as root: umount /mnt/cdrom

Accessing Drives

A short listing of possible drives could include: hda -- the master drive on the first IDE interface (that's always

the first hard drive) hdb -- the slave drive on the first IDE interface (you must have

at least two hard drives for that) hdc -- the master drive on the second IDE interface (if you

have two IDE interfaces on your computer, most newer computers do)

hdd -- the slave drive on the second IDE interface (if you have one)

sda -- the first SCSI drive sdb -- the second scsi drive ("sdc" is the third scsi drive, etc.

There can be many scsi drive on a system). USB and parallel devices are handled SCSI devices

Accessing Drives

Mounting DOS/Windows FAT partition mount -t vfat /dev/hda1 /mnt/dosdrive

To mount so that all the users can read and write mount -t vfat -o user,rw,exec,umask=000 /dev/hda1

/mnt/dosdrive Mounting from Network File System (NFS)

mount -t nfs mars:/home /mnt/mars_home For automount, the mount commands are

added to the the file /etc/fstab

Working with X-windows

GUI is provided through X-servers (XF86) Two major GUI desktop packages available as

options on installations: KDE and GNOME KDE programs can be run under GNOME and

vice versa, KDE is older, more solid, more power requiring GNOME is lighter but less stable Default display is number 0

Working with X-windows

Switching between text and graphics modes <Ctrl><Alt><F1> to <Ctrl><Alt><F6> for a total of 6 text

consoles <Ctrl><Alt><F7> to <Ctrl><Alt><F11> for a total of 5 graphics

consoles

To start the X-server startx &

OR init 5

To start KDE or GNOME Startkde gnome-session

Some Essential Keyboard Shortcuts

<Tab> Autocomplete the command if there is only one option, or else show all the available options

<ArrowUp> Scroll back and edit the command history

<Shift><PgUp> Scroll terminal output up <Ctrl><Alt><Esc> Kill the window to be clicked with

mouse pointer <Ctrl><Alt><BkSpc> Kill the current X-windows

server <Ctrl><Alt><Del> Shut down the system and reboot. <Ctrl>c Kill the current program

Getting Help on Commands

any_command --help |more Display a brief help on a command (works with most commands).

man topic Display the contents of the system manual pages (help) on the topic. Press "q" to quit the viewer.

info topic Display the contents of the info on a particular command.

apropos topic Give the list of the commands that have something to do with a topic.

whatis topic Give a short list of commands matching a topic. Searches keywords only.

help command Display brief info on a bash (shell) built-in command

Some Basic Commands

pwd Print working directory, i.e., display the name of my current directory on the screen

whoami Print my login name date Print the operating system current date, time and timezone. date 123123572000 Change the date and time to 2000-12-31

23:57 time Determine the amount of time that it takes for a process to

complete (eg., time ls) history | more Show the last (1000 or so) commands executed

from the command line on the current account. df –h (=disk free) Print disk info about all the filesystems (in

human-readable form). du / -bh | more (=disk usage) Print detailed disk usage for each

subdirectory starting at the "/" (root) directory (in human legible form)

Some Basic Commands

~ is the home directory of the user ls OR dir List the contents of the current directory.

ls –al List the content of the current directory, all files (also those starting with a dot) with all details

cd directory_name Change directory. cd - will take you to your previous directory cd .. will take me one directory up

cp source destination Copy files. cp /home/stan/existing_file_name . Copy a file to the current working

directory. -R option (stands for "recursive") to copy the contents of whole directory

trees, mv source destination Move or rename files or directories ln source destination Create a hard link called destination to the file called

source ln -s source destination Create a symbolic (soft) link called "destination" to the

file called "source"

Some Basic Commands

rm files Remove (delete) files -f (=force) Delete without confirmation rm -r files (recursive remove) Remove files,

directories, and their subdirectories. mkdir directory_name Make a new directory. cat filename View the content of a text file

called "filename“ cat filename | more one page a time. cat filename | less OR less filename Scroll a

content of a text file. Press q when done.

Documents

Linux Introduction