An Introduction to An Introduction to LinuxLinux

What is LinuxWhat is Linux A fully-networked 32/64-Bit A fully-networked 32/64-Bit Unix-like Unix-like Operating SystemOperating System

Unix Tools Like sed, awk, and grep Unix Tools Like sed, awk, and grep Compilers Like C, C++, FortranCompilers Like C, C++, Fortran

Network Tools Like telnet, ftp, ping, tracerouteNetwork Tools Like telnet, ftp, ping, traceroute Multi-user, Multitasking, MultiprocessorMulti-user, Multitasking, Multiprocessor Has the X Windows GUI Has the X Windows GUI

Runs on multiple platformsRuns on multiple platforms Includes the Source CodeIncludes the Source Code

Where did it come from?Where did it come from? Linus Torvalds created itLinus Torvalds created it

with assistance from programmers around the worldwith assistance from programmers around the world first posted on Internet in 1991first posted on Internet in 1991

Linux 1.0 in 1994; 2.2 in 1999Linux 1.0 in 1994; 2.2 in 1999 Today used on 7-10 million computersToday used on 7-10 million computers

with 1000’s of programmers working to enhance itwith 1000’s of programmers working to enhance it

Logging InLogging In login with account and password:login with account and password:

ubuntu login: uskudarliPassword:Last login: Tue Oct 15 10:13:13 from ubuntu[uskudarli@ubuntu uskudarli]$

Root Login!!!Root Login!!!

Do not login as root unless you have toDo not login as root unless you have to root is the system superuser root is the system superuser

Normal protection can be overriddenNormal protection can be overridden Careless use can cause damageCareless use can cause damage Has full access to everything by defaultHas full access to everything by default

root is the only user defined when you installroot is the only user defined when you install change root’s passwordchange root’s password define “regular” users for everyday usedefine “regular” users for everyday use

Creating a new userCreating a new user

Use the Use the useradduseradd command command Use the Use the passwdpasswd command to set password command to set password

[root@ubuntu]# useradd yildirim[root@ubuntu]# passwd yildirimChanging password for user yildirimNew UNIX password:Retype new UNIX password:passwd: all authentication tokens updated successfully[root@ubuntu]#

Adding a new userAdding a new user Limits on users can be controlled byLimits on users can be controlled by

QuotasQuotas ulimitulimit command command

Authority levels for a user controlled by Authority levels for a user controlled by groupgroup membershipmembership

Users and GroupsUsers and Groups

Users are identified by user identifications (UIDs)Users are identified by user identifications (UIDs) UIDs are associated with an integer [0 - 4 294 967 295UIDs are associated with an integer [0 - 4 294 967 295]]

(X� FFFFFFFF� ). (X� FFFFFFFF� ). Users with UID=0 have superuser privileges. Users with UID=0 have superuser privileges. Users are placed in groups, Users are placed in groups, Group have identifications (GIDs). Group have identifications (GIDs). Each GID is associated with an integer [0 to 4 294 967 Each GID is associated with an integer [0 to 4 294 967

295]295] System assigns UID (avoid duplicates)System assigns UID (avoid duplicates) Use Use idid to display your user and group information to display your user and group information

uid=300(uskudarli) gid=300(uskudarli) groups=300(uskudarli),3(sys),4(adm)

Users and GroupsUsers and Groups Groups define functional areas/responsibilitiesGroups define functional areas/responsibilities They allow a collection of users to share filesThey allow a collection of users to share files A user can belong to multiple groupsA user can belong to multiple groups You can see what groups you belong to using the You can see what groups you belong to using the groupsgroups command: command:

uskudarli sys adm

Typical Group SetupTypical Group Setup

sys bin adm staff

Using the new userUsing the new user Now logoff using the Now logoff using the exitexit command command login as the new userlogin as the new user

ubuntu login: uskudarliPassword:[uskudarli@ubuntu uskudarli]$

You need help?You need help? The Linux equivalent of HELP is The Linux equivalent of HELP is manman

(manual)(manual) Use Use man -k <keyword>man -k <keyword> : all commands with : all commands with

that keywordthat keyword Use Use man <command>man <command> : help for the command : help for the command Output is presented a page at a time. Output is presented a page at a time.

typetype b b to scroll backward to scroll backward ff or a or a spacespace to scroll forward to scroll forward qq to quit to quit

Unix StructureUnix Structure

More detailMore detail

User commands Shell

File Systems Kernel Device Drivers

Hardware

User commands includes executable programs and scripts

The shell interprets user commands.

The kernel manages the hardware resources for the

rest of the system.

Shells Shells

Several ‘shells’ available: Several ‘shells’ available: ksh,csh, bsh...ksh,csh, bsh... Linux Linux ==>==> bashbash Shell ScriptsShell Scripts

File SystemFile System

Hierarchical file systemHierarchical file system Data files are stored in Data files are stored in

directories (folders)directories (folders) Directories are nestedDirectories are nested

Root of hierarchyRoot of hierarchy / /

Directories

User home directories

Data Files

root

directory

Naming FilesNaming Files Files are named byFiles are named by

naming each directorynaming each directory starting at the rootstarting at the root

pathnamepathname

/home/amy/try

/etc/passwd

The Current DirectoryThe Current Directory

current (present) working current (present) working directorydirectory

pwdpwd returns value of returns value of current working current working directorydirectory

Current working directory

doc/letter./doc/letter/home/neale/doc/letter

Special File NamesSpecial File Names

Some file names are special:Some file names are special: // The root directory The root directory .. The current directory The current directory

.. .. The parent directoryThe parent directory ~~ My home directory My home directory

Examples:Examples: ./a ./a same as same as aa ../uskudarli/.bash../uskudarli/.bash go up one level search for go up one level search for

directory directory uskudarliuskudarli for for .bashrc.bashrc

Special FilesSpecial Files /home/home - all users’ home directories are stored here - all users’ home directories are stored here /bin/bin, , /usr/bin/usr/bin - system commands - system commands /sbin/sbin, , /usr/sbin/usr/sbin - commands used by sysadmins - commands used by sysadmins /etc/etc - all sorts of configuration files - all sorts of configuration files /var/var - logs, spool directories etc. - logs, spool directories etc. /dev/dev - device files - device files /proc/proc - special system files - special system files

Linux Command BasicsLinux Command Basics To execute a command, type its name and To execute a command, type its name and

arguments at the command linearguments at the command line

ls -l /etc

Command nameOptions(flags)

Arguments

Standard FilesStandard Files standard input standard input

input to commandinput to command default is the default is the terminalterminal

standard output standard output output of commandoutput of command default is the default is the terminalterminal

standard error standard error output for error messages output for error messages default is the terminaldefault is the terminal

standard input/outputstandard input/output

Redirecting OutputRedirecting Output The output of a command is sent to a fileThe output of a command is sent to a file

ls -l > out1“>” redirects to output file

Input RedirectionInput Redirection Contents of file1 become input to wc Contents of file1 become input to wc

wc < in1“<” redirects the file as input to wc

Connecting commands with Connecting commands with PipesPipes

The output of one command becomes the input The output of one command becomes the input of another command:of another command:

ps aux | grep ubuntu | wc -l

output of ps is sent to grep

grep searches for “ubuntu”

counts the lines and outputs to console

“|” separate processes

pipes – more examplespipes – more examples

ps -ef | grep group1ps -ef | grep group1(this shows all processes related with userid group1)(this shows all processes related with userid group1)

ps -ef | grep group1 | wc -lps -ef | grep group1 | wc -l

this will count the number of processes related with group1this will count the number of processes related with group1

Command OptionsCommand Options Command options allow you to control a Command options allow you to control a

command to a certain degreecommand to a certain degree Conventions:Conventions:

Usually being with a single dash and are a single Usually being with a single dash and are a single letter (“letter (“-l-l”)”)

Sometimes have double dashes followed by a Sometimes have double dashes followed by a keyword (“keyword (“--help--help”)”)

Sometimes follow no pattern at allSometimes follow no pattern at all

Common CommandsCommon Commands pwdpwd - print (display) the working directory - print (display) the working directory cdcd <<dir>dir> - change the current working directory to - change the current working directory to

dirdir lsls - list the files in the current working directory - list the files in the current working directory lsls -l -l - list the files in the current working directory - list the files in the current working directory

in long formatin long format

File CommandsFile Commands cpcp <fromfile> <tofile><fromfile> <tofile>

Copy from the <fromfile> to the <tofile> Copy from the <fromfile> to the <tofile> mvmv <fromfile> <tofile><fromfile> <tofile>

Move/rename the <fromfile> to the <tofile>Move/rename the <fromfile> to the <tofile> rmrm <file><file>

Remove the file named <file>Remove the file named <file> mkdirmkdir <newdir><newdir>

Make a new directory called <newdir>Make a new directory called <newdir> rmdirrmdir <dir><dir>

Remove an (empty) directoryRemove an (empty) directory

More CommandsMore Commands

whowho List who is currently logged on to the systemList who is currently logged on to the system

whoamiwhoami Report what user you are logged on asReport what user you are logged on as

psps List your processes on the systemList your processes on the system

ps auxps aux List all the processes on the systemList all the processes on the system

echo echo “Something to say…”“Something to say…” Echo a string to the terminalEcho a string to the terminal

More CommandsMore Commands

aliasalias - customize commands: - customize commands: alias del=rmalias del=rm alias grep=”grep -i”alias grep=”grep -i”

More CommandsMore Commands awkawk - - a file processing language a file processing language chownchown - - sets the user ID (UID) to owner for sets the user ID (UID) to owner for

the files and directories named by pathname the files and directories named by pathname arguments. arguments.

chown -R apache:httpd /usr/local/apache

More CommandsMore Commands diffdiff - determines the minimal set of - determines the minimal set of

changes needed to convert file1 to file2changes needed to convert file1 to file2 diff file1 file2diff file1 file2

findfind - - Searches a given file hierarchy specified Searches a given file hierarchy specified by path, finding files that match the criteria by path, finding files that match the criteria given by expressiongiven by expression

More CommandsMore Commands grepgrep -- Searches files for one or more pattern Searches files for one or more pattern

arguments. It does plain string, basic regular arguments. It does plain string, basic regular expression, and extended regular expression expression, and extended regular expression searchingsearching

find examplefind example find ./ -name "*.c" | xargs grep -i "fork"

find files with an extension “c” pass files to xargs•takes the names •constructs a command line of the form:

•grep -i fork <file1>…<filen>

•This command will search the files for the “fork”. •The “-i” flag makes the search case insensitive.

More CommandsMore Commands killkill - sends a signal to a process or process - sends a signal to a process or process

groupgroup You can only kill your own processes unless you You can only kill your own processes unless you

are rootare root

UID PID PPID C STIME TTY TIME CMDroot 6005 6692 2 14:34 ttyp0 00:00:00 sleep 10hroot 6716 6692 0 14:34 ttyp0 00:00:00 ps -ef[root@ubuntu log]# kill 6005[1]+ Terminated sleep 10h

More CommandsMore Commands

makemake – – manage projects containing a set of interdependent manage projects containing a set of interdependent

files files makemake keeps all such files up to date with one keeps all such files up to date with one

another: If one file changes, another: If one file changes, makemake updates all the updates all the other files that depend on the changed fileother files that depend on the changed file

More CommandsMore Commands

sedsed - - applies a set of editing subcommands applies a set of editing subcommands contained in a script to each argument input filecontained in a script to each argument input file

find ./ -name "*.c,v" | sed ’s/,v//g’ | xargs grep "PATH"

This finds all files in the current and subsequent directories with an extension of c,v. sed then strips the ,v off the results of the find command. xargs then uses the results of sed and builds a grep command which searches for occurrences of the word PATH in the C source files.

processesprocessesps -efps -ef

shows the processes that are running for this sessionshows the processes that are running for this session

More CommandsMore Commands tartar - manipulates archives - manipulates archives

An archive file that contains the complete contents An archive file that contains the complete contents of a set of other filesof a set of other files

preserves the directory hierarchy that contained the preserves the directory hierarchy that contained the original files. original files.

tar -tzf imap-4.7.tar.gzimap-4.7/imap-4.7/src/imap-4.7/src/c-client/imap-4.7/src/c-client/env.himap-4.7/src/c-client/fs.h

ShellsShells An interface between the Linux system and the An interface between the Linux system and the

useruser Used to call commands and programsUsed to call commands and programs An interpreterAn interpreter Powerful programming languagePowerful programming language Many available (bsh; ksh; csh; bash; tcsh)Many available (bsh; ksh; csh; bash; tcsh)

Another definition of a ShellAnother definition of a Shell

A shell is any program that A shell is any program that takes input from the usertakes input from the user translates it into instructions that the OS translates it into instructions that the OS

understandsunderstands presents the OS output to the user. presents the OS output to the user.

Why Shell?Why Shell?

Shell is Not Integral Part of OS Shell is Not Integral Part of OS UNIX is among first to separate UNIX is among first to separate Compare to MS-DOS, Mac, Win95, VM/CMSCompare to MS-DOS, Mac, Win95, VM/CMS GUI is NOT RequiredGUI is NOT Required Default Shell Can Be Configured Default Shell Can Be Configured

chsh -s /bin/bash chsh -s /bin/bash /etc/passwd/etc/passwd

Helps To Customize EnvironmentHelps To Customize Environment

#!/bin/bash#!/bin/bashwhilewhiletruetruedodo cat somefile > /dev/nullcat somefile > /dev/null echo .echo .donedone

Shell ScriptsShell Scripts

Switching UsersSwitching Users susu <accountname><accountname>

switch user accounts. switch user accounts. prompted for a password. prompted for a password. When this command completes, you will be logged into the When this command completes, you will be logged into the

new account. new account. Type Type exitexit to return to the previous account to return to the previous account

susu Switch to the root user account. Switch to the root user account. Warning: Use only when neededWarning: Use only when needed Note: Note: The root user does not need to enter a password when switching The root user does not need to enter a password when switching

users. It may become any user desired.users. It may become any user desired.

Environment VariablesEnvironment Variables

global settings for a shell and other Linux global settings for a shell and other Linux programs. programs.

global shell variablesglobal shell variables Setting:Setting:

VAR=/home/uskudarli/docVAR=/home/uskudarli/doc export TERM=vt100export TERM=vt100 SYSTEMNAME=`uname -n`SYSTEMNAME=`uname -n`

Environment VariablesEnvironment Variables

Using Environment Variables:Using Environment Variables: echo $VARecho $VAR cd $VARcd $VAR cd $HOMEcd $HOME echo “You are running on $SYSTEMNAME”echo “You are running on $SYSTEMNAME”

Displaying - use the following commands:Displaying - use the following commands: set set (displays local and environment variables)(displays local and environment variables) exportexport

Vars can be retrieved by a script or a programVars can be retrieved by a script or a program

Some Important Environment Some Important Environment VariablesVariables

HOMEHOME Your home directory Your home directory ~~

TERMTERM The type of terminal you are running The type of terminal you are running

PWDPWD Current working directoryCurrent working directory

PATHPATH List of directories to search for commandsList of directories to search for commands

PATH Environment VariablePATH Environment Variable

List of paths, where commands are searchedList of paths, where commands are searched PATH is a list of directory pathnames separated by PATH is a list of directory pathnames separated by

colons. colons. Example:Example: PATH=/bin:/usr/bin:/usr/X11R6/bin:/uPATH=/bin:/usr/bin:/usr/X11R6/bin:/usr/local/bin:/home/scully/binsr/local/bin:/home/scully/bin

If a command does not contain a slash, the shell tries If a command does not contain a slash, the shell tries finding the command in each directory in PATH. The finding the command in each directory in PATH. The first match is the command that will runfirst match is the command that will run

PATH Environment VariablePATH Environment Variable

Usually set in Usually set in /etc/profile /etc/profile May be modified in May be modified in ~/.profile~/.profile

File PermissionsFile Permissions Every file Every file

Is owned by someone Is owned by someone Belongs to a group Belongs to a group Has certain access permissions for owner, group, Has certain access permissions for owner, group,

and othersand others Default permissions determined by Default permissions determined by umaskumask

File PermissionsFile Permissions Every user:Every user:

Has a uid (login name)Has a uid (login name) gid (login group) gid (login group) membership of a "groups" list:membership of a "groups" list:

The The uiduid is who you are (name and number) is who you are (name and number) The The gidgid is your initial “login group” is your initial “login group” The The groups listgroups list is the file groups you can access via group is the file groups you can access via group

permissionspermissions

File PermissionsFile Permissions Linux provides three kinds of permissions:Linux provides three kinds of permissions:

ReadRead - read the file or list the directory - read the file or list the directory WriteWrite - write to the file or create new files to the - write to the file or create new files to the

directorydirectory ExecuteExecute - execute the file or lookup a specific file - execute the file or lookup a specific file

within a directorywithin a directory

File PermissionsFile Permissions The long version of a file listing (The long version of a file listing (ls -lls -l) ) displays the file permissions:displays the file permissions:

-rwxrwxr-x 1 uskudarli uskudarli 5224 Sep 30 03:22 hello-rw-rw-r-- 1 uskudarli uskudarli 221 Sep 30 03:59 hello.c-rw-rw-r-- 1 uskudarli uskudarli 1514 Sep 30 03:59 hello.sdrwxrwxr-x 7 uskudarli staff 1024 Sep 31 14:52 posixuft

Permissions

Owner

Group

Interpreting File PermissionsInterpreting File Permissions

-rwxrwxrwxOther permissions

Group permissions

Owner permissions

Directory flag (d=directory; l=link)

Changing File PermissionsChanging File Permissions Use the Use the chmodchmod command to change file command to change file

permissionspermissions The permissions are encoded as an octal numberThe permissions are encoded as an octal number

chmod 755 file # Owner=rwx Group=r-x Other=r-xchmod 500 file2 # Owner=r-x Group=--- Other=---chmod 644 file3 # Owner=rw- Group=r-- Other=r--

chmod +x file # Add execute permission to file for allchmod o-r file # Remove read permission for otherschmod a+w file # Add write permission for everyone

Links?Links? Links are references to files (aliases)Links are references to files (aliases) Two forms:Two forms:

HardHard SymbolicSymbolic

Can point to files on different physical devicesCan point to files on different physical devices Delete of original leaves link Delete of original leaves link Delete of link leaves originalDelete of link leaves original Can be created for directoriesCan be created for directories

Create using Create using lnln command command

PermissionsPermissions

All directories are special filesAll directories are special files The read/write/execute scheme is usedThe read/write/execute scheme is used

EditorsEditors

People are fanatical about their editorPeople are fanatical about their editor Several choices available:Several choices available:

vivi Standard UNIX editorStandard UNIX editor xeditxedit X windows text editorX windows text editor emacsemacs Extensible, Customizable Self-Extensible, Customizable Self-

Documenting Display EditorDocumenting Display Editor picopico Simple display-oriented text editor Simple display-oriented text editor

Linux Device HandlingLinux Device Handling

Devices are the way linux talks to the worldDevices are the way linux talks to the world Devices are special files in the Devices are special files in the /dev/dev directory (try directory (try ls /devls /dev))/dev/ttyx TTY devices/dev/hdb IDE hard drive/dev/hdb1 Partition 1 on the IDE hard drive/dev/mnda VM Minidisk /dev/dda Channel Attached DASD/dev/dda1 Partition 1 on DASD/dev/null The null device (“hole”)/dev/zero An endless stream of zeroes/dev/mouse Link to mouse (not /390)

PermissionsPermissions

All directories are special filesAll directories are special files The read/write/execute scheme is usedThe read/write/execute scheme is used

Devices and DriversDevices and Drivers Each Each /dev/dev file has a major and minor number file has a major and minor number

Major defines the device typeMajor defines the device type Minor defines device within that typeMinor defines device within that type Drivers register a device typeDrivers register a device type

brw-r--r-- 1 root root 64, 0 Jun 1 1999 /dev/mndacrw-r--r-- 1 root root 5, 0 Jan 5 09:18 /dev/tty

Major no. Minor no.Device Type: b - blockc - character

Special Files - /procSpecial Files - /proc Information about internal Linux processes are Information about internal Linux processes are

accessible to users via the accessible to users via the /proc/proc file system (in file system (in memory)memory)

/proc/cpuinfo CPU Information/proc/interrupts Interrupt usage/proc/version Kernel version/proc/modules Active modules

cat /proc/cpuinfovendor_id : IBM/S390# processors : 1bogomips per cpu: 86.83processor 0: version = FF, identification = 045226, machine = 9672

File SystemsFile Systems Linux supports many different typesLinux supports many different types Most commonly, ext2fsMost commonly, ext2fs

Filenames of 255 charactersFilenames of 255 characters File sizes up to 2GB File sizes up to 2GB Theoretical limit 4TBTheoretical limit 4TB

Derived from extfsDerived from extfs

File SystemsFile Systems mountmount

Mounts a file system froma device to the main file Mounts a file system froma device to the main file systemsystem

/etc/fstab/etc/fstab used to establish boot time used to establish boot time mountingmounting

Virtual File System (VFS)Virtual File System (VFS)

Logical file systemsLogical file systems compatibility with other O/S standards compatibility with other O/S standards portabilityportability VFS abstracts details of physical device and VFS abstracts details of physical device and

logical file system logical file system Processes access files using a common interface, Processes access files using a common interface,

without knowing what physical or logical system without knowing what physical or logical system of the fileof the file

Security GuidelinesSecurity Guidelines Take Care With Passwords Take Care With Passwords

Choose good passwords Choose good passwords Don't Use Real Words Don't Use Real Words Make Sure They Are Not Easily Guessed Make Sure They Are Not Easily Guessed Use Combinations Of Upper and Lower Case, Use Combinations Of Upper and Lower Case,

Numbers, Punctuation Numbers, Punctuation

Security GuidelinesSecurity Guidelines Restrict Superuser Access Restrict Superuser Access

Restrict where root can log in from Restrict where root can log in from /etc/securetty/etc/securetty restricts root access to devices listed restricts root access to devices listed

Use wheel group to restrict who can Use wheel group to restrict who can susu to root to root Put users who can Put users who can susu to root in wheel group to root in wheel group

in in /etc/group/etc/group file. file.

Security - Important FilesSecurity - Important Files

/etc/passwd - password file/etc/shpasswd - shadow password file/etc/group -lists groups and users contained in groups/etc/services - lists network services and their ports/etc/ftpusers - contains list of accounts that cannot use ftp/etc/hosts.equiv - generic list of remote users~/.rhosts - list of remote users for a specific account/etc/hosts - host definition list/etc/hosts.lpd - hosts who can use remote printing/etc/hosts.allow - lists services that remote users are allowed to use/etc/hosts.deny - lists services tthat remote users are not allowed to use/etc/nologin - no login message that also disables logins/etc/securetty - lists legal terminals for root to login from/etc/exports - lists locations that can be remotely accessed via NFS/etc/syslog.conf - configures the syslog facility/etc/inetd.conf - configures inetd

Three important tips:Three important tips:

ArrowsArrows Retrieve commands using Retrieve commands using ⇑⇑ or or ⇓⇓

ctrl-Cctrl-C stop programs at oncestop programs at once

cntl-Zcntl-Z execute process in backgroundexecute process in background

Additional ResourcesAdditional Resources UNIX Systems Administrator ResourcesUNIX Systems Administrator Resources

http://www.ugu.com/http://www.ugu.com/ Linux/390 Observations and Linux/390 Observations and NotesNotes

http://penguinvm.princeton.eduhttp://penguinvm.princeton.edu Introduction to LinuxIntroduction to Linux Linux Administration Made EasyLinux Administration Made Easy

http://www.linuxninja.com/linux-http://www.linuxninja.com/linux-admin/book1.htmladmin/book1.html

Additional ResourcesAdditional Resources http://http://www.linux.orgwww.linux.org http://www.tux.orghttp://www.tux.org http://www.li.orghttp://www.li.org www.linux.orgwww.linux.org www.be.itu.edu.tr/kaynak/kaynak/www.be.itu.edu.tr/kaynak/kaynak/ www.redhat.com www.redhat.com

More infoMore info

sunsite.bilkent.edu.tr sunsite.bilkent.edu.tr www.linuxfocus.org www.linuxfocus.org www.linas.org/Linux www.linas.org/Linux www.ext2.org www.ext2.org www.linuxhelp.org www.linuxhelp.org

www.linuxprogramming.org www.linuxprogramming.org www.linuxworld.com www.linuxworld.com www.linuxpowered.com www.linuxpowered.com www.linuxtoday.com www.linuxtoday.com www.linuxresources.com www.linuxresources.com www.kde.org www.kde.org www.caldera.com www.caldera.com www.debian.org www.debian.org www.gnome.org www.gnome.org portal.suse.com portal.suse.com www.kernel.org www.kernel.org www.linux.router.org www.linux.router.org