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Introduction to Linux

Colin Jamison

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Help on Unix Commands

• List all options available for a command and also some example usage e.g.

• man command-name

• As for ‘man’ but the ‘info’ command has more information and is up to date e.g.

• info command-name

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UNIX Command Formatcommand <options> <arguments>

• The first word is the command

• Options follow commands

• Commands/options/arguments are case sensitive

• A command may or may not have options

$ ls

$ ls -al• Arguments are normally files/directories

$ ls -al /etc

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Directory and File Names

• Case sensitive

• Any character

• Avoid “ / * > space ! ”

– they are legal but their use is problematic with shells

• Must be unique inside its directory

• Wildcard

– * any number of characters

– ? any single character

– [ ] Any one of the characters inserted between the brackets

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Path Names

• Path name - is an address that uniquely identifies a file or directory in the UNIX file system.

• Absolute path name - always starts from the root directory e.g. /usr/local/bin

• Relative path name - path relative to the present working directory e.g. if pwd is /usr relative pathname local/bin is equivalent to the absolute pathname /usr/local/bin

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Directory Navigation

• Changing directory

$ cd /usr

$ cd local/bin

$ cd ..• Present directory

$ pwd

/home/cjamison/• Creating/removing directories

$ mkdir directoryname

$ rmdir directoryname

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Directory Contents

• File listing

$ ls - abbreviated list

$ ls -a - abbreviated list + hidden files

$ ls -al - long list + hidden files

$ ls -F - abbreviated list + file type

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bash2.04$ ls -ltotaldrwxr-xr-x 1 cjamison staff 123 Dec 12 2003 Aproject-rwx--x--x 1 cjamison staff 514 Dec 24 2003 Ascript-rwxr--r-- 1 cjamison staff 2345 Jan 02 2004 afile-rwxr--r-- 1 cjamison staff 231 Aug 12 2003 checksum-rwxr-x--x 1 cjamison staff 126 Dec 24 1990 dos2unix-rwx------ 1 cjamison staff 732 Oct 23 2003 dev.txt-rwxr-x--x 1 cjamison staff 9470 Aug 26 2003 excaliburdrwxr-x--x 1 cjamison staff 512 Dec 10 2003 homedrwx------ 1 cjamison staff 512 Jan 16 2004 mp3drwx------ 1 cjamison staff 512 Sep 01 2003 payroll-rwxr-x--- 1 cjamison staff 8972 Aug 21 2003 swallow -rw------- 1 cjamison staff 42 Dec 24 2003 swift.txtbash2.04$

File listing

type

access permission

owner

group

sizedate and timelast modified

name

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Access Permissions

• Access permissions on a directory determine whether a file in the directory can be renamed or removed

• File permissions determine what can be done to the file contents

• To allow access to a directory, access permissions should be set for all of its parent directories all the way up to the root directory

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Access Permissions• The first character indicates the type of file:

– directory (d) – link (l)– plain file (-)

-rwxrwxr-x-rwxrwxr-x The rest, specify three types of users

owner group others

who are allowed to (r) read (w) write (x) execute

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Numerical Access Permissions

-|rwx|r-x|r--|

|111 |101|100|

Character

Binary

Octal | 7 | 5 | 4 |

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Protecting Your Files

• -r-- --- --- (400) protect it from accidental editing

• -rw- --- --- (600) owner can edit/read the file

• -rw- r-- r-- (644) owner can edit, others may read

• -rw- rw- rw- (666) everyone can edit/read

• dr-x r-x r-x (555) everyone can list but can’t create delete/rename files

• drwx --- --- (700) owner can do anything

• drwx r-x r-x (755) owner can do anything, others can read

• drwx rwx rwx (777) anyone can edit/read/run

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Changing Access Permissionschmod permission files

• Character Method

$ chmod a=r-x filename

$ chmod u=rwx filename

$ chmod go+r filename

$ chmod ugo-w filename• Numerical Method

$ chmod 755 filename

$ chmod 600 filename

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Viewing and Editing Files

• Listing files– cat e.g. cat filename– tail e.g. tail -f filename

• Listing files one screen at a time– more e.g. cat filename | more

• Editing files– vi– emacs– GUI tools

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File Manipulation

• Copy – cp filename1 filename2

• move (rename)– mv filename directory

• remove (delete) - be careful!– rm filename

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Listing Processes

• List processes e.g.

• ps

• ps -ef

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Processes - Foreground v Background

• To run a process as a background process:

• process-name &

• To examine foreground/background processes use the jobs command

• fg

• bg

• Each process has a unique process id (PID)

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Disposing of Rogue Processes

• The kill command

• kill parameter PID

• parameters ‘-1’ to ‘-9’

• PID available from one of the process commands

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Redirection (1)

• ls -al > lsoutput1.txt

• ls -al >> lsoutput2.txt

• file descriptors

• standard input 0

• standard output 1

• standard error 2

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Redirection (2)

• Redirect standard error to a file• ls -al > lsout.txt 2>lserror.txt• redirect standard output and standard error to the same

file• ls -al > lsout.txt 2>&1• Redirecting input• more < lsout.txt• To discard standard output and standard error• ls -al > /dev/null 2>&1

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Pipes

• Simplify redirection e.g.

• ps | sort | more

• ps | grep ‘sh’ > listshells.txt

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‘C’ Tools (gcc)

• gcc - GNU C/C++ compiler• gcc filename1 … filenameX -o programfilename

• most commonly used options• [-Idir...] search dir for header files

• [-Ldir…] include dir to search for library ( -llibrary )

• [-o outfile]

• [-ggdb] include gdb debugging information

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‘C’ Tools (gdb)

• gdb - GNU debugger• gdb programfilename

• most commonly used options• run break [file:]function print expr

• next step c

• edit [file:]function list

• help command quit

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Questions ?