LINUX TUTORIAL - Gregg Roeten · 2019-02-16 · Linux Tutorial OS Bootloader kernel Daemons - background services, printing, sound, scheduling Shell Graphical Server = X or X server

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LINUX TUTORIAL ................................................................................................................................... 3

OS .......................................................................................................................................................................... 3

Releases ................................................................................................................................................................. 3

GUI or Command line Basics................................................................................................................................ 3

Networking Commands ......................................................................................................................................... 3

bash (Bourne again shell) ....................................................................................................................................... 4

Basic Navigation .................................................................................................................................................... 4

File Manipulation ................................................................................................................................................... 5

vi text editor .......................................................................................................................................................... 5

Wildcards ............................................................................................................................................................... 6

Permissions ........................................................................................................................................................... 6

Filters ..................................................................................................................................................................... 7 Run grep with extended regular expressions. ........................................................................................................... 8 Grep Regular Expression ........................................................................................................................................... 9

Regular Expressions ............................................................................................................................................... 9 Regular Expression Multipliers ................................................................................................................................ 10 Regular Expression Anchors .................................................................................................................................... 10

Piping and Redirection ......................................................................................................................................... 11

Process Management .......................................................................................................................................... 12

bash scripts .......................................................................................................................................................... 12 1. tar command examples ................................................................................................................................... 15 2. grep command examples ................................................................................................................................ 15 3. find command examples ................................................................................................................................. 16 4. ssh command examples .................................................................................................................................. 16 5. sed command examples .................................................................................................................................. 16 6. awk command examples ................................................................................................................................. 16 7. vim command examples ................................................................................................................................. 16 8. diff command examples .................................................................................................................................. 17 9. sort command examples ................................................................................................................................. 17 10. export command examples ........................................................................................................................... 17 11. xargs command examples ............................................................................................................................. 17 12. ls command examples ................................................................................................................................... 17 13. pwd command .............................................................................................................................................. 18 14. cd command examples ................................................................................................................................. 18 15. gzip command examples ............................................................................................................................... 18 16. bzip2 command examples ............................................................................................................................. 18 17. unzip command examples ............................................................................................................................ 18 18. shutdown command examples ..................................................................................................................... 19 19. ftp command examples ................................................................................................................................. 19 20. crontab command examples ......................................................................................................................... 19 21. service command examples .......................................................................................................................... 19 22. ps command examples .................................................................................................................................. 20 23. free command examples ............................................................................................................................... 20

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24. top command examples ................................................................................................................................ 20 25. df command examples .................................................................................................................................. 21 26. kill command examples ................................................................................................................................. 21 27. rm command examples ................................................................................................................................. 21 28. cp command examples ................................................................................................................................. 21 29. mv command examples ................................................................................................................................ 22 30. cat command examples ................................................................................................................................ 22 31. mount command examples .......................................................................................................................... 22 32. chmod command examples .......................................................................................................................... 22 33. chown command examples .......................................................................................................................... 23 34. passwd command examples ......................................................................................................................... 23 35. mkdir command examples ............................................................................................................................ 23 36. ifconfig command examples ......................................................................................................................... 23 37. uname command examples .......................................................................................................................... 23 38. whereis command examples ......................................................................................................................... 24 39. whatis command examples ........................................................................................................................... 24 40. locate command examples ........................................................................................................................... 24 41. man command examples .............................................................................................................................. 24 42. tail command examples ................................................................................................................................ 25 43. less command examples ............................................................................................................................... 25 44. su command examples .................................................................................................................................. 25 45. mysql command examples ............................................................................................................................ 26 46. yum command examples .............................................................................................................................. 26 47. rpm command examples ............................................................................................................................... 26 48. ping command examples .............................................................................................................................. 26 49. date command examples .............................................................................................................................. 26 50. wget command examples ............................................................................................................................. 27

hash command line for Linux. .............................................................................................................................. 28

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Linux Tutorial

OS Bootloader kernel Daemons - background services, printing, sound, scheduling Shell Graphical Server = X or X server Desktop Environment ex GNOME, Unity, have built-in file managers, web browsers, etc Applications

Releases Ubuntu - newbie friendly Debian or Fedora - above avg user Gentoo - master Ubuntu Server - server only distribution

GUI or Command line Basics Open a terminal on Linux WS

Applications -> System or Applications -> Utilities

Windows login into remote machine use SSH client, ex Putty which is free

Tab Completion works

Case Sensitive

file names with spaces allowed, will need quotes cd “Roman Holiday” OR

use escape character ie backslash \ ex cd Roman\ Holiday

Everything is a file, even directories If the GUI has locked up, and we are in luck, we can get to another console and kill the

offending process from there. To switch between consoles you use the keyboard sequence CTRL + ALT + F<Console>. So CTRL + ALT F2 will get you to a console (if all goes well) where you can run the commands as above to identify process ids and kill them. Then CTRL + ALT F7 will get you back to the GUI to see if it has been fixed.

! ls

executes last command ls command

!! execute last command

history | grep “keyword”

Networking Commands hostname -dfifinding host/domain name and IP address -

ping test network connection –

ifconfig gnetting network configuration –

netstat -all Network connections, routing tables, interface statistics –

nslookup query DNS lookup name – nslookup google.com

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telnetcommunicate with other hostname – telnet hostname port

traceroute outing steps that packets take to get to network host –

finger view user information –

telnet checking status of destination host -

ifconfigfind ws IP address

Description

bash is an sh-compatible command language interpreter that executes commands read from the

standard input or from a file. bash also incorporates useful features from the Korn and C shells

(ksh and csh).

bash is intended to be a conformant implementation of the Shell and Utilities portion of the

IEEE POSIX specification (IEEE Standard 1003.1). bash can be configured to be POSIX-

conformant by default.

bash (Bourne again shell) echo

prints to screen

echo #SHELL

/bin/bash

user@bash:

Basic Navigation

ls -l /home/ryan

ls

ls -ashows hidden files (.filename, dot before filename is a

hidden file)

ls Documents if in current directory relative path

ls /home/groeten/Documents absolute path

pwd

~ home

ls ~/Documents

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ls ./Documents current directory

ls ../Documents parent directory

ls ../../

cd Documents

cd ~/Documents

file.exe - an executable file, or program.

file.txt - a plain text file.

file.png, file.gif, file.jpg - an image.

man <command to look up>

File Manipulation mkdir [options] <dir>

rmdir

touch

cp [options] src dest

mv [options] src destcan also rename with mv command

rm [options] <file>

vi text editor vi filename

ZZ (Note: capitals) - Save and exit

:q! - discard all changes, since the last save, and exit

:w - save file but don't exit

:wq - again, save and exit

x - delete a single character

nx - delete n characters (eg 5x deletes five characters)

dd - delete the current line

dn - d followed by a movement command. Delete to where the movement command

would have taken you. (eg d5w means delete 5 words)

u - Undo the last action (you may keep pressing u to keep undoing)

U (Note: capital) - Undo all changes to the current line

cat <file>

less <file>

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less allows you to move up and down within a file using the arrow keys. You may go forward

a whole page using the SpaceBar or back a page by pressing b. When you are done you can

press q for quit.

Wildcards

* - represents zero or more characters

? - represents a single character

[] - represents a range of characters

ls [sv]*

range operator allows you to limit to a subset of characters. In this example we are looking for every file whose name either begins with a s or v.

ls *[0-9]*

With ranges we may also include a set by using a hyphen. So for example if we wanted

to find every file whose name includes a digit in it we could do the following:

ls [^a-k]*

We may also reverse a range using the caret ( ^ ) which means look for any character

which is not one of the following.

Permissions r read - you may view the contents of the file.

w write - you may change the contents of the file.

x execute - you may execute or run the file if it is a program or script.

owner - a single person who owns the file. (typically the person who created the file but ownership may be granted to some one else by certain users)

group - every file belongs to a single group.

others - everyone else who is not in the group or the owner.

view permissions use l option

ls -l

-rwxr----x

rwx owner read, write execute

-rwxr----x

r-- group read only

-rwxr----x

--x others execute only

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chmod g+wx filename

-rwxrwx--x

chmod go-x filename grp and other remove execute permission

-rwxrw----

chmod 777 read,write,execute for self,grp,others

SUID - Set User ID

Zeroth field - Special permissions, represents the special bits.

chmod 4750, 2777, 1477

"0" by default, which means: "No special permissions set."

Sticky bit = Value 1 = sets to directories - may only remove file in directory owned by you

Set Group id = Value 2 = execute as the Group of the file

Set User id= Value 4 = program is executed as the Owner of the file.

chmod 4750 = file may be executed by owner and grp and will be executed as the owner

Filters head

head filename prints entire file

head -r filename prints first 4 lines of file

tail

prints entire file or last x lines of file

sort

Sort will sort it's input, nice and simple. By default it will sort alphabetically but there are many options available to modify the sorting mechanism.

nl

number lines

nl -s '. ' -w 10 mysampledata.txt

format print

-s what should be printed after the number, dot and space

-w specifies how much padding to put before the numbers, 10

spaces in this example

1. Fred apples 20

2. Susy oranges 5

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3. Mark watermellons 12

4. Robert pears 4

5. Terry oranges 9

wc

word count

wc [options] path -w is # of words -l is # of lines

cut

sed

sed [expression] [path]

s/search/replace/g

substitute / what we’re searching for / what we’re to replace it with / global is optional

sed 's/oranges/bananas/g' mysampledata.txt

uniq [options] [path]

unique, remove duplicat lines from data. Dupes must be side by side

uniq mysampledata.txt

tac

reverse of cat!

grep

egrep or grep -E

Run grep with extended regular expressions. -IIgnore case (ie uppercase, lowercase letters).

-vReturn all lines which don't match the pattern.

-wSelect only matches that form whole words.

-cPrint a count of matching lines.

Can be combined with the -v option to print a count of non matchine lines.

-lPrint the name of each file which contains a match.

Normally used when grep is invoked with wildcards for the file argument.

-nPrint the line number before each line that matches.

-rRecursive, read all files in given directory and subdirectories.

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Grep Regular Expression .A single character

[abc]Range. ie any one of these characters

[^abc]Not range. A character that is not one of those enclosed.

(abc)Group these characters and remember for later.

\nReplace n with a number. Recall the charactes matched in that set of brackets.

May also be used to rename files or directories.

|The logical 'or' operation.

\In front of a character, removes it's special meaning.

egrep

egrep [command line options] <pattern> [path]

egrep is a program which will search a given set of data and print every line which contains a given pattern.

the -v option tells grep to instead print every line which does not match the pattern.

egrep 'mellon' mysampledata.txt

egrep -n 'mellon' mysampledata.txt -n print line #

-c line count of matches

egrep '[aeiou]{2,}' mysampledata.txt

identify any line with two or more vowels in a row. In the example below the multiplier {2,} applies to the preceding item which is the range.

egrep '2.+' mysampledata.txt

any line with a 2 on it which is not the end of the line. In this example the multiplier + applies to the . which is any character.

egrep 'or|is|go' mysampledata.txt

each line which contains either 'is' or 'go' or 'or'.

egrep '^[A-K]' mysampledata.txt

see orders for everyone who's name begins with A - K.

Regular Expressions . (dot)- a single character.

? - the preceding character matches 0 or 1 times only.

* - the preceding character matches 0 or more times.

+ - the preceding character matches 1 or more times.

{n} - the preceding character matches exactly n times.

{n,m} - the preceding character matches at least n times and not more than m times.

[agd] - the character is one of those included within the square brackets.

[^agd]- the character is not one of those included within the square brackets.

[c-f] - the dash within the square brackets operates as a range. In this case it means either

the letters c, d, e or f.

() - allows us to group several characters to behave as one.

| (pipe symbol) - the logical OR operation.

^ - matches the beginning of the line.

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# - matches the end of the line.

Regular Expression Multipliers ?The preceding item is optional, it is matched zero or one times.

* The preceding item will be matched zero or more times.

+The preceding item will be matched one or more times.

{n}The preceding item will be matched exactly n times.

{n,}The preceding item will be matched n or more times.

{n,m}The preceding item will be matched between n and m times.

Regular Expression Anchors ^From the beginning of the line.

#To the end of the line.

\<At the beginning of a word.

\>At the end of a word.

\bMatch either the beginning or end of a word.

Examples

egrep 'mellon' myfile.txt

Print every line in myfile.txt containing the string 'mellon'.

egrep -n 'mellon' myfile.txt

Same as above but print a line number before each line.

egrep '(.)bb\1' myfile.txt

Find every line with 2 b's and the same character both before and after those b's.

egrep -l '[0-9]{8,}' /files/projectx/*

Print each file in the directory projectx which contains a number of 8 digits or more.

egrep '\b[a-z0-9._%+-]+@[a-z0-9.-]+\.[a-z]{2,4}\b' myfile.txt

Print every line of myfiles.txt containing an email address.

Note: this is just a simple email matching pattern. There is a miniscule number of email addresses it will not match.

awk

data in record with field filter data and control how displayed like find and xargs popular alternative to Perl

awk '{print #2}' mysampledata.txtprint only the second column

scp

secure copy, part of SSH (Secure Shell)

copy files from one machine to another

scp [email protected]:/home/ryan/myfilex.jpg ./myfiley.jpg

diff

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Piping and Redirection STDIN (0) - Standard input (data fed into the program)

STDOUT (1) - Standard output (data printed by the program, defaults to the terminal)

STDERR (2) - Standard error (for error messages, also defaults to the terminal)

ls > myoutput

wc -l barry.txt > myoutput

ls >> myoutput

wc -l < myoutput

( < ) then we can send data the other way. We will read data from the file and feed it into the program via it's STDIN stream.

wc -l < barry.txt > myoutput

cat myoutput

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Redirecting Standard Error

ls -l video.mpg blah.foo 2> errors.txt

-rwxr--r-- 1 ryan users 6 May 16 09:14 video.mpg

cat errors.txt

ls: cannot access blah.foo: No such file or directory

Piping

sending data from one program to another.

ls | head -3

barry.txt

bob

example.png

ls | head -3 | tail -1

example.png

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combine pipes and redirection too

ls | head -3 | tail -1 > myoutput

cat myoutput

example.png

Process Management ps -ef | grep ‘firefox’

kill

kill pid

kill -9 pid

CTRL +Z

jobs

fg move pgm from background to foreground

bg move pgm from foreground to background

bash scripts which

path to a program

which <program>

which bash

/bin/bash

which ls

/usr/bin/ls

#

placed before a var name referrs to its value

morevariables.sh

#!/bin/bash

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# A simple demonstration of variables

# Ryan 23/6/2015

echo My name is #0 and I’ve been give # # command line args

echo Here they are: #*

echo And the 2nd command line argument is #2

user@bash: ./morevariables.sh bob fred sally

My name is morevariables.sh and I’ve been given 3 command line args

Here they are: bob fred sally

And the 2nd command line argument is fred

if statements

if [ ] then else fi

ex projectbackup.sh

#!/bin/bash

# Backs up a single project directory

# Ryan 23/6/2015

if [ ## != 1 ]

then

echo Usage: A single argument which is the directory to backup

exit

fi

if [ ! -d ~/projects/#1 ]

then

echo The given dir does not seem to exist (possible typo?)

exit

fi

date=`date +%F`

# Do we already have a backup folder for todays date?

if [ -d ~/projectbackups/#1_#date ]

then

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echo This project has already been backed up today, overwrite?

read answer

if [ #answer != 'y' ]

then

exit

fi

else

mkdir ~/projectbackups/#1_#date

fi

cp -R ~/projects/#1 ~/projectbackups/#1_#date

echo Backup of #1 completed

Backup Script - Useful………………………….

projectbackup.sh

#!/bin/bash

# Backs up a single project directory

# Ryan 29/6/2015

date=`date +%F`

mkdir ~/projectbackups/#1_#date

cp -R ~/projects/#1 ~/projectbackups/#1_#date

echo Backup of #1 completed

./projectbackup.sh GRBackup

Backup of GRBackup completed

Cron

Command Run ON

mins hrs day-of-month months day-of-wk

30 3 * * 4 /bin/myscript.sh

Execute myscript.sh every Thursday at 3:30am.

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crontab -l

List of cron jobs running

Tar

Tape Archive

z = use gzip to compress

c = create new archive

v = verbose

f = result should be saved into a file

x = extract

tar -zcvf mytar.tar.gz *

50 Most Frequently Used UNIX / Linux

Commands (With Examples)

by Ramesh Natarajan on November 8, 2010

1. tar command examples

Create a new tar archive.

# tar cvf archive_name.tar dirname/

Extract from an existing tar archive.

# tar xvf archive_name.tar

View an existing tar archive.

# tar tvf archive_name.tar

2. grep command examples

Search for a given string in a file (case in-sensitive search).

# grep -i "the" demo_file

Print the matched line, along with the 3 lines after it.

# grep -A 3 -i "example" demo_text

Search for a given string in all files recursively

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# grep -r "ramesh" *

3. find command examples

Find files using file-name ( case in-sensitve find)

# find -iname "MyCProgram.c"

Execute commands on files found by the find command

# find -iname "MyCProgram.c" -exec md5sum {} \;

Find all empty files in home directory

# find ~ -empty

4. ssh command examples

Login to remote host

ssh -l jsmith remotehost.example.com

Debug ssh client

ssh -v -l jsmith remotehost.example.com

Display ssh client version

# ssh -V

OpenSSH_3.9p1, OpenSSL 0.9.7a Feb 19 2003

5. sed command examples

When you copy a DOS file to Unix, you could find \r\n in the end of each line. This example converts the DOS file format to Unix file format using sed command.

#sed 's/.#//' filename

Print file content in reverse order

# sed -n '1!G;h;#p' thegeekstuff.txt

Add line number for all non-empty-lines in a file

# sed '/./=' thegeekstuff.txt | sed 'N; s/\n/ /'

6. awk command examples

Remove duplicate lines using awk

# awk '!(#0 in array) { array[#0]; print }' temp

Print all lines from /etc/passwd that has the same uid and gid

#awk -F ':' '#3==#4' passwd.txt

Print only specific field from a file.

# awk '{print #2,#5;}' employee.txt

7. vim command examples

Go to the 143rd line of file

# vim +143 filename.txt

Go to the first match of the specified

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# vim +/search-term filename.txt

Open the file in read only mode.

# vim -R /etc/passwd

More vim examples: How To Record and Play in Vim Editor

8. diff command examples

Ignore white space while comparing.

# diff -w name_list.txt name_list_new.txt

2c2,3

< John Doe --- > John M Doe

> Jason Bourne

9. sort command examples

Sort a file in ascending order

# sort names.txt

Sort a file in descending order

# sort -r names.txt

Sort passwd file by 3rd field.

# sort -t: -k 3n /etc/passwd | more

10. export command examples

To view oracle related environment variables.

# export | grep ORACLE

declare -x ORACLE_BASE="/u01/app/oracle"

declare -x ORACLE_HOME="/u01/app/oracle/product/10.2.0"

declare -x ORACLE_SID="med"

declare -x ORACLE_TERM="xterm"

To export an environment variable:

# export ORACLE_HOME=/u01/app/oracle/product/10.2.0

11. xargs command examples

Copy all images to external hard-drive

# ls *.jpg | xargs -n1 -i cp {} /external-hard-drive/directory

Search all jpg images in the system and archive it.

# find / -name *.jpg -type f -print | xargs tar -cvzf images.tar.gz

Download all the URLs mentioned in the url-list.txt file

# cat url-list.txt | xargs wget –c

12. ls command examples

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Display filesize in human readable format (e.g. KB, MB etc.,)

# ls -lh

-rw-r----- 1 ramesh team-dev 8.9M Jun 12 15:27 arch-linux.txt.gz

Order Files Based on Last Modified Time (In Reverse Order) Using ls -ltr

# ls -ltr

Visual Classification of Files With Special Characters Using ls -F

# ls -F

More ls examples: Unix LS Command: 15 Practical Examples

13. pwd command

pwd is Print working directory. What else can be said about the good old pwd who has been printing the current directory name for ages.

14. cd command examples

Use “cd -” to toggle between the last two directories

Use “shopt -s cdspell” to automatically correct mistyped directory names on cd

More cd examples: 6 Awesome Linux cd command Hacks

15. gzip command examples

To create a *.gz compressed file:

# gzip test.txt

To uncompress a *.gz file:

# gzip -d test.txt.gz

Display compression ratio of the compressed file using gzip -l

# gzip -l *.gz

compressed uncompressed ratio uncompressed_name

2370997975 75.8% asp-patch-rpms.txt

16. bzip2 command examples

To create a *.bz2 compressed file:

# bzip2 test.txt

To uncompress a *.bz2 file:

bzip2 -d test.txt.bz2

More bzip2 examples: BZ is Eazy! bzip2, bzgrep, bzcmp, bzdiff, bzcat, bzless, bzmore examples

17. unzip command examples

To extract a *.zip compressed file:

# unzip test.zip

View the contents of *.zip file (Without unzipping it):

# unzip -l jasper.zip

Archive: jasper.zip

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LengthDate Time Name

-------- ---- ---- ----

40995 11-30-98 23:50 META-INF/MANIFEST.MF

32169 08-25-98 21:07 classes_

15964 08-25-98 21:07 classes_names

10542 08-25-98 21:07 classes_ncomp

18. shutdown command examples

Shutdown the system and turn the power off immediately.

# shutdown -h now

Shutdown the system after 10 minutes.

# shutdown -h +10

Reboot the system using shutdown command.

# shutdown -r now

Force the filesystem check during reboot.

# shutdown -Fr now

19. ftp command examples

Both ftp and secure ftp (sftp) has similar commands. To connect to a remote server and download multiple files, do the following.

# ftp IP/hostname

ftp> mget *.html

To view the file names located on the remote server before downloading, mls ftp command as shown below.

ftp> mls *.html -

/ftptest/features.html

/ftptest/index.html

/ftptest/othertools.html

/ftptest/samplereport.html

/ftptest/usage.html

20. crontab command examples

View crontab entry for a specific user

# crontab -u john -l

Schedule a cron job every 10 minutes.

*/10 * * * * /home/ramesh/check-disk-space

21. service command examples

Service command is used to run the system V init scripts. i.e Instead of calling the scripts located in the /etc/init.d/ directory with their full path, you can use the service command.

Check the status of a service:

# service ssh status

Check the status of all the services.

service --status-all

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Restart a service.

# service ssh restart

22. ps command examples

ps command is used to display information about the processes that are running in the system.

While there are lot of arguments that could be passed to a ps command, following are some of the common ones.

To view current running processes.

# ps -ef | more

To view current running processes in a tree structure. H option stands for process hierarchy.

# ps -efH | more

23. free command examples

This command is used to display the free, used, swap memory available in the system.

Typical free command output. The output is displayed in bytes.

# free

total used freeshared bufferscached

Mem: 3566408 1580220 19861880203988902960

-/+ buffers/cache:473272 3093136

Swap: 40001760 4000176

If you want to quickly check how many GB of RAM your system has use the -g option. -b option displays in bytes, -k in kilo bytes, -m in mega bytes.

# free -g

total used freeshared bufferscached

Mem: 311000

-/+ buffers/cache:02

Swap: 303

If you want to see a total memory ( including the swap), use the -t switch, which will display a total line as shown below.

ramesh@ramesh-laptop:~# free -t

total used freeshared bufferscached

Mem: 3566408 1592148 19742600204260912556

-/+ buffers/cache:475332 3091076

Swap: 40001760 4000176

Total:7566584 1592148 5974436

24. top command examples

top command displays the top processes in the system ( by default sorted by cpu usage ). To sort top output by any column, Press O (upper-case O) , which will display all the possible columns that you can sort by as shown below.

Current Sort Field: P for window 1:Def

Select sort field via field letter, type any other key to return

a: PID = Process Id v: nDRT = Dirty Pages count

d: UID = User Id y: WCHAN = Sleeping in Function

e: USER = User Namez: Flags = Task Flags

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........

To displays only the processes that belong to a particular user use -u option. The following will show only the top processes that belongs to oracle user.

# top -u oracle

25. df command examples

Displays the file system disk space usage. By default df -k displays output in bytes.

# df -k

Filesystem 1K-blocks Used Available Use% Mounted on

/dev/sda1 29530400 3233104 24797232 12% /

/dev/sda2 120367992 50171596 64082060 44% /home

df -h displays output in human readable form. i.e size will be displayed in GB’s.

ramesh@ramesh-laptop:~# df -h

Filesystem Size Used Avail Use% Mounted on

/dev/sda1 29G 3.1G 24G 12% /

/dev/sda2 115G 48G 62G 44% /home

Use -T option to display what type of file system.

ramesh@ramesh-laptop:~# df -T

Filesystem Type 1K-blocks Used Available Use% Mounted on

/dev/sda1ext4 29530400 3233120 24797216 12% /

/dev/sda2ext4 120367992 50171596 64082060 44% /home

26. kill command examples

Use kill command to terminate a process. First get the process id using ps -ef command, then use kill -9 to kill the running Linux process as shown below. You can also use killall, pkill, xkill to terminate a unix process.

# ps -ef | grep vim

ramesh 7243 7222 9 22:43 pts/2 00:00:00 vim

# kill -9 7243

27. rm command examples

Get confirmation before removing the file.

# rm -i filename.txt

It is very useful while giving shell metacharacters in the file name argument.

Print the filename and get confirmation before removing the file.

# rm -i file*

Following example recursively removes all files and directories under the example directory. This also removes the example directory itself.

# rm -r example

28. cp command examples

Copy file1 to file2 preserving the mode, ownership and timestamp.

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# cp -p file1 file2

Copy file1 to file2. if file2 exists prompt for confirmation before overwritting it.

# cp -i file1 file2

29. mv command examples

Rename file1 to file2. if file2 exists prompt for confirmation before overwritting it.

# mv -i file1 file2

Note: mv -f is just the opposite, which will overwrite file2 without prompting.

mv -v will print what is happening during file rename, which is useful while specifying shell metacharacters in the file name argument.

# mv -v file1 file2

30. cat command examples

You can view multiple files at the same time. Following example prints the content of file1 followed by file2 to stdout.

# cat file1 file2

While displaying the file, following cat -n command will prepend the line number to each line of the output.

# cat -n /etc/logrotate.conf

1/var/log/btmp {

2 missingok

3 monthly

4 create 0660 root utmp

5 rotate 1

6}

31. mount command examples

To mount a file system, you should first create a directory and mount it as shown below.

# mkdir /u01

# mount /dev/sdb1 /u01

You can also add this to the fstab for automatic mounting. i.e Anytime system is restarted, the filesystem will be mounted. /dev/sdb1 /u01 ext2 defaults 0 2

32. chmod command examples

chmod command is used to change the permissions for a file or directory.

Give full access to user and group (i.e read, write and execute ) on a specific file.

# chmod ug+rwx file.txt

Revoke all access for the group (i.e read, write and execute ) on a specific file.

# chmod g-rwx file.txt

Apply the file permissions recursively to all the files in the sub-directories.

# chmod -R ug+rwx file.txt

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More chmod examples: 7 Chmod Command Examples for Beginners

33. chown command examples

chown command is used to change the owner and group of a file. \

To change owner to oracle and group to db on a file. i.e Change both owner and group at the same time.

# chown oracle:dba dbora.sh

Use -R to change the ownership recursively.

# chown -R oracle:dba /home/oracle

34. passwd command examples

Change your password from command line using passwd. This will prompt for the old password followed by the new password.

# passwd

Super user can use passwd command to reset others password. This will not prompt for current password of the user.

# passwd USERNAME

Remove password for a specific user. Root user can disable password for a specific user. Once the password is disabled, the user can login without entering the password.

# passwd -d USERNAME

35. mkdir command examples

Following example creates a directory called temp under your home directory.

# mkdir ~/temp

Create nested directories using one mkdir command. If any of these directories exist already, it will not display any error. If any of these directories doesn’t exist, it will create them.

# mkdir -p dir1/dir2/dir3/dir4/

36. ifconfig command examples

Use ifconfig command to view or configure a network interface on the Linux system.

View all the interfaces along with status.

# ifconfig -a

Start or stop a specific interface using up and down command as shown below.

# ifconfig eth0 up

# ifconfig eth0 down

More ifconfig examples: Ifconfig: 7 Examples To Configure Network Interface

37. uname command examples

Uname command displays important information about the system such as — Kernel name, Host name, Kernel release number, Processor type, etc.,

Sample uname output from a Ubuntu laptop is shown below.

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# uname -a

Linux john-laptop 2.6.32-24-generic #41-Ubuntu SMP Thu Aug 19 01:12:52 UTC 2010 i686 GNU/Linux

38. whereis command examples

When you want to find out where a specific Unix command exists (for example, where does ls command exists?), you can execute the following command.

# whereis ls

ls: /bin/ls /usr/share/man/man1/ls.1.gz /usr/share/man/man1p/ls.1p.gz

When you want to search an executable from a path other than the whereis default path, you can use -B option and give path as argument to it. This searches for the executable lsmk in the /tmp directory, and displays it, if it is available.

# whereis -u -B /tmp -f lsmk

lsmk: /tmp/lsmk

39. whatis command examples

Whatis command displays a single line description about a command.

# whatis ls

ls(1) - list directory contents

# whatis ifconfig

ifconfig (8) - configure a network interface

40. locate command examples

Using locate command you can quickly search for the location of a specific file (or group of files). Locate command uses the database created by updatedb.

The example below shows all files in the system that contains the word crontab in it.

# locate crontab

/etc/anacrontab

/etc/crontab

/usr/bin/crontab

/usr/share/doc/cron/examples/crontab2english.pl.gz

/usr/share/man/man1/crontab.1.gz

/usr/share/man/man5/anacrontab.5.gz

/usr/share/man/man5/crontab.5.gz

/usr/share/vim/vim72/syntax/crontab.vim

41. man command examples

Display the man page of a specific command.

# man crontab

When a man page for a command is located under more than one section, you can view the man page for that command from a specific section as shown below.

# man SECTION-NUMBER commandname

Following 8 sections are available in the man page.

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1. General commands

System calls

C library functions

Special files (usually devices, those found in /dev) and drivers

File formats and conventions

Games and screensavers

Miscellaneous

2. System administration commands and daemons

For example, when you do whatis crontab, you’ll notice that crontab has two man pages (section 1 and section 5). To view section 5 of crontab man page, do the following.

# whatis crontab

crontab (1)- maintain crontab files for individual users (V3)

crontab (5)- tables for driving cron

# man 5 crontab

42. tail command examples

Print the last 10 lines of a file by default.

# tail filename.txt

Print N number of lines from the file named filename.txt

# tail -n N filename.txt

View the content of the file in real time using tail -f. This is useful to view the log files, that keeps growing. The command can be terminated using CTRL-C.

# tail -f log-file

More tail examples: 3 Methods To View tail -f output of Multiple Log Files in One Terminal

43. less command examples

less is very efficient while viewing huge log files, as it doesn’t need to load the full file while opening.

# less huge-log-file.log

One you open a file using less command, following two keys are very helpful. CTRL+F – forward one window

CTRL+B – backward one window

More less examples: Unix Less Command: 10 Tips for Effective Navigation

44. su command examples

Switch to a different user account using su command. Super user can switch to any other user without entering their password.

# su - USERNAME

Execute a single command from a different account name. In the following example, john can execute the ls command as raj username. Once the command is executed, it will come back to john’s account.

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[john@dev-server]# su - raj -c 'ls'

[john@dev-server]#

Login to a specified user account, and execute the specified shell instead of the default shell.

# su -s 'SHELLNAME' USERNAME

45. mysql command examples

mysql is probably the most widely used open source database on Linux. Even if you don’t run a mysql database on your server, you might end-up using the mysql command ( client ) to connect to a mysql database running on the remote server.

To connect to a remote mysql database. This will prompt for a password.

# mysql -u root -p -h 192.168.1.2

To connect to a local mysql database.

# mysql -u root -p

If you want to specify the mysql root password in the command line itself, enter it immediately after -p (without any space).

46. yum command examples

To install apache using yum.

# yum install httpd

To upgrade apache using yum.

# yum update httpd

To uninstall/remove apache using yum.

# yum remove httpd

47. rpm command examples

To install apache using rpm.

# rpm -ivh httpd-2.2.3-22.0.1.el5.i386.rpm

To upgrade apache using rpm.

# rpm -uvh httpd-2.2.3-22.0.1.el5.i386.rpm

To uninstall/remove apache using rpm.

# rpm -ev httpd

More rpm examples: RPM Command: 15 Examples to Install, Uninstall, Upgrade, Query RPM Packages

48. ping command examples

Ping a remote host by sending only 5 packets.

# ping -c 5 gmail.com

More ping examples: Ping Tutorial: 15 Effective Ping Command Examples

49. date command examples

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Set the system date:

# date -s "01/31/2010 23:59:53"

Once you’ve changed the system date, you should syncronize the hardware clock with the system date as shown below.

# hwclock –systohc

# hwclock --systohc –utc

50. wget command examples

The quick and effective method to download software, music, video from internet is using wget command.

# wget http://prdownloads.sourceforge.net/sourceforge/nagios/nagios-3.2.1.tar.gz

Download and store it with a different name.

# wget -O taglist.zip http://www.vim.org/scripts/download_script.php?src_id=7701

Copyright © 2008–2015 Ramesh Natarajan. All rights reserved | Terms of Service

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hash command line for Linux. alias Create an alias •

apropos Search Help manual pages (man -k)

apt-get Search for and install software packages (Debian/Ubuntu)

aptitude Search for and install software packages (Debian/Ubuntu)

aspell Spell Checker

awk Find and Replace text, database sort/validate/index

b

basename Strip directory and suffix from filenames

bashGNU Bourne-Again SHell

bc Arbitrary precision calculator language

bg Send to background

break Exit from a loop •

builtin Run a shell builtin

bzip2 Compress or decompress named file(s)

c

cal Display a calendar

caseConditionally perform a command

cat Concatenate and print (display) the content of files

cd Change Directory

cfdisk Partition table manipulator for Linux

chgrp Change group ownership

chmod Change access permissions

chown Change file owner and group

chroot Run a command with a different root directory

chkconfig System services (runlevel)

cksum Print CRC checksum and byte counts

clear Clear terminal screen

cmp Compare two files

commCompare two sorted files line by line

command Run a command - ignoring shell functions •

continue Resume the next iteration of a loop •

cp Copy one or more files to another location

cronDaemon to execute scheduled commands

crontab Schedule a command to run at a later time

csplit Split a file into context-determined pieces

cut Divide a file into several parts

d

dateDisplay or change the date & time

dc Desk Calculator

dd Convert and copy a file, write disk headers, boot records

ddrescue Data recovery tool

declare Declare variables and give them attributes •

df Display free disk space

diffDisplay the differences between two files

diff3 Show differences among three files

dig DNS lookup

dir Briefly list directory contents

dircolors Colour setup for `ls'

dirname Convert a full pathname to just a path

dirsDisplay list of remembered directories

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dmesg Print kernel & driver messages

du Estimate file space usage

e

echoDisplay message on screen •

egrep Search file(s) for lines that match an extended expression

eject Eject removable media

enable Enable and disable builtin shell commands •

env Environment variables

ethtool Ethernet card settings

evalEvaluate several commands/arguments

execExecute a command

exitExit the shell

expect Automate arbitrary applications accessed over a terminal

expand Convert tabs to spaces

export Set an environment variable

exprEvaluate expressions

f

false Do nothing, unsuccessfully

fdformat Low-level format a floppy disk

fdisk Partition table manipulator for Linux

fg Send job to foreground

fgrep Search file(s) for lines that match a fixed string

fileDetermine file type

findSearch for files that meet a desired criteria

fmt Reformat paragraph text

foldWrap text to fit a specified width.

for Expand words, and execute commands

format Format disks or tapes

freeDisplay memory usage

fsckFile system consistency check and repair

ftp File Transfer Protocol

function Define Function Macros

fuser Identify/kill the process that is accessing a file

g

gawkFind and Replace text within file(s)

getopts Parse positional parameters

grepSearch file(s) for lines that match a given pattern

groupadd Add a user security group

groupdel Delete a group

groupmod Modify a group

groups Print group names a user is in

gzipCompress or decompress named file(s)

h

hashRemember the full pathname of a name argument

headOutput the first part of file(s)

helpDisplay help for a built-in command •

history Command History

hostname Print or set system name

htopInteractive process viewer

i

iconv Convert the character set of a file

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id Print user and group id's

if Conditionally perform a command

ifconfig Configure a network interface

ifdown Stop a network interface

ifupStart a network interface up

import Capture an X server screen and save the image to file

install Copy files and set attributes

ip Routing, devices and tunnels

j

jobsList active jobs •

joinJoin lines on a common field

k

killKill a process by specifying its PID

killall Kill processes by name

l

lessDisplay output one screen at a time

let Perform arithmetic on shell variables •

linkCreate a link to a file

ln Create a symbolic link to a file

local Create variables •

locate Find files

logname Print current login name

logout Exit a login shell •

lookDisplay lines beginning with a given string

lpc Line printer control program

lpr Off line print

lprint Print a file

lprintd Abort a print job

lprintq List the print queue

lprmRemove jobs from the print queue

ls List information about file(s)

lsofList open files

m

makeRecompile a group of programs

man Help manual

mkdir Create new folder(s)

mkfifo Make FIFOs (named pipes)

mkisofs Create an hybrid ISO9660/JOLIET/HFS filesystem

mknod Make block or character special files

moreDisplay output one screen at a time

mostBrowse or page through a text file

mount Mount a file system

mtools Manipulate MS-DOS files

mtr Network diagnostics (traceroute/ping)

mv Move or rename files or directories

mmv Mass Move and rename (files)

n

netstat Networking information

niceSet the priority of a command or job

nl Number lines and write files

nohup Run a command immune to hangups

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notify-send Send desktop notifications

nslookup Query Internet name servers interactively

o

openOpen a file in its default application

op Operator access

p

passwd Modify a user password

paste Merge lines of files

pathchk Check file name portability

pingTest a network connection

pkill Kill processes by a full or partial name.

popdRestore the previous value of the current directory

pr Prepare files for printing

printcap Printer capability database

printenv Print environment variables

printf Format and print data •

ps Process status

pushd Save and then change the current directory

pv Monitor the progress of data through a pipe

pwd Print Working Directory

q

quota Display disk usage and limits

quotacheck Scan a file system for disk usage

quotactl Set disk quotas

r

ram ram disk device

rar Archive files with compression

rcp Copy files between two machines

readRead a line from standard input •

readarray Read from stdin into an array variable •

readonly Mark variables/functions as readonly

reboot Reboot the system

rename Rename files

renice Alter priority of running processes

remsync Synchronize remote files via email

return Exit a shell function

rev Reverse lines of a file

rm Remove files

rmdir Remove folder(s)

rsync Remote file copy (Synchronize file trees)

s

screen Multiplex terminal, run remote shells via ssh

scp Secure copy (remote file copy)

sdiff Merge two files interactively

sed Stream Editor

select Accept keyboard input

seq Print numeric sequences

set Manipulate shell variables and functions

sftpSecure File Transfer Program

shift Shift positional parameters

shopt Shell Options

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shutdown Shutdown or restart linux

sleep Delay for a specified time

slocate Find files

sortSort text files

source Run commands from a file '.'

split Split a file into fixed-size pieces

ssh Secure Shell client (remote login program)

statDisplay file or file system status

strace Trace system calls and signals

su Substitute user identity

sudoExecute a command as another user

sum Print a checksum for a file

suspend Suspend execution of this shell •

syncSynchronize data on disk with memory

t

tailOutput the last part of file

tar Store, list or extract files in an archive

tee Redirect output to multiple files

testEvaluate a conditional expression

timeMeasure Program running time

timeout Run a command with a time limit

times User and system times

touch Change file timestamps

top List processes running on the system

tputSet terminal-dependent capabilities, color, position

traceroute Trace Route to Host

trapRun a command when a signal is set(bourne)

tr Translate, squeeze, and/or delete characters

trueDo nothing, successfully

tsort Topological sort

tty Print filename of terminal on stdin

typeDescribe a command •

u

ulimit Limit user resources •

umask Users file creation mask

umount Unmount a device

unalias Remove an alias •

uname Print system information

unexpand Convert spaces to tabs

uniqUniquify files

units Convert units from one scale to another

unrar Extract files from a rar archive

unset Remove variable or function names

unshar Unpack shell archive scripts

until Execute commands (until error)

uptime Show uptime

useradd Create new user account

userdel Delete a user account

usermod Modify user account

users List users currently logged in

uuencode Encode a binary file

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uudecode Decode a file created by uuencode

v

v Verbosely list directory contents (`ls -l -b')

vdirVerbosely list directory contents (`ls -l -b')

vi Text Editor

vmstat Report virtual memory statistics

w

waitWait for a process to complete •

watch Execute/display a program periodically

wc Print byte, word, and line counts

whereis Search the user's #path, man pages and source files for a program

which Search the user's #path for a program file

while Execute commands

who Print all usernames currently logged in

whoami Print the current user id and name (`id -un')

wgetRetrieve web pages or files via HTTP, HTTPS or FTP

write Send a message to another user

x

xargs Execute utility, passing constructed argument list(s)

xdg-open Open a file or URL in the user's preferred application.

yes Print a string until interrupted

zip Package and compress (archive) files.

. Run a command script in the current shell

!! Run the last command again

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