Linux Commands - Quick Reference
Change Directory/List directories
Change directorycd ~(home directory)
/(root directory)
List files/directories
ls -l (long format)
-a (hidden files) S(Sort by size)
-R (List sub-directories recursively)
Create/copy/move File
Finds the type of the file. useful when the type of file is unknown.file <file name>
Make directory
mkdir -p <Dir./Sub Dir.> (create parent dirs if not present)
-m mode or permissions to the directory
eg: mkdir -m 777 newdir
Remove directory(ies)
rmdir -p <Dir./Sub Dir.> (remove the whole directory structure)
-v (verbose)
Remove file(s)
rm -r (Remove directories and their contents)
-v (verbose)
-i (interactive)
Copy/Move files
cp (or) mv -i (interactive)
-R (Recursive copying)
-v (verbose)
cp <options> <sources seperated by space> <destination>
Secure copy
scp -r recursive copy
-P port
-i location of the public key file {for establishing connection with private public key}
scp <file name1> <file name2> <host name@IP address:dest folder>
eg: scp test.txt localhost@10.0.2.15:/home/naresh [local to remote copy]
scp localhost@10.0.2.15:/home/naresh/test.txt /home/ [Remote to local copy]
Symbolic links
ln -s symbolic link
ln <options> <target> <link name>
eg: ln -s /home/test.sh test
Change permissions of a file
chmod -rw-rw-r--x [<user in rwx> <group in rwx> <others in rwx>] where r is read, w is write, x is execute
eg: chmod 0+wx file.txt (adds wx to other users)
chmod g-w file.txt (Removes write permission for group)
chmod ug=rwx (assigns rwx to both owner and group)
chmod a-w (removes write permission for all the users)
chmod +x (adds execute permission for all the users)
eg in Octal representation:
r w x in binary is 4 2 1 equivalent to 4+2+1=7
r - x in binary is 4 0 1 equivalent to 4+0+1=5
r - - in binary is 4 0 0 equivalent to 4
Reading file contents
Concatenate files and print on the standard o/pcat -b add line nos to nonblank lines
-n add line nos
-s squeeze blank lines
-E displays $ at the end of the line
cat <file name1> <file name2> ; [ctrl+d for exit]
File Traversal less
less <space> page by page
<b> backwards page by page
<G> EOF
<g> Top of the file
</<search text>> search text from top to bottom in the file (n for next, N for previous)
<?><search text>> search text from bottom to top in the file
Log file/continous file traversal
head,tail -n <no of line> no. of lines to show
-f follow
+n start from line 'n' [used with tail]
head <options> <file name> <file name>
head: First part of the file -10 lines , tail: Last part of the file -10 lines
Word count
wc -l no. of lines
-c no. of chars
-w no. of words
-L length of the longest line
wc <file name>
Eg: wc test.java
Output : 9 13 110 Test.java
Here 9 is no. of lines, 13 is no. of words, 110 is no. of chars
List/Find Processes
Display Linux processestop -s <no.> no. of seconds to refresh
-i toggles idle process
-k process to kill
-q exit
Reports a snapshot of current processes
ps -a all process irrespective of the user
-x all running processes
-u <user name> filters processes by user
-w shows full command name of the processes
-C <process name> filters process by process name
Finding the processid
pidof <process name>
Sending singnal to a process
kill -STOP {freezes the process}
-CONT {Resumes the stopped process}
kill <flags> <pid>
Execute a process(script/command) periodically
watch -n <no.> interval in seconds
watch <command>
Command help/Locate command
Locate a commandwhich <command name>
eg: which bash
output : /bin/bash
Short desciption of the command
whatis <command>
Command manual
man -k search by keyword
man <options> <command name>
Add (or) Remove user/Add (or) Remove group/Adding users to group
Create a new user or updated default new user informationuseradd -m creates home directory for the user
-s default shell; allows the user to use shell
-g group name
-c comments
useradd <user name> <options>
Deletes a user account and related files
userdel -r removes user directory also
userdel <username>
Create a group
groupadd <group name>
Delete a group
groupdel <group name>
Linking user to a group
gpasswd -a adding the user to the group
-d removing the user from the group
gpasswd <options> <user name> <group name>
Find Memory Available/Memory used
Disk space availabledf -h human readable form
Disk space used
du -h human readable form
-s summaryDisplay the total amount of free and used memory in the system
free -h human readable form
-m megabyte format
Search Files/Search text
File Searchfind -name name of the file
-mtime <no.> files which are created 'n' days ago
-P Never follow periodic link
-empty shows empty files
-type type of the file, file or directory
-delete delete the files that are found
find <directory> -name <file name>
Text Search
grep -i case insensitive
-n prints the line number
-v invert match (works opposite to match)
grep <options> <"search key"> <file name1> <file name2> ..
Translate or delete characters
tr -d delete chars
-c complement
-s squeeze
tr <options> <SET1> <SET2>
Translates set1 of characters to set2 of characters
eg: echo hello world | tr a-z A-z
HELLO WORLD
echo hello world | tr '[:lower]' '[:upper]'
HELLO WORLD
echo hello world | tr '[:space]' \t
HELLO WORLD
echo hello world | tr -d 'h'
ello world
echo "my username is 432234" | tr -cd [:digit:]
432234 [delete all the characters except numbers]
Network details
Configure a network interfaceifconfig down {turns off the internet connection}
up {connects to the internet connection}
ifconfig <name of new interface> <options>
Print n/w connections, routing tables, interface statistics,etc.,
netstat -a all
-t shows tcp conections
-u shows udp connections
-l listening state connections
-s statistics
-p pid of the listed conections
-n ports of the listed connections
-c continous status / refreshes the screen periodically
-ie same as ifconfig
Utilities
TAR archiving utilitytar -c creating an archive
-x extracting an archive
-v verbose
-f Allows to specify a file name
-z used for gzip format
tar <options> <tar file name in .tar> <folder to archive>
eg: tar -cvf for creating
tar -xvf for extracting
tar -czvf for creating {Order of options matter}
gz
unzip
APT package handling utility
apt-get install {installs the software}
remove {removes the software from the system}
remove --purge {removes the software as well as configuration files related to the s/w}
autoremove {removes the supporting software }
update {updates the software}
sudo apt-get install <software name>Display/echoes the command arguments
echo -e Removes escape characters while echoing
update the time stamp of a given file or create an empty file
touch <file>
Rich text editor
nano <file>
Notepad type of editor in linux
gedit <file>
Date/Calendar
cal <year> shows the calendar of all the months<month> <year> shows the calendar for a month in the year
date -s set the date
date +%d-%h-%y - shows date in dd-MMM-yy format
mailx
mutt
Shell utilities
cat > log.txt - Fills the result of a command to txt>> log.txt - Appends the content to the log.txt
wildcards - */ - for directories /*.* - every file /*.log - only files with log extension
Executes multiple commands sequentially
ls; echo hello
Executes multiple commands sequentially; When the previous command fails, the next command won't be executed and outputs nothing
lS && echo hello
Executes multiple commands sequentially; If the first command is successful, next command won't be run and outputs first command (works like a or statement in any programming language)
ls || echo hello
Outputting previous command's output to net
ls | grep 'Music'
Outputs the ls command output to grep, so that grep can use that output for searching
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