Linux Basic Commands

 

Linux Basic Commands

 

File Commands

Is - directory listing
Is -al - formatted listing with hidden files
cd dir - change directory to dir
cd - change to home
pwd - show current directory
mkdir dir - create a directory dir
rm file - delete file
rm -r dir - delete directory dir
rm -f file - force remove file
rm -rf dir - force remove directory dir *
cp filel file2 - copy filel to file2
cp -r dirl dir2 - copy dirl to dir2; create dir2 if it doesn't exist  mv fiLe1 fiLe2 - rename or move file1 to file2  if file2 is an existing directory, moves filel into directory file2
mv <file name> Rename the file with new name

In -s file Link - create symbolic link link to file
touch file - create or update file
cat file - places standard input into file
more file - output the contents of file
head file - output the first 10 lines of file
tail file - output the last 10 lines of file
tail -f file - output the contents of file as it  grows, starting with the last 10 lines

 

Process Management

 

ps - display your currently active processes

ps aux – ps with lot of detail

top - display all running processes

kill pid - kill process id pid

killall proc - kill all processes named proc *

bg - lists stopped or background jobs; resume a stopped job in the background

fg - brings the most recent job to foreground

fg n - brings job n to the foreground File Permissions

chmod octal file - change the permissions of file to octal, which can be found separately for user, group, and world by adding:

e 4 - read (r)
e 2 - write (w)
e 1 - execute (x)

Examples:
chmod 777 - read, write, execute for all
chmod 755 - rwx for owner, rx for group and world
For more options, see man chmod.

SSH
ssh user@host - connect to host as user
ssh -p port user@host - connect to host on port as user

ssh -D port user@host – connect and use bind port
ssh-copy-id user@host - add your key to host for user to enable a keyed or passwordless login

Searching

 

grep pattern files - search for pattern in files

grep -r pattern dir - search recursively for pattern in dir command I grep pattern - search for pattern in the output of command

locate file - find all instances of file

 

System Info 

date - show the current date and time 

cal - show this month's calendar 
uptime - show current uptime 
w - display who is online 
whoami - who you are logged in as 
finger user - display information about user 
uname -a - show kernel information 
cat /proc/cpuinfo - cpu information 
cat /proc/meminfo - memory information 
man command - show the manual for command 
df - show disk usage 
du - show directory space usage 
free - show memory and swap usage 
whereis app - show possible locations of app 

which app - show which app will be run by default 

Compression 

tar cf file. tar files - create a tar named file.tar containing files 
tar xf file. tar - extract the files from file.tar 
tar czf file. tar.gz files - create a tar with 

tar xjf file. tar.bz2 - extract a tar using Bzip2 
tar xzf file. tar.gz - extract a tar using Gzip 

Tar flags

c - create archive

t – table of contents

x – extract 

f – specific filename 

z – use zip/gzip

j – bzip2 compression

k – do not overwrite 

T – files from file

w – ask for confirmation

v – verbose 

Gzip compression  

gzip file - compresses file and renames it to file.gz 

gzip -d file.gz - decompresses file.gz back to file 

Network 

ping host - ping host and output results 
whois domain - get whois information for domain 
dig domain - get DNS information for domain 
dig -x host - reverse lookup host 
wget file - download file 
wget -c file - continue a stopped download 

wget –r url – recursively download files from url 

User Management Command

 

>> adding new user:

#useradd rohan – add user named “rohan”

#who - Show who is logged into the system.

#groupadd IT - Create a group named "IT".

#userdel rohan – delete user named “rohan” 

#usermod –ag IT rohan – add Rohan account to IT Group.

#passwd –l rohan – change password of Rohan account. 

 

Shortcuts 

Ctrl+C - halts the current command 

Ctrl+Z - stops the current command, resume with  fg in the foreground or bg in the background 

Ctrl+D - log out of current session, similar to exit 

Ctrl+W - erases one word in the current line 

Ctrl+U - erases the whole line 

Ctrl+R - type to bring up a recent command 

exit - log out of current session