To show the full path of shell commands found in your path
which <command name>
eg: which grep
//output like: /bin/grep
To locate the program, source code, and manual page for a command
whereis <command name>
To search for files anywhere on the file system
locate <keyword to search>
//find all files and directories that contain the keyword
To search for files matching certain patterns
find <directory name> <pattern to search>
eg: find . -name \*mp3
//starts searching in the current directory “.” and all
subdirectories, looking for files with “mp3” at the end of their
names
To list currently running process
ps
To list all process in the system
ps -aux
To show who is logged on and what they are doing
w
who
To view the name of current user
whoami
To view the user details
finger
To view host name
hostname
To set host name
hostname -a <new host name>
To print your user-id and group id's
id
To get report on file system disk space usage
df
In MB
df -h
To view disk usage in a particular directory
du
To view summary
du -s
In MB
du -h
To display CPU processes in a full-screen GUI
top
// type “Q” to quit
To display amount of free and used memory in the system
free
To display information about your CPU
cat /proc/cpuinfo
To display lots of information about current memory usage
cat /proc/meminfo
To print system information to the screen
uname -a
To print kernel version
uname -r
To display the size of a file
wc -l
In bytes
wc -m
In char
wc -c
In word count
wc -w
To change permission to a file/directory
chmod [-R] <permissions> <file name/directory name>
eg: chmod 754 one.txt
eg: chmod -R 777 /home/songs/
{
read r=4; write w=2; execute x=1
Owner Group Others
rwx r-x r--
7 5 4
}
To change ownership of a file/directory
chown [-R] <user name> <file name/directory name>
eg: chown dhanoop one.txt
eg: chown -R dhanoop /home/songs/
To search a file for a particular pattern
grep [-R] <word to search> <file name/directory name>
eg: grep science science.txt
//case-sensitive search
eg: grep -i science science.txt
//case-insensitive search
eg: grep -i ‘spinning top’ science.txt
//multiword search
eg: grep -R passwd /etc/
//search in directory
To clear the screen
clear
To display text on screen
echo “<text to display>”
eg: echo “Hello”
To print a file or program output
lpr <file name>
eg: lpr mp3files.txt
<command> | lpr
eg: ls -la | lpr
To sort a file or program output
sort
eg: sort mp3files.txt
To switch user
su <user name>
//to switch to a particular user account
su
//to switch to root account
su -
//to switch to root, and log in with root's environment
To give an alias name to a command for ease of use
alias <name>=”<command>”
eg: alias list=”ls -l”
To display last logins of user
last
To display the name of currently working terminal
tty
To block a user
passwd -l <user name>
To unblock a user
passwd -u <user name>
To add a user account
useradd [options] <username>
With specified home directory
useradd -d <home directory> <user name>
With specified shell
useradd -s <shell> <user name>
With specified initial group
useradd -g <initial group> <user name>
With specified expiry date
useradd -e <YYYY-MM-DD> <user name>
To lock/unlock a user account
usermod [-L or -U] <user name>
To delete a user account
userdel [-r] <user name>
To restart the system
shutdown -r now
//without delay
To turn off the system
poweroff
To reboot the system
reboot
To halt the system
halt
To mount a file system or media
mount <source> <destination>
eg: mount /dev/sda1 /mnt
//mounting first partition of first SATA hard disk
eg: mount /dev/hdb3 /mnt
//mounting third partition of second hard disk
To umount a file system or media
umount <file system/media>
eg: umount /mnt
To view IP address
ifconfig
To edit IP address temporarily
ifconfig -a etho <ipaddress>
To view partitions and file systems
fdisk -l
//view line by line
To print selected columns in a file
cut -c <column range> <file name>
eg: cut -c 3-5 sem.txt
To print particular fields
awk ‘{ print $<field number> }’ <file name>
eg: awk ‘{ print $2 }’ sem.txt
//prints second field
eg: awk ‘{ print $1 $3 }’ sem.txt
//prints first and third fields
To know the shell
echo $SHELL
//the symbol “$” precedes every user or system variable.
All system variables are BLOCK lettered.
To know the home directory
echo $HOME
To print the calendar
cal
//prints calendar of current month
cal <YYYY>
eg: cal 2010
//prints calendar of specified year
To print the date
date
To temporarily switch to root to execute a single command
sudo <command>
eg: sudo ifconfig -a eth0 192.168.1.101
To run an executable file
sh <file name>
eg: sh new\ file
//”\ “ denotes white space
./<file name>
eg: ./new\ file
To view command history
history
To re execute last command
!!
To execute nth command in history
!n
eg: !444
//executes 44th command in the history
To re execute last command that starts with specified character
!<char>
eg: !s
//executes the last command that starts with letter “s”
To repeat the last command changing old character to new character
^old^new
eg: ^l^m
//let “wc -l” be the last command
now “wc -m” will be executed
Signals to a process
To list all signals
kill -l
To kill a process
kill <process id>
To terminate a process
kill -9 <process id>
To normally exit a process
kill -15 <process id>
To login remotely to a system
ssh [<user name>@]<ip address>
eg: ssh dhanoopbhaskar@192.168.1.101
To execute a command on remote system through remote login
ssh [<user name>@]<ip address> <command>
eg: ssh dhanoopbhaskar@192.168.1.101 df -h
//executing “df -h” remotely
To copy file from a remote system
scp [-r] <source> <destination>
eg: scp /home/a.c dhanoopbhaskar@192.168.1.101:/home/
0 Comments