Linux is an open-source operating system which is the first choice of every technocrat. For VLSI Design Engineers also most of the EDA tools are only compatible with Linux. In Linux, we interact with OS majorly with Command-Line Interface (CLI). In beginning, it might look a bit tedious as you have to remember lots of commands and we are addicted to GUI interface but later you will definitely love it.
In this article, we will learn some of basic Linux commands with examples. I would request to my reader don't just read this article but, practice these commands parallelly for best understanding and clarity. If you wish you can also make a small cheat sheet for your use. In this article, we will learn 4 categories of 50 most useful basic commands. For advance level commands we are going to publish another article later.
Category-1: File System Management
1. ls
: list files and directories
ls -l ; indicates file/directory type, permissions, owner, size, last modified
- normal, d- directory, s-socket file, l-link file
ls -a ; shows hidden files/directories
ls -t ; lists the files/directory on basis of modification time
ls -lart ; lists all the files and directories in order of last modified.
2. clear
: clear the terminal (but keep the history of commands intact)
3. man / --help
: Show a manual of command and switches written in details.
4. pwd
: Print Working Directory, The directory where you are currently.
5. cd
: Change Directory, to move to another directory.
Use:
cd .. ; back to parent directory
cd - ; back to previous directory
cd ~ ; go to home directory
cd ../../../ ; back to n steps
cd ‘abc xyz’ ; go to a directory whose name contain white space
6. mkdir
: create a directory
Use:
mkdir directory_name ; To create a new directory with the given name.
mkdir dir1 dir2 dir3 ; To create multiple directories in a single step.
7. touch
: create a file
Use:
touch file_name ; create a new file
touch file1 file2 file3 ; To create multiple files
touch –a file_name ; to change file access time
touch –m file_name ; to change the file modification time
8. gedit file_name &
: create and edit a file in GUI mode
Use:
gedit /path/to/file_name ; create and edit a file in specified location
; word count, line no. , language
9. vi file_name
: create and edit a file using command-line interface
Use:
i ; Switch to edit mode
ESc ; Exit from edit mode and Switch to command mode
/string ; find the string
Esc + :q ;exit without saving
Esc + :s ; Save only not exit
Esc + :wq ; save and exit
10. cp source destination
: copy command
Use:
cp source_file destination_dir ; To copy a file
cp source_file . ; To copy a file to current directory ("." means current dir)
cp -f source_file destination_dir ; To copy forcefully a regular file
cp -R source_file destination_dir ; To coppy recursive a directory
11. mv source destination
: move command, like cut+paste
Use:
mv f1 f2 ; rename f1 by f2
mv -rf ; recursive and force moving of a directory
12. rm
: remove file/directory, like delete
Use:
rm -rf ; remove recursive and force
! One of dangerous command as root, use carefully!!!
rm *.txt ; Will remove all the file having extension .txt in PWD
13. cat
: stands for concatenate
Use:
cat file_name ; Display a contain of a file in CLI
cat text1 > text2 ; redirection of text, overwrite
cat text1 >> text2 ; appending the text
14. which
: Path of the command
Use:
which virtuoso ; Display the path of the executable file for virtuoso
which vi ; Will show the vi command path
which python ; Will show the installation path of the python program
15. find
: searching a file/directory
Use:
find / -name "dir_name" ; to find a file/dir
find /home/user_name -name "file_name" ; to find a file/dir only in user's home area
man find ; to get more details on find command
16. history
: Get the list of executed commands
Use:
history ; the history of all command
history n ;list of last n command executed
!n ; repeat any command in the history list
export HISTTIMEFORMAT=‘%F %T ’ ; setting history command with timestamp format
unset export HISTTIMEFORMAT ; unsetting the time format
history -c ; clear all the history
~/.bash_history ; location of stored command history
17. chmod
: Change mode, change the permission of file/directory
Use:
ls -l file_name ; To see the current permissions of the file/dir
Let's understand the permissions through this ecample.
r w x 7 7 7 7 5 4
4 2 1 rwx rwx rwx rwx r-x r- -
Numeric and Symbolic permissions
chmod 777 file_name ; set all the permission for all users
chmod 754 file_name ; set rwx for owner, r-x for the group and r– for others
chmod –R 777 dir_name ; Set all permission recursively inside the dir
Category-2: Text processing commands
18. touch
: create a new file
Use:
touch file1 ; create an empty file
touch file1 file2 file3 ; create multiple files in one command
touch –am file2 ; change access and modification time
19. gedit
: A GUI based Linux text editor
Use:
gedit & ; open gedit text editor and release the CLI
gedit file1 ; create/open a file in geditor
20. head
: To read the first 10 lines of a file in CLI
Use:
head file_name ; To read the first 10 lines of a file
head –n 8 file_name ; To read first 8 lines of a file OR head -8 file
head -4 *.log ; Read first 4 lines of all log files in PWD
21. tail
: To read the last 10 lines in the command line
Use:
tail file_name ; To read last 10 lines of a file
tail –n 12 file_name ; To read last 12 lines of a file OR tail -2 file
22. sort
: To sort the list
Use:
sort file_name ; sort the content of file
sort –n file_name ; sorting a file which has numbers
sort –r file_name ; sorting the file in reverse order
sort –o outputfile inputfile ; redirection of sorted output
sort –n -k2 file_name ; sorting the file on basis of the nth column
23. unique
: An utility for filtering the repeated lines in a file
Use:
unique file_name ; will display only unique lines
unique –c file_name ; will tell no. of times a line has repeated
24. more
: Display text one screen at a time
Use:
more file_name ; display the text in command line
<space> next screen,
<b> back to previous screen,
<enter> next line
more -10 file_name ; will display 10 lines at a time
dmesg | more ; more with pipe.
25. less
: to read the text file in the command line
Use:
less file_name ; To view the content of a file
similar to more command with some advance features
less -N file_name ; Will show the content with line number
<Enter> or Down Arrow: To move next line
Up Arrow: to move up a line
<space>: To move down one page
<b>: To move up one page
26. grep
: global regular expression print
Use:
grep –i words file_name ; display the line contains searched word
dmesg | grep sda ; filtered the output and show only line having sda
dmesg | grep sda –A 5 ; Display 5 lines after the matching word sda
27. diff or vimdiff
: find the difference between two files/dir
Use:
diff file1 file2 ; To check the difference between two files
diff dir1 dir2 ; To check the difference between contains of two dir
A similar GUI tool is “meld”
vimdiff f1 f2 , gvimdiff f1 f2
28. wc
: word count of a file
Use:
wc file_name ; Newline, word and byte count in the file
wc –l file_name ; To count total new lines in the file
wc –w file_name ; T count total words only
wc –c file_name ; T count total characters only
Category-3: Process management commands
29. top or htop
: It will show the status of various resources and tasks
Use:
top ; you can see the utilization statics for resources and get PID of all running process
htop ; Similar to the top command but an improved version.
30. ps
: Known as Process Status
Use:
ps ; process for the current shell
ps -e ; Display all active process
ps -ef ; Display all active process in full format
ps –ef | grep virtuoso ; If the list is too big we can grep it to a specific command
31. kill
: To terminate a process
Use:
kill PID ; Killing a process by PID, PID is a numeric value.
kill PID1 PID2 PID3 ; Kill multiple processes together. You can specify the signal name in between Kill and PID. If no signal has been specified, by default TERM signal will be sent.
32. who
: Display the users who are currently logged in your Linux machine
Use:
who ; Without any argument who command will display user's login name, terminal, login time and host
who –q ;Display the name of all users and total no. of users logged in
33. w
: information about current logged user and what they are doing
34. users
: Display the all current users name in a single line
35. last
: it display the list of user who logged the system
Use:
last ; If no options provided the last command displays a list of all users logged in (and out) since /var/log/wtmp file was created
last user_name ;Will display the activities of a particular user only
36. free
: Used to check available physical memory and swap memory
Use:
free ; Command used to check used and free memory space in KB
free –m/g ;Space will be shown in MB or GB
free -s 5 ; Will update the status in every 5 seconds.
37. lshw
: Used to check hardware information
Use:
lshw ; Generates detail reports about various hardware of system
lshw –class memory ;Details memory in the system
lshw –class processor ; Details of processor in the system
lshw –short –class disk ; Details about the hard drives (network)
38. lscpu
: Display information about CPU architecture
Use:
lscpu ; Give the detailed information about the CPU
39. cat /proc/cpuinfo
: Similar information like lscpu
40. dmidecode
: Is a tool for dumping System Management BIOS (SMBIOS) table content in a human-readable format
Use:
dmidecode ; Gives all the hardware details
dmidecode –t system ; Gives the manufacturer, model no. etc details
dmidecode –t bios ; Gives the bios information of system (/memory)
41. uptime
: Gives the time how long system is running
Use:
uptime -p ; Gives the duration of the system running
42. reboot
: Will shutdown and restart the machine instantly
43. shutdown
: Can be used to shut down or restart the machine
Use:
shutdown –h now ; System will be shut down instantly
shutdown –h +5 “message” ; System will be shut down after 5 minute
shutdown –r +5 ; System will be restart after 5 minutes
Category-4: Bash Environment Related Commands
44. date
: Will show the current date, time and of time zone
Use:
date ; Will show day, date, current time and timezone
date –d “1990-12-31” ; Details of any specific date
timedatectl ; Will show details of local and universal time and timezone
timedatectl set-time ‘2018-12-27 07:30:10’ ; to set specific date and time
timedatectl set-time ‘Asia/Kolkata’ ; Setting time by time zone
45. cal
: Will display the calendar of current month in terminal
Use:
cal ; Will show calendar of current month in terminal
cal 08 1947 ; To display a calendar of particular month and year
cal –y 2019 ; Will show calendar of all month of a particular year
46. env
: Used to print all the current environment variables and it’s value
47. whoami
: prints the username of the current user
48. uname
: It provides kernel versions and other details
Use:
uname ; Without any option, will print kernel name only
uname -a ; Get all the information like, kernel name, version, architecture, host name, current date and time.
49. hostname
: To know the hostname
hostname ;It will display the hostname
cat /etc/hostname ;Inside the hostname file hostname is stored and we can read and edit.
vi /etc/hostname ;to change a new hostname edit the name here and reboot the machine
50. echo $BASH_VERSION
: To know the BASH version. For more variables value run env command
