120+ Linux Commands That Are Actually Useful




The Linux kernel, created by Linus Torvalds, was made available to the world for free. Torvalds then invited others to add to the kernel provided that they keep their contributions free. Thousands of programmers began working to enhance Linux, and the operating system grew rapidly. Because it is free, open-source and runs on PC platforms, it gained a great audience among developers very quickly. However, Linux is harder to manage than something like Windows, but offers more flexibility and configuration options. 



In this post, I am going to give you a list of useful and commonly used linux commands. I divide these commands into 10 different categories and give a description for all of them. Also, the pdf cheat-sheet of all these commands is available for download at the bottom. 

Alright, let's start:

1. SYSTEM





$ uname -a Displays Linux system information

$ uname -r Displays kernel release information

$ uptime Shows how long system running + load

$ hostname Shows system host name

$ hostname -i  Displays the IP address of the host

$ last reboot Shows system reboot history

$ date Shows the current date and time

$ cal Shows this month calendar

$ whoami Shows who you are logged in as


2. HARDWARE


$ dmesg Detected hardware and boot messages

$ cat /proc/meminfo Hardware memory information

$ cat /proc/cpuinfo CPU model information

$ cat /proc/interrupts Lists the number of interrupts per CPU per I/O device

$ sudo lshw Displays information on hardware configuration of the system

$ lsblk Displays block device related information in Linux (sudo yum install util-linux-ng)

$ free -m Displays used and free memory (-m for MB)

$ lsusb -tv Shows USB devices

$ sudo dmidecode Shows hardware info from the BIOS

$ sudo hdparm -i /dev/sda # Shows info about disk sda

$ sudo hdparm -tT /dev/sda # Do a read speed test on disk sda

$ sudo badblocks -s /dev/sda # Test for unreadable blocks on disk sda


3. STATISTICS



$ top Displays the top CPU processes (Ctrl+C to exit)

$ vmstat 2 Displays virtual memory statistics

$ sudo tcpdump -i eth0 Captures all packets flows on interface eth0

$ sudo tcpdump -i eth0 'port 80' Monitors all traffic on port 80 ( HTTP )

$ lsof Lists all open files belonging to all active processes.

$ lsof -u myuser Lists files opened by specific user

$ watch df -h Shows changeable data continuously


4. USERS



$ id Shows the active user id with login and group

$ last Shows last logins on the system

$ who Shows who is logged on the system

$ groupadd admin Adds group "admin" 

$ useradd -c "Sam Tomshi" -g admin -m sam Creates user "sam" and adds to group "admin"

$ userdel sam Deletes user sam

$ adduser sam Adds user "sam"

$ usermod Modifies user information


5. FILE COMMANDS



$ cd .. To go up one level of the directory tree

$ cd Goes to $HOME directory

$ cd /test Changes to /test directory

$ ls gives the contents of a folder.

$ ls -a gives all the contents of a folder.

$ mkdir FolderName creates the folder FolderName.

$ cd Directory makes the Directory current directory

$ pwd prints the working directory

$ cp ~/Desktop/Berk/backups/science.txt . copy science.txt to the current directory

$ mv backups/science.txt /Desktop/Emi moves science.txt to folder Emi

$ rm temp.txt removes the temp.txt file

$ clear clear screen

$ cat science.txt Display contents of a file on the screen

$ less science.txt Displays on a different page ( type q to close the page)

$ less science.txt and then /name finds the occurences of name

$ head science.txt displays the first ten lines of the file

$ tail science.txt displays the last ten lines of the file

$ tail -20 science.txt displays the last 20 lines of the file

$ grep 'searchedkeyword' science.txt searches and finds the keyword in the file.(case sensitive)

$ grep -i SeaRchEdKeyWoRd science.txt case insensitive search

$ grep -i 'SeaRched Sentence is this one' science.txt case insensitive search

instead of i we can use;
-n precede each matching line with the line number
-v display those lines that do not match
-c print only the total count of matching lines

$ find -name "*.txt" -print  finds the text files in the current directory

$ diff a.txt b.txt gives the different lines

$ wc -w science.txt gives the word count

$ wc -l science.txt gives the line count

$ cat > list1
   pear
   banana
   ...
   ctrl+d

creates a list and we can print this list by using:

$ cat list1 command line.

$ cat biglist | grep p | sort gives sorted list elements which include p

$ sort < biglist > sortedlist sorts the biglist and writes it to the sortedlist

$ ls list* outputs the filenames starting with 'list'

$ ls *list outputs the filenames ending with 'list'

$ ls ?un outputs the filenames ending with 'un' but just one letter. (e.g. sun, gun, bun)

$ man ____ gives information about the command in the underlined section.

$ whatis ____ gives information about the command in the underlined section.

$ ls -l gives detailed information about the gfiles in the directory

u:user
g:group
o:other people
rwx: read write execute
rw: read write
r: read
x: execute

$ chmod u+x  TheFile adds writing permission to the user(owner) of TheFile

$ chmod go-rwx biglist to remove read write and execute permissions on the file biglist for the group and others

$ chmod 754 TheFile 7, 5, 4 represents the individual permissions for user, group, other (7:rwx, 5:rx, 4:r)

4 – stands for “read”
2 – stands for “write”
1 – stands for “execute”
0 – no permissions

$ du -s * The du command outputs the number of kilobyes used by each subdirectory.

$ df . The df command reports on the space left on the file system.

$ gzip science.txt Compresses into a gzip file

$ gunzip science.txt.gz De-compresses into the original file

$ tar cvf New.tar addthisfileintotar  Create a tar file called New and add this file.

$ tar xvf New.tar Extracts the tar file

$ zcat science.txt.gz reads zipped files without unzipping

$ file * Classifies the files in the current directory ( folder, text, gzip, etc.)

$ name=Berk
$ echo Hello $name  Prints 'Hello Berk'

$ sha1sum FileName | grep e509760917361307015  Compares the checksum of a downloaded file and the calculated one.

$ gpg -c file Encrypts file

$ gpg file.gpg Decrypts file


6. PROCESS RELATED




$ ps Displays your currently active processes

$ ps aux | grep 'telnet' Finds all process id related to telnet process

$ pmap Memory map of process

$ top Display all running processes

$ kill pid Kill process with mentioned pid id

$ killall proc Kill all processes named proc

sleep 10 & Sleeps at the background

kill 'JobNumber '  Terminates the job

jobs Display the jobs 

$ pkill processname Send signal to a process with its name

$ bg Resumes suspended jobs without bringing them to foreground

$ fg Brings the most recent job to foreground

$ fg n Brings job n to the foreground


7. FILE PERMISSION RELATED



$ chmod 777 /data/test.c Sets rwx permission for owner , rwx permission for group, rwx permission for world

$ chmod 755 /data/test.c Sets rwx permission for owner,rx for group and world

$ chown owner-user file Changes the owner of the file

$ chown owner-user:owner-group file-name Changes the owner and group owner of the file

$ chown owner-user:owner-group directory Changes the owner and group owner of the directory


8. NETWORK




$ ifconfig -a Display all network ports and ip address

$ ifconfig eth0 Display specific ethernet port ip address and details

$ ip addr show Display all network interfaces and ip address(available in iproute2 package,powerful than ifconfig)

$ ip address add 192.168.0.1 dev eth0 Set ip address

$ ethtool eth0 Linux tool to show ethernet status

$ mii-tool eth0 Linux tool to show ethernet status 

$ ping host Sends echo request to test connection

$ whois domain Get who is information for domain

$ dig domain Get DNS information for domain

$ dig -x host Reverse lookup host

$ host google.com Lookup DNS ip address for the name

$ hostname -i Lookup local ip address 

$ wget file  Download file

$ netstat -tupl Listing all active listening ports(tcp,udp,pid)

$ ssh user@host Connects to host as user

$ ssh -p port user@host Connects to host using specific port

$ telnet host Connects to the system using telnet port

9. COMPRESSION / ARCHIVES



$ tar cf home.tar home Creates tar named home.tar containing home/

$ tar xf file.tar Extracts the files from file.tar

$ tar czf file.tar.gz files Creates a tar with gzip compression

$ gzip file Compresses the file and renames it to file.gz


10. FILE TRANSFER





$ scp file.txt server2:/tmp  Secure copies file.txt to remote host /tmp folder

$ scp nixsavy@server2:/www/*.html /www/tmp  Copies *.html files from remote host to current system /www/tmp folder

$ scp -r nixsavy@server2:/www /www/tmp Copies all files and folders recursively from remote server to the current system /www/tmp folder

$ rsync -a /home/apps /backup/ Synchronizes source to destination

$ rsync -avz /home/apps linoxide@192.168.10.1:/backup Synchronizes files/directories between the local and remote system with compression enabled


Alright everyone, you have reached the end of the list. If you would like to download the PDF please share this post first and the button will be clickable afterwards.

Click to Download The PDF Version

You can also take a look at 40+ Commonly Used Bash Shortcuts from here. If you have any questions or if there is any command you would like us to add to the list, please leave a comment below. Happy coding!
Author:

Software Developer, Codemio Admin


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