Essential Linux Command-Line Tricks Every Sysadmin Should Know

This collection provides useful Linux command-line shortcuts for various tasks.

1. Check if a remote port is open for bash:

echo >/dev/tcp/8.8.8.8/53 && echo "open"

2. Send a process to the background:

Ctrl + z

3. Bring a process to the foreground:

fg

4. Generate a random hexadecimal string of length n:

openssl rand -hex n

5. Execute commands from a file in the current shell:

source /home/user/file.name

6. Extract the first 5 characters of a variable:

${variable:0:5}

7. SSH debug mode:

ssh -vvv user@ip_address

8. SSH with a PEM key:

ssh user@ip_address -i key.pem

9. Use wget to download an entire website directory structure to a local folder:

wget -r --no-parent --reject "index.html*" http://hostname/ -P /home/user/dirs

10. Create multiple directories at once:

mkdir -p /home/user/{test,test1,test2}

11. List the process tree including child processes:

ps axwef

12. Create a WAR file:

jar -cvf name.war file

13. Test disk write speed:

dd if=/dev/zero of=/tmp/output.img bs=8k count=256k; rm -rf /tmp/output.img

14. Test disk read speed:

hdparm -Tt /dev/sda

15. Get the MD5 hash of a text string:

echo -n "text" | md5sum

16. Validate XML format:

xmllint --noout file.xml

17. Extract a tar.gz archive into a new directory:

tar zxvf package.tar.gz -C new_dir

18. Retrieve HTTP headers with curl:

curl -I http://www.example.com

19. Change a file or directory timestamp (YYMMDDhhmm):

touch -t 0712250000 file

20. Download files via FTP using wget:

wget -m ftp://username:password@hostname

21. Generate a random password (example length 16 characters):

LANG=c < /dev/urandom tr -dc _A-Z-a-z-0-9 | head -c${1:-16};echo;

22. Quickly backup a file:

cp some_file_name{,.bkp}

23. Access a Windows shared directory:

smbclient -U "DOMAIN\user" //dc.domain.com/share/test/dir

24. Execute a command from history (line 100):

!100

25. Unzip a package to a directory:

unzip package_name.zip -d dir_name

26. Input multiple lines of text (Ctrl + D to exit):

cat > test.txt

27. Create an empty file or truncate an existing one:

> test.txt

28. Sync time with Ubuntu NTP server:

ntpdate ntp.ubuntu.com

29. Show all listening TCP4 ports with netstat:

netstat -lnt4 | awk '{print $4}' | cut -f2 -d: | grep -o '[0-9]*'

30. Convert a qcow2 image to raw format:

qemu-img convert -f qcow2 -O raw precise-server-cloudimg-amd64-disk1.img precise-server-cloudimg-amd64-disk1.raw

31. Repeatedly run a command and display its output (default every 2 seconds):

watch ps -ef

32. List the first 10 largest files:

lsof / | awk '{ if($7 > 1048576) print $7/1048576 "MB " $9 }' | sort -n -u | tail

33. Show remaining memory in MB:

free -m | grep cache | awk '/[0-9]/{ print $4" MB" }'

34. Open Vim and jump to the end of a file:

vim + some_file_name

35. Clone a specific branch (master) with Git:

git clone [email protected]:name/app.git -b master

36. Switch to another branch (develop) with Git:

git checkout develop

37. Delete a local branch (myfeature) with Git:

git branch -d myfeature

38. Delete a remote branch with Git:

git push origin :branchName

39. Push a new branch to the remote server:

git push -u origin mynewfeature

40. Print the last cat command from history:

!cat:p

41. Run the last cat command from history:

!cat

42. Find all empty subdirectories under /home/user:

find /home/user -maxdepth 1 -type d -empty

43. Show lines 50‑60 of test.txt:

< test.txt sed -n '50,60p'

44. Re‑execute the last command with sudo (e.g., sudo mkdir /root/test):

sudo !!

45. Create a temporary RAM filesystem (ramdisk) after creating /tmpram directory:

mount -t tmpfs tmpfs /tmpram -o size=512m

46. Grep whole words:

grep -w "name" test.txt

47. Append text to a file with elevated privileges:

echo "some text" | sudo tee -a /path/file

48. List all kill signal names:

kill -l

49. Prevent the last session from being recorded in bash history:

kill -9 $$

50. Scan a network for open ports:

nmap -p 8081 172.20.0.0/16

51. Set Git email address:

git config --global user.email "[email protected]"

52. Sync with master when you have unpublished commits:

git pull --rebase origin master

53. Move all files containing "txt" in their name to /home/user:

find -iname "*txt*" -exec mv -v {} /home/user \;

54. Display two files side by side, line by line:

paste test.txt test1.txt

55. Show a progress bar for a file with pv:

pv data.log

56. Send data to a Graphite server using netcat:

echo "hosts.sampleHost 10 `date +%s`" | nc 192.168.200.2 3000

57. Convert tabs to spaces:

expand test.txt > test1.txt

58. Skip bash history for a command:

< space >cmd

59. Return to the previous working directory:

cd -

60. Split a large tar.gz file into 100 MB parts and re‑assemble:

split –b 100m /path/to/large/archive /path/to/output/files
cat files* > archive

61. Get HTTP status code with curl:

curl -sL -w "%{http_code}
" www.example.com -o /dev/null

62. Run MySQL secure installation to set root password and harden security:

/usr/bin/mysql_secure_installation

63. When Ctrl + C does not work, use Ctrl + \:

Ctrl + \

64. Get the owner of a file:

stat -c %U file.txt

65. List block devices with filesystem information:

lsblk -f

66. Find files whose names end with a space:

find . -type f -exec egrep -l " +$" {} \;

67. Find files whose names contain a tab character:

find . -type f -exec egrep -l '\t' {} \;

68. Print a line of 100 equal signs:

printf '%100s
' | tr ' ' =