Essential Linux Command Cheat Sheet: 73 Handy Bash Tips

1. Check if remote port is open for bash: echo >/dev/tcp/8.8.8.8/53 && echo "open" 2. Send a process to background: Ctrl+z 3. Bring a background process to foreground: fg 4. Generate a random hexadecimal string of n characters: 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 (verbose): ssh -vvv user@ip_address 8. SSH with a PEM key: ssh user@ip_address -i key.pem 9. Download an entire website directory structure with wget:

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 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 MD5 hash of a text string: echo -n "text" | md5sum 16. Validate XML format: xmllint --noout file.xml 17. Extract a tar.gz archive to 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 file or directory timestamp (YYMMDDhhmm): touch -t 0712250000 file 20. Perform FTP download with wget: wget -m ftp://username:password@hostname 21. Generate a random password (default 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 share directory: smbclient -U "DOMAIN\user" //dc.domain.com/share/test/dir 24. Execute a command from history (line 100): !100 25. Unzip an archive 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. List all listening TCP4 ports:

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

30. Convert 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 show output (default every 2 seconds): watch ps -ef 32. List all users: getent passwd 33. Remount root filesystem as read/write: mount -o remount,rw / 34. Bind-mount a directory (no symlink): mount --bind /source /destination 35. Dynamically update DNS server:

nsupdate <<EOF
update add $HOST 86400 A $IP
send
EOF

36. Recursively grep through all directories: grep -r "some_text" /path/to/dir 37. List top 10 largest files:

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

38. Show remaining memory in MB: free -m | grep cache | awk '/[0-9]/{ print $4" MB" }' 39. Open Vim and jump to end of file: vim + some_file_name 40. Clone a specific Git branch (master): git clone [email protected]:name/app.git -b master 41. Switch to another Git branch (develop): git checkout develop 42. Delete a Git branch (myfeature): git branch -d myfeature 43. Delete a remote Git branch: git push origin :branchName 44. Push a new branch to remote: git push -u origin mynewfeature 45. Print the last "cat" command from history: !cat:p 46. Execute the last "cat" command from history: !cat 47. Find all empty subdirectories under /home/user: find /home/user -maxdepth 1 -type d -empty 48. Show lines 50‑60 of test.txt: sed -n '50,60p' test.txt 49. Run the previous command with sudo (e.g., mkdir): sudo !! 50. Create a temporary RAM disk (512 MiB): mount -t tmpfs tmpfs /tmpram -o size=512m 51. Grep whole words: grep -w "name" test.txt 52. Append text to a file with elevated privileges: echo "some text" | sudo tee -a /path/file 53. List all kill signal names: kill -l 54. Terminate the current Bash session: kill -9 $$ 55. Scan network for open ports (e.g., 8081): nmap -p 8081 172.20.0.0/16 56. Set Git user email: git config --global user.email "[email protected]" 57. Rebase local commits onto upstream master: git pull --rebase origin master 58. Move all files containing "txt" in their name to /home/user: find -iname "*txt*" -exec mv -v {} /home/user \; 59. Display files side‑by‑side (columnar): paste test.txt test1.txt 60. Show a progress bar for a file: pv data.log 61. Send metrics to a Graphite server via netcat:

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

62. Convert tabs to spaces: expand test.txt > test1.txt 63. Skip Bash history for a command: < space >cmd 64. Return to previous working directory: cd - 65. Split a large tar.gz into 100 MiB parts and reassemble:

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

66. Get HTTP status code with curl: curl -sL -w "%{http_code}\n" www.example.com -o /dev/null 67. Secure MySQL installation and set root password: /usr/bin/mysql_secure_installation 68. Force‑quit a hanging process when Ctrl+C fails: Ctrl+\ 69. Get file owner name: stat -c %U file.txt 70. List block devices with filesystem info: lsblk -f 71. Find files whose names end with a space: find . -type f -exec egrep -l " +$" {} \; 72. Find files with tab characters in their names: find . -type f -exec egrep -l $'\t' {} \; 73. Print a line of 100 equal signs:

printf '%100s
' | tr ' ' =