Essential Linux Bash Tips and Commands Every Sysadmin Should Know

This article collects a wide range of useful Linux Bash commands that can help system administrators and developers perform common tasks more efficiently.

Check if a remote port is open: echo >/dev/tcp/8.8.8.8/53 && echo "open" Suspend a process: Ctrl+z Bring a suspended process to the foreground: fg Generate a random hexadecimal string (n characters): openssl rand -hex n Source a file in the current shell (e.g., .bashrc, .bash_profile): source /home/user/file.name Extract the first five characters of a variable: ${variable:0:5} Enable SSH debug mode: ssh -vvv user@ip_address Connect via SSH using a PEM key: ssh user@ip_address -i key.pem Download a full directory tree with wget:

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

Create multiple directories at once: mkdir -p /home/user/{test,test1,test2} List processes in a tree view: ps axwef Create a WAR file: jar -cvf name.war file Test disk write speed:

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

Test disk read speed: hdparm -Tt /dev/sda Compute MD5 of a text string: echo -n "text" | md5sum Validate XML syntax: xmllint --noout file.xml Extract a tar.gz archive to a specific directory: tar zxvf package.tar.gz -C new_dir Get HTTP headers with curl: curl -I http://www.example.com Change file timestamps (YYMMDDhhmm format): touch -t 0712250000 file Download from FTP with wget: wget -m ftp://username:password@hostname Generate a random password (16 characters):

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

Quickly backup a file (adds .bkp extension): cp some_file_name{,.bkp} Access a Windows share: smbclient -U "DOMAINuser" //dc.domain.com/share/test/dir Rerun a command from history (e.g., the 100th entry): !100 Unzip an archive to a directory: unzip package_name.zip -d dir_name Append text to a file with elevated privileges: echo "some text" | sudo tee -a /path/file List all supported kill signals: kill -l Generate a base64‑encoded random password (16 bytes): openssl rand -base64 16 Prevent the last command from being recorded in Bash history: kill -9 $$ Scan a network for open ports: nmap -p 8081 172.20.0.0/16 Configure Git email: git config --global user.email "[email protected]" Rebase the current branch onto master: git pull --rebase origin master Move all files containing "txt" in their name to /home/user: find -iname "*txt*" -exec mv -v {} /home/user \; Merge corresponding lines from two files: paste test.txt test1.txt Show a progress bar for a file: pv data.log Send data to a server with netcat:

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

Convert tabs to spaces: expand test.txt > test1.txt Print a horizontal line of "=" characters: printf '%100sn' | tr ' ' = Set up a temporary RAM disk (512 MiB): mount -t tmpfs tmpfs /tmpram -o size=512m Search for whole-word matches with grep: grep -w "name" test.txt List all users: getent passwd Remount the root filesystem as read‑write: mount -o remount,rw / Bind‑mount a directory (useful when symlinks fail): mount --bind /source /destination Send a DNS dynamic update: nsupdate < Recursively grep a pattern in all directories: grep -r "some_text" /path/to/dir List the ten largest open files (in MB):

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

Show free memory in MB (cache column): free -m | grep cache | awk '/[0-9]/{ print $4" MB" }' Open Vim at the end of a file: vim + some_file_name Clone a specific Git branch (master): git clone [email protected]:name/app.git -b master Switch to another Git branch (develop): git checkout develop Delete a local Git branch (myfeature): git branch -d myfeature Delete a remote Git branch: git push origin :branchName Push a new branch to remote: git push -u origin mynewfeature Run the last cat command from history: !cat Find empty subdirectories under /home/user: find /home/user -maxdepth 1 -type d -empty Extract lines 50‑60 from test.txt: < test.txt sed -n '50,60p' Rerun the previous command with sudo: sudo !! Find files with trailing spaces in their names: find . -type f -exec egrep -l " +$" "{}" \; Find files indented with tabs: find . -type f -exec egrep -l $'\t' "{}" \; Print a horizontal line of "=" characters (alternative): printf '%100sn' | tr ' ' = Split a large tar.gz into 100 MiB pieces and reassemble:

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

Get HTTP status code with curl: curl -sL -w "%{http_code}\n" www.example.com -o /dev/null Force‑quit a hung process when Ctrl+C fails: Ctrl+\ Retrieve the owner of a file: stat -c %U file.txt List block devices with filesystem info:

lsblk -f