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Basic Unix/Linux Commands

2025-July-09

📁 File Commands

Command	Description	Example
`ls`	List directory contents	`ls`
`ls -al`	List all files with details	`ls -al`
`ls -lt`	List by modification time	`ls -lt`
`cd dir`	Change directory	`cd /var/log`
`cd`	Go to home	`cd`
`pwd`	Print current directory	`pwd`
`mkdir dir`	Make a directory	`mkdir new_folder`
`cat >file`	Create a file	`cat > notes.txt`
`more file`	View file page by page	`more notes.txt`
`head file`	First 10 lines	`head notes.txt`
`tail file`	Last 10 lines	`tail notes.txt`
`tail -f file`	Monitor file live	`tail -f /var/log/syslog`
`touch file`	Create empty file	`touch empty.txt`
`rm file`	Delete a file	`rm notes.txt`
`rm -r dir`	Delete a directory	`rm -r old_folder`
`rm -f file`	Force delete	`rm -f locked.txt`
`rm -rf dir`	Force delete dir	`rm -rf /tmp/cache`

⚙️ Process Management

Command	Description	Example
`cp file1 file2`	Copy a file	`cp a.txt b.txt`
`cp -r dir1 dir2`	Copy directory	`cp -r src/ backup/`
`mv file1 file2`	Move/rename file	`mv a.txt b.txt`
`ln -s file link`	Symbolic link	`ln -s /var/log/syslog loglink`
`ps`	Show running processes	`ps aux`
`top`	Real-time process list	`top`
`kill pid`	Kill by PID	`kill 1234`
`killall proc`	Kill by name	`killall firefox`
`pkill pattern`	Kill by pattern	`pkill python`
`bg`	Resume job in background	`bg`
`fg`	Foreground last job	`fg`
`fg n`	Foreground job n	`fg %1`

🖥️ System Info

Command	Description	Example
`date`	Current date/time	`date`
`cal`	Monthly calendar	`cal`
`uptime`	System uptime	`uptime`
`w`	Who is logged in	`w`
`whoami`	Current user	`whoami`
`finger user`	User info	`finger alice`
`uname -a`	System info	`uname -a`
`cat /proc/cpuinfo`	CPU info	`cat /proc/cpuinfo`
`cat /proc/meminfo`	Memory info	`cat /proc/meminfo`
`man command`	Manual page	`man ls`
`df`	Disk usage	`df -h`
`du`	Directory usage	`du -sh /home/user/`
`free`	Memory/swap usage	`free -m`
`whereis app`	App locations	`whereis python`
`which app`	Path to command	`which python`

📦 Compression

Command	Description	Example
`tar cf file.tar file`	Create tar	`tar cf archive.tar file.txt`
`tar xf file.tar`	Extract tar	`tar xf archive.tar`
`tar czf file.tar.gz files`	Create gzipped tar	`tar czf archive.tar.gz *.txt`
`tar xzf file.tar.gz`	Extract gzipped tar	`tar xzf archive.tar.gz`
`tar cjf file.tar.bz2`	Create bzip2 archive	`tar cjf archive.tar.bz2 *.log`
`tar xjf file.tar.bz2`	Extract bzip2	`tar xjf archive.tar.bz2`
`gzip file`	Compress file	`gzip notes.txt`
`gzip -d file.gz`	Decompress	`gzip -d notes.txt.gz`

🌐 Network Related

Command	Description	Example
`ping host`	Ping host	`ping google.com`
`whois domain`	Domain info	`whois openai.com`
`dig domain`	DNS info	`dig openai.com`
`dig -x host`	Reverse DNS	`dig -x 8.8.8.8`
`wget file`	Download file	`wget https://example.com/file.txt`
`wget -c file`	Resume download	`wget -c file.txt`

⌨️ Shortcuts

Shortcut	Action
`Ctrl+C`	Stop command
`Ctrl+Z`	Pause command
`Ctrl+D`	End input/logout
`Ctrl+W`	Delete last word
`Ctrl+U`	Delete whole line
`Ctrl+R`	Search history
`!!`	Repeat last command
`exit`	Exit terminal

🔐 Permissions & Ownership

Command	Description	Example
`chmod 755 file`	Set permissions	`chmod 755 script.sh`
`su`	Become root	`su`
`sudo command`	Run as root	`sudo apt update`
`chown user file`	Change owner	`chown alice notes.txt`
`chgrp group file`	Change group	`chgrp staff notes.txt`