Linux Commands

📁 Linux Commands – File Operations & Navigation

Topic	Question	Answer
Linux	Get all files realpaths	find . -exec realpath {} +
Linux	Find file by name	find . -name "file.txt"
Linux	Find file name case insensitive	find . -iname "file.txt"
Linux	Find all *.txt files	find . -name "*.txt"
Linux	Find file containing text in name	find . -name "*report*"
Linux	Remove empty directories	find . -type d -empty -delete
Linux	Delete all files of specific format	find . -name "*.log" -delete
Linux	Find directories	find . -type d -name "foldername"
Linux	Find modified in last 1 day	find . -mtime -1
Linux	Find modified more than 7 days ago	find . -mtime +7
Linux	Find modified in last 60 minutes	find . -mmin -60
Linux	Find accessed in last N days	find . -atime -N
Linux	Find by size greater than 100mb	find . -size +100M
Linux	Find by size less than 10mb	find . -size -10M
Linux	Find by exact size	find . -size 1024c
Linux	Find empty files	find . -size 0
Linux	Find file + grep	find . -type f -name "*.sv" -exec grep -l "uvm_component" {} \;
Linux	Delete all empty files	find . -type f -empty -delete
Linux	Find and move files	find . -name "*.bak" -exec mv {} /backup/ \;
Linux	Find files owned by user	find . -user username
Linux	Find files by permissions	find . -perm 644
Linux	Find writable files	find . -perm -200
Linux	Find executable files	find . -type f -executable
Linux	Find symbolic links	find . -type l
Linux	Find broken symbolic links	find . -xtype l
Linux	Find and count files	find . -type f | wc -l
Linux	Find files excluding directory	find . -path ./exclude -prune -o -name "*.txt"
Linux	Find by multiple extensions	find . -name "*.sv" -o -name "*.v"
Linux	Clear terminal	CTRL + l or clear
Linux	Exit terminal	CTRL + d or exit
Linux	List files with details	ls -lah
Linux	List files sorted by time	ls -lt
Linux	List files sorted by size	ls -lS
Linux	List files reverse order	ls -lr
Linux	List with inode numbers	ls -li
Linux	List only directories	ls -d */
Linux	List with full path	ls -d $PWD/*
Linux	List recursively	ls -R
Linux	List one per line	ls -1
Linux	List with file type indicators	ls -F
Linux	Show disk usage	du -sh *
Linux	Show disk usage sorted	du -sh * | sort -h
Linux	Show directory size	du -sh directory/
Linux	Show total disk usage	du -ch
Linux	Show free disk space	df -h
Linux	Show inode usage	df -i
Linux	Show specific filesystem	df -h /dev/sda1
Linux	Create directory	mkdir dirname
Linux	Create directory with parents	mkdir -p path/to/directory
Linux	Create multiple directories	mkdir dir1 dir2 dir3
Linux	Create directory with permissions	mkdir -m 755 dirname
Linux	Remove empty directory	rmdir dirname
Linux	Remove directory recursively	rm -rf directory_name
Linux	Remove directory interactively	rm -ri directory_name
Linux	Copy file	cp source.txt dest.txt
Linux	Copy files recursively	cp -r source_dir dest_dir
Linux	Copy preserving attributes	cp -p file dest
Linux	Copy with verbose output	cp -v file dest
Linux	Copy force overwrite	cp -f file dest
Linux	Copy only if newer	cp -u file dest
Linux	Copy creating backup	cp --backup file dest
Linux	Move/Rename files	mv old_name new_name
Linux	Move multiple files	mv file1 file2 file3 dest/
Linux	Move with backup	mv --backup file dest
Linux	Move no clobber	mv -n file dest
Linux	Create hard link	ln file linkname
Linux	Create symbolic link	ln -s /path/to/file linkname
Linux	Create symbolic link force	ln -sf /path/to/file linkname
Linux	Show current directory	pwd
Linux	Show physical directory (resolve symlinks)	pwd -P
Linux	Change to home directory	cd ~ or cd
Linux	Go to previous directory	cd -
Linux	Go up one level	cd ..
Linux	Go up two levels	cd ../..
Linux	Change to root	cd /
Linux	Touch create file	touch newfile.txt
Linux	Touch update timestamp	touch existing.txt
Linux	Touch with specific time	touch -t 202401011200 file.txt
Linux	Touch set access time	touch -a file.txt
Linux	Touch set modification time	touch -m file.txt

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🔍 Linux Commands – Text Processing & Search

Topic	Question	Answer
Linux	Search text in files	grep "pattern" file.txt
Linux	Search recursively	grep -r "pattern" directory/
Linux	Search case insensitive	grep -i "pattern" file.txt
Linux	Search with line numbers	grep -n "pattern" file.txt
Linux	Search with context	grep -C 3 "pattern" file.txt
Linux	Search with before context	grep -B 2 "pattern" file.txt
Linux	Search with after context	grep -A 2 "pattern" file.txt
Linux	Count matching lines	grep -c "pattern" file.txt
Linux	Inverse match	grep -v "pattern" file.txt
Linux	Search whole word	grep -w "word" file.txt
Linux	Search multiple patterns	grep -e "pat1" -e "pat2" file.txt
Linux	Search with regex	grep -E "regex" file.txt or egrep
Linux	Search with extended regex	grep -P "perl_regex" file.txt
Linux	Show only matching part	grep -o "pattern" file.txt
Linux	Search in multiple files	grep "pattern" *.txt
Linux	Search with filename only	grep -l "pattern" *.txt
Linux	Search without filename	grep -h "pattern" *.txt
Linux	Search binary files	grep -a "pattern" file
Linux	Search excluding files	grep --exclude="*.log" "pattern" *
Linux	Search excluding directory	grep --exclude-dir=".git" -r "pattern"
Linux	View file contents	cat file.txt
Linux	View with line numbers	cat -n file.txt
Linux	View showing tabs	cat -T file.txt
Linux	View showing ends	cat -E file.txt
Linux	Concatenate files	cat file1 file2 > combined.txt
Linux	View first 10 lines	head file.txt
Linux	View first N lines	head -n 20 file.txt
Linux	View first N bytes	head -c 100 file.txt
Linux	View multiple files	head file1 file2
Linux	View last 10 lines	tail file.txt
Linux	View last N lines	tail -n 50 file.txt
Linux	View from line N	tail -n +10 file.txt
Linux	Follow file real-time	tail -f file.log
Linux	Follow with retry	tail -F file.log
Linux	Follow multiple files	tail -f file1 file2
Linux	View page by page	less file.txt
Linux	View with more	more file.txt
Linux	Count lines	wc -l file.txt
Linux	Count words	wc -w file.txt
Linux	Count characters	wc -c file.txt
Linux	Count bytes	wc -c file.txt
Linux	Count longest line	wc -L file.txt
Linux	Sort file	sort file.txt
Linux	Sort numerically	sort -n file.txt
Linux	Sort reverse	sort -r file.txt
Linux	Sort by column	sort -k 2 file.txt
Linux	Sort case insensitive	sort -f file.txt
Linux	Sort unique	sort -u file.txt
Linux	Sort by month	sort -M file.txt
Linux	Sort human numeric	sort -h file.txt
Linux	Remove duplicates	sort file.txt | uniq
Linux	Count duplicates	sort file.txt | uniq -c
Linux	Show only duplicates	sort file.txt | uniq -d
Linux	Show only unique	sort file.txt | uniq -u
Linux	Compare files	diff file1.txt file2.txt
Linux	Compare side by side	diff -y file1.txt file2.txt
Linux	Compare unified format	diff -u file1.txt file2.txt
Linux	Compare ignore whitespace	diff -w file1.txt file2.txt
Linux	Compare ignore case	diff -i file1.txt file2.txt
Linux	Compare directories	diff -r dir1/ dir2/
Linux	Show file type	file filename
Linux	Show MIME type	file -i filename
Linux	Cut by delimiter	cut -d ',' -f 1 file.csv
Linux	Cut by character position	cut -c 1-10 file.txt
Linux	Cut by byte	cut -b 1-10 file.txt
Linux	Paste files	paste file1 file2
Linux	Paste with delimiter	paste -d ',' file1 file2
Linux	Column formatting	column -t file.txt
Linux	Translate characters	tr 'a-z' 'A-Z' < file.txt
Linux	Delete characters	tr -d '0-9' < file.txt
Linux	Squeeze repeats	tr -s ' ' < file.txt

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🛠️ Linux Commands – System & Process Management

Topic	Question	Answer
Linux	Archive files	tar -czf archive.tar.gz directory/
Linux	Archive with bzip2	tar -cjf archive.tar.bz2 directory/
Linux	Archive verbose	tar -czvf archive.tar.gz directory/
Linux	Extract archive	tar -xzf archive.tar.gz
Linux	Extract to directory	tar -xzf archive.tar.gz -C /path/
Linux	List archive contents	tar -tzf archive.tar.gz
Linux	Extract single file	tar -xzf archive.tar.gz file.txt
Linux	Compress file with gzip	gzip file.txt
Linux	Decompress gzip	gunzip file.txt.gz
Linux	Keep original with gzip	gzip -k file.txt
Linux	Compress with bzip2	bzip2 file.txt
Linux	Decompress bzip2	bunzip2 file.txt.bz2
Linux	Compress with xz	xz file.txt
Linux	Decompress xz	unxz file.txt.xz
Linux	Create zip	zip archive.zip file1 file2
Linux	Create zip recursive	zip -r archive.zip directory/
Linux	Extract zip	unzip archive.zip
Linux	List zip contents	unzip -l archive.zip
Linux	Check processes	ps aux
Linux	Check process tree	ps auxf or pstree
Linux	Check processes for user	ps -u username
Linux	Find process by name	ps aux | grep process_name
Linux	Show process by PID	ps -p PID
Linux	Show all threads	ps -eLf
Linux	Kill process	kill PID
Linux	Force kill	kill -9 PID or kill -SIGKILL PID
Linux	Terminate gracefully	kill -15 PID or kill -SIGTERM PID
Linux	Kill process by name	pkill process_name
Linux	Kill all by name	killall process_name
Linux	Show running processes	top
Linux	Show processes with htop	htop
Linux	Sort top by memory	Press M in top
Linux	Sort top by CPU	Press P in top
Linux	Kill from top	Press k in top
Linux	Show system uptime	uptime
Linux	Show load average	uptime or cat /proc/loadavg
Linux	Show memory	free -h
Linux	Show memory in MB	free -m
Linux	Show memory continuous	free -s 2
Linux	Show swap usage	swapon --show
Linux	Show current user	whoami
Linux	Show effective user ID	id
Linux	Show all logged users	who
Linux	Show detailed user info	w
Linux	Show last logins	last
Linux	Show failed logins	lastb
Linux	Show login history	lastlog
Linux	Change permissions	chmod 755 file.sh
Linux	Change recursively	chmod -R 755 directory/
Linux	Add execute permission	chmod +x file.sh
Linux	Remove write permission	chmod -w file.txt
Linux	Set user permissions	chmod u+rwx file
Linux	Set group permissions	chmod g+rw file
Linux	Set other permissions	chmod o+r file
Linux	Change ownership	chown user:group file.txt
Linux	Change owner only	chown user file.txt
Linux	Change group only	chgrp group file.txt
Linux	Change ownership recursive	chown -R user:group directory/
Linux	Make file executable	chmod +x script.sh
Linux	View file permissions	ls -l file.txt
Linux	View octal permissions	stat -c "%a %n" file
Linux	Set setuid bit	chmod u+s file
Linux	Set setgid bit	chmod g+s file
Linux	Set sticky bit	chmod +t directory/
Linux	Change file ACL	setfacl -m u:user:rwx file
Linux	View file ACL	getfacl file

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🌐 Linux Commands – Network & Remote

Topic	Question	Answer
Linux	Download file	wget URL
Linux	Download with curl	curl -O URL
Linux	Download to file	curl -o filename URL
Linux	Download continue	wget -c URL
Linux	Download in background	wget -b URL
Linux	Download with user agent	wget --user-agent="agent" URL
Linux	Download FTP	wget ftp://server/file
Linux	Check connectivity	ping google.com
Linux	Ping count	ping -c 4 google.com
Linux	Ping with interval	ping -i 2 google.com
Linux	Traceroute	traceroute google.com
Linux	DNS lookup	nslookup google.com
Linux	DNS with dig	dig google.com
Linux	Reverse DNS	dig -x IP_ADDRESS
Linux	Show network interfaces	ifconfig or ip addr
Linux	Show specific interface	ifconfig eth0
Linux	Bring interface up	sudo ifconfig eth0 up
Linux	Bring interface down	sudo ifconfig eth0 down
Linux	Show routing table	route -n or ip route
Linux	Add route	sudo route add -net 192.168.1.0/24 gw 192.168.1.1
Linux	Show listening ports	netstat -tuln or ss -tuln
Linux	Show all connections	netstat -a
Linux	Show TCP connections	netstat -t
Linux	Show UDP connections	netstat -u
Linux	Show with PID	netstat -tulnp
Linux	Show statistics	netstat -s
Linux	Show network sockets	ss -s
Linux	Test port	nc -zv host port or telnet host port
Linux	Secure copy to remote	scp file.txt user@host:/path/
Linux	Secure copy from remote	scp user@host:/path/file.txt .
Linux	SCP with port	scp -P 2222 file.txt user@host:/path/
Linux	SCP recursive	scp -r directory/ user@host:/path/
Linux	SSH to remote	ssh user@hostname
Linux	SSH with port	ssh -p 2222 user@hostname
Linux	SSH with key	ssh -i keyfile user@hostname
Linux	SSH execute command	ssh user@host 'command'
Linux	SSH tunnel	ssh -L localport:remotehost:remoteport user@host
Linux	Rsync files	rsync -avz source/ destination/
Linux	Rsync with progress	rsync -avz --progress source/ dest/
Linux	Rsync with delete	rsync -avz --delete source/ dest/
Linux	Rsync dry run	rsync -avz --dry-run source/ dest/
Linux	Rsync over SSH	rsync -avz -e ssh source/ user@host:dest/
Linux	Show ARP table	arp -a
Linux	Flush DNS cache	sudo systemd-resolve --flush-caches
Linux	Show hostname	hostname
Linux	Show FQDN	hostname -f
Linux	Show IP address	hostname -I
Linux	Set hostname	sudo hostnamectl set-hostname newname

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⚙️ Linux Commands – Shell & Environment

Topic	Question	Answer
Linux	Search command history	history | grep "keyword"
Linux	Execute previous command	!!
Linux	Execute command from history	!number
Linux	Execute last command starting with	!string
Linux	Clear command history	history -c
Linux	Delete history entry	history -d number
Linux	Show environment variables	printenv or env
Linux	Set environment variable	export VAR_NAME="value"
Linux	Unset environment variable	unset VAR_NAME
Linux	Show specific variable	echo $VAR_NAME
Linux	Show all variables	set
Linux	Show PATH	echo $PATH
Linux	Add to PATH	export PATH=$PATH:/new/path
Linux	Show shell	echo $SHELL
Linux	Find which command	which command_name
Linux	Show command location	whereis command_name
Linux	Show command type	type command_name
Linux	Show all locations	which -a command_name
Linux	Create alias	alias ll='ls -la'
Linux	Show all aliases	alias
Linux	Remove alias	unalias ll
Linux	Permanent alias	Add to ~/.bashrc or ~/.bash_aliases
Linux	Source bashrc	source ~/.bashrc or . ~/.bashrc
Linux	Run command in background	command &
Linux	Bring to foreground	fg
Linux	Bring specific job	fg %1
Linux	Send to background	bg
Linux	List background jobs	jobs
Linux	Disown job	disown %1
Linux	Redirect output	command > output.txt
Linux	Append output	command >> output.txt
Linux	Redirect errors	command 2> error.log
Linux	Redirect both	command > output.txt 2>&1
Linux	Redirect to null	command > /dev/null
Linux	Redirect both to null	command > /dev/null 2>&1
Linux	Pipe commands	command1 | command2
Linux	Tee to file and stdout	command | tee output.txt
Linux	Tee append	command | tee -a output.txt
Linux	Run multiple commands	command1 && command2
Linux	Run if previous fails	`command1 |
Linux	Run sequentially	command1 ; command2
Linux	Show date	date
Linux	Show date formatted	date "+%Y-%m-%d %H:%M:%S"
Linux	Show date UTC	date -u
Linux	Show calendar	cal
Linux	Show specific month	cal 12 2024
Linux	Show year calendar	cal 2024
Linux	Calculate MD5	md5sum file.txt
Linux	Calculate SHA1	sha1sum file.txt
Linux	Calculate SHA256	sha256sum file.txt
Linux	Verify checksum	md5sum -c checksums.txt
Linux	Base64 encode	base64 file.txt
Linux	Base64 decode	base64 -d encoded.txt

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📝 Linux Commands – Text Editors (sed, awk)

Topic	Question	Answer
Linux	Replace text in files	sed 's/old/new/g' file.txt
Linux	Replace in-place	sed -i 's/old/new/g' file.txt
Linux	Replace with backup	sed -i.bak 's/old/new/g' file.txt
Linux	Delete lines	sed '/pattern/d' file.txt
Linux	Delete empty lines	sed '/^$/d' file.txt
Linux	Print specific lines	sed -n '10,20p' file.txt
Linux	Replace on specific line	sed '5s/old/new/' file.txt
Linux	Insert line before	sed '/pattern/i\New line' file.txt
Linux	Append line after	sed '/pattern/a\New line' file.txt
Linux	Print specific columns	awk '{print $1, $3}' file.txt
Linux	Print with separator	awk -F',' '{print $1}' file.csv
Linux	Sum column values	awk '{sum+=$1} END {print sum}' file.txt
Linux	Print line numbers	awk '{print NR, $0}' file.txt
Linux	Filter by condition	awk '$3 > 100' file.txt
Linux	Print number of fields	awk '{print NF}' file.txt
Linux	Pattern matching	awk '/pattern/ {print}' file.txt
Linux	Begin and end	awk 'BEGIN {print "Start"} {print} END {print "End"}' file