Linux Commands

Comprehensive Linux Commands Cheat Sheet for Cybersecurity Professionals

🔍

Examples:

Command	Description & Usage
Basic Commands
ls	List directory contents. Examples: `ls` - List files `ls -la` - List all files in long format `ls -lh` - List with human-readable sizes Use `ls --color=auto` for colorized output.
pwd	Print working directory (shows current location). Example: `pwd`
cd	Change directory. Examples: `cd /home/user` - Go to specific directory `cd ..` - Go up one directory `cd ~` - Go to home directory `cd -` - Go to previous directory
mkdir	Create new directory. Examples: `mkdir new_folder` `mkdir -p parent/child/grandchild` - Create nested directories
mv	Move or rename files and directories. Examples: `mv file.txt /new/location` - Move file `mv oldname.txt newname.txt` - Rename file `mv -i file.txt dir/` - Interactive mode (asks before overwrite)
cp	Copy files and directories. Examples: `cp file.txt /copy/location` `cp -r directory/ backup/` - Copy directories recursively `cp -p file.txt backup/` - Preserve permissions and timestamps
rm	Remove files or directories. Examples: `rm file.txt` - Remove file `rm -r directory/` - Remove directory recursively `rm -f file.txt` - Force removal without prompting Use with caution: `rm -rf` can cause data loss if used improperly.
touch	Create an empty file or update timestamps. Example: `touch newfile.txt`
clear	Clear terminal screen. Example: `clear` or `Ctrl+L`
echo	Display a line of text. Examples: `echo "Hello World"` `echo $PATH` - Print environment variable `echo "text" > file.txt` - Output to file (overwrite) `echo "text" >> file.txt` - Append to file
man	Display manual pages for commands. Example: `man ls` - Display manual for ls command
File Viewing & Manipulation
cat	View file contents. Examples: `cat file.txt` `cat -n file.txt` - Show line numbers `cat file1.txt file2.txt` - Concatenate files
less	View file contents page by page. Example: `less file.txt` Use space to scroll forward, 'b' to go back, 'q' to quit.
head	View beginning of a file. Examples: `head file.txt` - Show first 10 lines `head -n 20 file.txt` - Show first 20 lines
tail	View end of a file. Examples: `tail file.txt` - Show last 10 lines `tail -n 20 file.txt` - Show last 20 lines `tail -f log.txt` - Follow file changes in real-time
grep	Search text in files. Examples: `grep "pattern" file.txt` `grep -i "pattern"` - Case insensitive `grep -r "pattern" directory/` - Recursive search `grep -v "pattern" file.txt` - Invert match (lines not containing pattern)
find	Search for files in a directory hierarchy. Examples: `find /home -name "*.txt"` - Find by name `find / -type f -size +100M` - Find files larger than 100MB `find /var/log -mtime -7` - Files modified in last 7 days `find . -perm -u=s` - Find SUID files
locate	Find files by name using database. Examples: `locate filename` `sudo updatedb` - Update the locate database
diff	Compare files line by line. Example: `diff file1.txt file2.txt`
file	Determine file type. Example: `file filename`
wc	Count lines, words, and characters. Examples: `wc file.txt` - Show all counts `wc -l file.txt` - Line count only
System Information
uname	Show system information. Examples:
whoami	Show current username. Example: `whoami`
uptime	Show system uptime and load averages. Example: `uptime`
free	Display memory usage. Examples: `free` `free -h` - Human readable format `free -m` - In megabytes
df	Disk space usage. Examples: `df -h` - Human readable format `df -i` - Show inodes
du	Estimate file space usage. Examples: `du -sh directory/` - Summary in human-readable format `du -ah` - All files with sizes
lscpu	Display CPU information. Example: `lscpu`
lsblk	List block devices. Example: `lsblk`
lshw	List hardware information. Example: `sudo lshw -short`
history	Show command history. Examples: `history` `history \| grep "search"` `!123` - Execute command from history with ID 123
User Management
useradd	Add new user. Examples: `sudo useradd username` `sudo useradd -m -s /bin/bash username` - Create home dir and set shell
userdel	Delete user. Examples: `sudo userdel username` `sudo userdel -r username` - Remove home directory too
passwd	Change user password. Examples: `passwd` - Change your password `sudo passwd username` - Change another user's password
usermod	Modify user account. Examples: `sudo usermod -aG groupname username` - Add user to group `sudo usermod -s /bin/bash username` - Change shell
groupadd	Create new group. Example: `sudo groupadd groupname`
groups	Show groups a user belongs to. Example: `groups username`
who	Show who is logged in. Example: `who`
w	Show who is logged in and what they're doing. Example: `w`
last	Show listing of last logged in users. Example: `last`
id	Display user and group information. Example: `id username`
Process Management
ps	View active processes. Examples: `ps` - Your processes `ps aux` - All processes `ps -ef` - All processes (alternative format)
top	Real-time task manager. Example: `top` Press 'q' to quit, 'k' to kill a process, 'r' to renice.
htop	Interactive process viewer (must be installed). Example: `htop`
kill	Terminate process by PID. Examples: `kill PID` `kill -9 PID` - Force kill `kill -l` - List signal names
killall	Terminate process by name. Examples: `killall processname` `killall -9 processname` - Force kill
pkill	Kill processes by name or other attributes. Examples: `pkill processname` `pkill -u username` - Kill all processes by user
bg	Send process to background. Example: `bg %1`
fg	Bring process to foreground. Example: `fg %1`
jobs	List background jobs. Example: `jobs`
nice	Run process with modified priority. Example: `nice -n 10 command` - Lower priority (higher nice value)
Networking
ip	Show/manipulate routing, devices, policy routing. Examples: `ip addr` - Show IP addresses `ip link` - Show network interfaces `ip route` - Show routing table
ifconfig	Network interfaces (older systems). Example: `ifconfig` Deprecated in favor of `ip` command on newer systems.
ping	Send ICMP ECHO_REQUEST to network hosts. Examples: `ping google.com` `ping -c 4 192.168.1.1` - Send 4 packets only
netstat	Network statistics. Examples: `netstat -tuln` - Show listening TCP/UDP ports `netstat -anp` - Show all connections with PIDs
ss	Socket statistics (modern replacement for netstat). Examples: `ss -tuln` - Show listening ports `ss -s` - Show summary
traceroute	Print the route packets take to network host. Example: `traceroute google.com`
dig	DNS lookup utility. Examples: `dig example.com` `dig example.com MX` - Query MX records
nslookup	Query Internet name servers interactively. Example: `nslookup example.com`
wget
curl	Transfer data from or to a server.
Security
sudo	Execute command as another user (usually root). Examples: `sudo command` `sudo -u username command` - As specific user
ufw	Uncomplicated Firewall management. Examples: `sudo ufw status` `sudo ufw allow 22` - Allow SSH `sudo ufw enable` - Enable firewall
ssh	OpenSSH SSH client (remote login). Examples: `ssh user@hostname` `ssh -p 2222 user@hostname` - Connect to custom port
lastlog	Show last login of users. Example: `lastlog`
chroot	Run command with special root directory. Example: `sudo chroot /newroot /bin/bash`
su	Switch user. Examples: `su username` `su -` - Switch to root with environment
visudo	Edit the sudoers file safely. Example: `sudo visudo`
passwd	Change user password. Examples: `passwd` - Change your password `sudo passwd username` - Change another user's password
fail2ban-client	Ban IPs making too many failed login attempts. Examples: `sudo fail2ban-client status` `sudo fail2ban-client set sshd unbanip 192.168.1.1`
nmap	Network exploration tool and security scanner. Examples: `nmap 192.168.1.1` `nmap -sV -O 192.168.1.1` - Version and OS detection
Archives & Compression
tar	Tape archive utility (create/extract archives). Examples: `tar -cvf archive.tar directory/` - Create archive `tar -xvf archive.tar` - Extract archive `tar -czvf archive.tar.gz directory/` - Create compressed archive
zip	Package and compress files. Example: `zip -r archive.zip directory/`
unzip	Extract files from ZIP archives. Example: `unzip archive.zip`
gzip	Compress files. Examples: `gzip file.txt` - Compress file `gzip -d file.txt.gz` - Decompress file
gunzip	Decompress files compressed by gzip. Example: `gunzip file.gz`
bzip2	Compress files using Burrows-Wheeler algorithm. Example: `bzip2 file.txt`
xz	Compress files with LZMA algorithm. Example: `xz file.txt`
7z	High compression ratio file archiver. Examples: `7z a archive.7z directory/` - Create archive `7z x archive.7z` - Extract archive
rar	Create and extract RAR archives. Examples: `rar a archive.rar directory/` `rar x archive.rar`
zcat	View compressed files without decompressing. Example: `zcat file.gz`
Permissions & Ownership
chmod	Change file permissions. Examples: `chmod 755 file.txt` - Set permissions using octal `chmod +x script.sh` - Add execute permission `chmod -R 750 directory/` - Recursive change Permissions: 4 (read), 2 (write), 1 (execute). Common: 755 (rwxr-xr-x), 644 (rw-r--r--)
chown	Change file owner and group. Examples: `chown user:group file.txt` `chown -R user:group directory/` - Recursive change
chgrp	Change group ownership. Example: `chgrp groupname file.txt`
umask	Set default file permissions. Example: `umask 022`
getfacl	Get file access control lists. Example: `getfacl file.txt`
setfacl	Set file access control lists. Examples: `setfacl -m u:username:rwx file.txt` `setfacl -x u:username file.txt` - Remove ACL entry
Text Processing
awk	Pattern scanning and processing language. Examples:
sed	Stream editor for filtering and transforming text. Examples: `sed 's/old/new/g' file.txt` - Replace text `sed -i 's/old/new/g' file.txt` - In-place edit
cut	Remove sections from each line of files. Examples:
sort	Sort lines of text files. Examples: `sort file.txt` `sort -r file.txt` - Reverse sort
uniq	Report or omit repeated lines. Examples: `uniq file.txt` `sort file.txt \| uniq -c` - Count occurrences
tr	Translate or delete characters. Examples: `tr 'a-z' 'A-Z' < file.txt` - Convert to uppercase `echo "hello" \| tr -d 'l'` - Delete characters
tee	Read from standard input and write to standard output and files. Example: `command \| tee output.txt`
column	Format input into multiple columns. Example: `ls -l \| column -t`
nl	Number lines of files. Example: `nl file.txt`
fold	Wrap each input line to fit in specified width. Example: `fold -w 80 file.txt`