Linux Basics
$ pwd -> prints current path$ ls -> prints non-hidden directory contents$ ls -l -> prints non-hidden directory contents + more info$ cd <dir name> -> changes current directory to <dir name>$ cd .. -> changes current directory to one directory higher$ cd ~ -> changes current directory to home directory
$ ls -a -> prints non-hidden and hidden directory contents$ ls -la -> prints non-hidden and hidden directory contents + more info
$ mkdir <dir name> -> creates directory <dir name>$ touch <file name> -> creates file <file name>$ mv <file name> <new path> -> moves file <file name> into <new path>$ mv <file name> <new file name> -> renames file <file name> to <new file name>$ cp <file name> <copy name> -> copies <file name> into <copy name> (same contents, 2 files now)$ cp -r <dir name> <copy name> -> copies directory <dir name> and its contents into <copy name>$ rm <file name> -> deletes <file name>$ rm -r <dir name> -> deletes directory <dir name> and its contents$ rmdir <dir name> -> deletes empty directory <dir name>
$ cat <file> -> prints entire contents of <file>$ less <file> -> opens <file> in scrollable pager (arrow keys, q to quit)$ head <file> -> prints first 10 lines of <file>$ head -n <num> <file> -> prints first <num> lines of <file>$ tail <file> -> prints last 10 lines of <file>$ tail -n <num> <file> -> prints last <num> lines of <file>$ tail -f <file> -> prints and follows changes in <file> in real time
$ find <path> -name <pattern> -> searches <path> for files matching <pattern>$ find <path> -type f -> lists all files in <path>$ find <path> -type d -> lists all directories in <path>$ locate <filename> -> quickly finds paths containing <filename>$ grep <pattern> <file> -> prints lines in <file> containing <pattern>$ grep -r <pattern> <dir> -> searches all files in <dir> for <pattern>$ grep -i <pattern> <file> -> searches <file> ignoring case$ which <command> -> shows path of <command> if installed$ whereis <command> -> shows all locations of <command> (binary, source, man page)
$ ls -l -> shows permissions, owner, group, and file info$ chmod <mode> <file> -> changes file permissions (e.g., 755 or +x)$ chown <user>:<group> <file> -> changes ownership of file$ groups -> shows groups the current user belongs to$ umask -> shows default permission mask for new files
$ whoami -> prints current logged-in user$ id -> shows user ID, group ID, and memberships$ su <user> -> switch to another user account$ sudo <command> -> run command with root privileges$ adduser <username> -> create new user$ cat /etc/passwd -> shows user account info
$ ps -> shows running processes for current shell$ ps aux -> shows all running processes with details$ top -> real-time interactive process monitor$ htop -> user-friendly interactive process monitor$ kill <PID> -> kills process with given PID$ jobs -> lists background jobs in shell<command> & -> runs command in background$ fg %<job> -> brings background job to foreground$ bg %<job> -> resumes job in background
$ uname -a -> prints kernel name, version, machine, and system info$ hostname -> prints the system’s hostname$ uptime -> shows system uptime, logged-in users, and load averages$ df -h -> shows disk space usage (human-readable)$ free -m -> shows memory usage in MB
$ ifconfig -> shows network interfaces and IP addresses (legacy)$ ip a -> shows network interfaces and IP addresses (modern)$ ping <host> -> tests connectivity to <host>$ netstat -tuln -> shows active connections and listening ports (deprecated)$ ss -tuln -> shows active connections and listening ports (modern)$ curl <url> -> fetches and displays contents from <url>$ wget <url> -> downloads file(s) from <url>
$ tar -cvf <archive.tar> <files> -> create tar archive$ tar -xvf <archive.tar> -> extract tar archive$ tar -czvf <archive.tar.gz> <files> -> create compressed tar.gz archive$ tar -xzvf <archive.tar.gz> -> extract tar.gz archive$ gzip <file> -> compress file into .gz$ gunzip <file.gz> -> decompress .gz file$ zip <archive.zip> <files> -> create zip archive$ unzip <archive.zip> -> extract zip archive
$ nano <file> -> open file in nano editor$ vim <file> -> open file in vim editor$ gedit <file> -> open file in gedit GUI editor
#!/bin/bash -> shebang to define shell for script$ nano <script.sh> -> create/edit script file$ chmod +x <script.sh> -> make script executable$ ./<script.sh> -> run script
$ echo $PATH -> prints PATH variable$ export <VAR>=<value> -> sets environment variable for session$ echo $VAR -> prints value of variable$ nano ~/.bashrc -> edit bashrc to make variables permanent
$ ln -s <target> <link> -> create symbolic link to target$ ls -l -> shows symlinks and their targets$ cat <symlink> -> follows symlink and prints target contents
$ sudo apt update -> update package list$ sudo apt upgrade -> upgrade installed packages$ sudo apt install <pkg> -> install package$ sudo apt remove <pkg> -> remove package$ dpkg -i <file.deb> -> install from local .deb file$ apt-cache search <term> -> search package repositories
/var/log/ -> main system log directory$ cat /var/log/auth.log -> view authentication logs$ tail -f /var/log/syslog -> follow system log in real time$ dmesg -> view kernel messages
> <file> -> overwrite file with command output>> <file> -> append command output to file< <file> -> use file as input to command<cmd1> | <cmd2> -> pipe output of cmd1 into cmd2
* -> matches zero or more characters? -> matches exactly one character[abc] -> matches one character in set
$ crontab -l -> list cron jobs$ crontab -e -> edit cron jobs0 0 * * * <cmd> -> run command every day at midnight$ systemctl status cron -> check cron service
$ ssh user@host -> connect to host as user$ ssh -p <port> user@host -> connect with custom port$ ssh -i <key> user@host -> connect with SSH key$ scp <file> user@host:/path> -> copy file to remote host
$ systemctl status <service> -> check service status$ systemctl start <service> -> start service$ systemctl stop <service> -> stop service$ systemctl enable <service> -> enable service at boot$ service <service> restart -> restart service (legacy)