Linux Commands

File Commands:

• ls: List directory contents.
• ls -al: Formatted listing with hidden files.
• cd dir: Change directory to dir.
• cd: Change to home directory.
• pwd: Show current directory.
• mkdir dir: Create a directory named dir.
• rm file: Delete a file.
• rm -r dir: Delete a directory (recursively).
• rm -f file: Force remove a file.
• rm -rf dir: Force remove a directory (be cautious with this command).
• cp file1 file2: Copy file1 to file2.
• cp -r dir1 dir2: Copy dir1 to dir2; create dir2 if it doesn't exist.
• mv file1 file2: Rename or move file1 to file2. If file2 is an existing directory, moves file1 into directory file2.
• ln -s file link: Create a symbolic link (shortcut) named link to file.
• touch file: Create or update a file.
• cat > file: Place standard input into file.
• more file: Output the contents of a file.
• head file: Output the first 10 lines of a file.
• tail file: Output the last 10 lines of a file.
• tail -f file: Output the contents of a file as it grows, starting with the last 10 lines.

Process Management:

• ps: Display your currently active processes.
• top: Display all running processes.
• kill pid: Kill a process with process ID pid.
• killall proc: Kill all processes with the name proc.
• bg: List stopped or background jobs; resume a stopped job in the background.
• fg: Bring the most recent job to the foreground.
• fg n: Bring job n to the foreground.

File Permissions:

• chmod octal file: Change the permissions of a file to octal (numeric representation), specifying read (4), write (2), and execute (1) permissions for user, group, and world.
  • Examples:
    • chmod 777 file: Read, write, and execute for all.
    • chmod 755 file: Rwx for owner, rx for group and world.

SSH:

• ssh user@host: Connect to a host as a user.
• ssh -p port user@host: Connect to a host on a specific port as a user.
• ssh-copy-id user@host: Add your SSH key to a host for a user to enable a passwordless login.

Searching:

• grep pattern files: Search for a pattern in files.
• grep -r pattern dir: Search recursively for a pattern in a directory.
• command | grep pattern: Search for a pattern in the output of a command.
• locate file: Find all instances of a file.

System Info:

• date: Show the current date and time.
• cal: Show this month's calendar.
• uptime: Show current uptime.
• w: Display who is online.
• whoami: Display the currently logged-in user.
• finger user: Display information about a user.
• uname -a: Show kernel information.
• cat /proc/cpuinfo: Display CPU information.
• cat /proc/meminfo: Display memory information.
• man command: Show the manual for a command.
• df: Show disk usage.
• du: Show directory space usage.
• free: Show memory and swap usage.
• whereis app: Show possible locations of an app.
• which app: Show which app will be run by default.

Compression:

• tar cf file.tar files: Create a tar file named file.tar containing specified files.
• tar xf file.tar: Extract the files from a tar file.
• tar czf file.tar.gz files: Create a tar file with Gzip compression.
• tar xzf file.tar.gz: Extract a tar file using Gzip.
• tar cjf file.tar.bz2: Create a tar file with Bzip2 compression.
• tar xjf file.tar.bz2: Extract a tar file using Bzip2.
• gzip file: Compress a file and rename it to file.gz.
• gzip -d file.gz: Decompress a file.gz back to the original file.

Network:

• ping host: Ping a host and output results.
• whois domain: Get whois information for a domain.
• dig domain: Get DNS information for a domain.
• dig -x host: Reverse lookup for a host.
• wget file: Download a file.
• wget -c file: Continue a stopped download.

Installation:

• dpkg -i pkg.deb: Install a Debian package.
• rpm -Uvh pkg.rpm: Install an RPM package.

Install from Source:

1. ./configure
2. make
3. make install

Shortcuts:

• Ctrl+C: Halt the current command.
• Ctrl+Z: Stop the current command; resume with fg in the foreground or bg in the background.
• Ctrl+D: Log out of the current session (similar to exit).
• Ctrl+W: Erase one word in the current line.
• Ctrl+U: Erase the whole line.
• Ctrl+R: Type to bring up a recent command.
• !!: Repeat the last command.
• exit: Log out of the current session.