Linux Command Line

Navigate Directories

Linux File System Tree:

• bin: binary (commands and utilities that all users can run)
• sbin: this directory contains programs that performs vital system tasks (network management, disk partitioning). Only the superuser has access to these programs.
• home: each user is given a directory under the home directory. A user can store anything in his home directory
• opt: optional (additional software)
• tmp: temporary files, files created by various programs
• var: variable data, data that frequently changes over time.

Linux Commands In One Place

• Navigation Commands
• Files and Directories
• Text File Manipulation Commands
• System Information Commands
• User and Permission Management Commands
• Networking Commands

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Navigation Commands

• pwd: Display the current working directory.

  • Example:

    $ pwd
    /home/john

• ls: List files and directories in the current directory.

  • Example:

    $ ls
    Desktop  Documents  Downloads  Music  Pictures  Videos

• ls -l: Display file/directory information in long format.

  • Example:

    $ ls -l
    total 4
    drwxr-xr-x 2 john john 4096 Jul  9 23:35 Desktop

• ls -a: Display all files/directories, including hidden ones.

  • Example:

    $ ls -a
    .  ..  .bashrc  .profile  Desktop  Documents  Downloads

• cd: Change directory.

  • cd [directory_name]: Move to the specified directory.
    • Example:

      $ cd Documents

  • cd ..: Move to the parent directory.
    • Example:

      $ cd ..

  • cd ~: Move to the user’s home directory.
    • Example:

      $ cd ~

• mkdir: Create a new directory.

  • mkdir [directory_name]: Create a directory with a specific name.
    • Example:

      $ mkdir new_directory

Files and Directories

• touch [file_name]: Create an empty file with a specific name.

  • Example:

    $ touch newfile.txt

• cp [source] [destination]: Copy source to destination.

  • Example:

    $ cp file1.txt /home/john/Documents/

• mv [source] [destination]: Move source to destination.

  • Example:

    $ mv file1.txt /home/john/Documents/

  • mv [old_name] [new_name]: Rename a file/directory.
    • Example:

      $ mv oldname.txt newname.txt

• rm [file_name]: Delete a file with a specific name.

  • Example:

    $ rm file1.txt

  • rm -r [directory_name]: Delete a directory and its contents recursively.
    • Example:

      $ rm -r old_directory

• cat [file_name]: Display the contents of a specific file.

  • Example:

    $ cat file1.txt
    This is the content of the file.

Text File Manipulation Commands

• nano or vim: Edit text files in the terminal.

  • Example:

    $ nano file1.txt

• echo [text]: Display text in the terminal.

  • Example:

    $ echo "Hello, World!"
    Hello, World!

  • echo [text] > [file_name]: Save text to a file (overwrite content).
    • Example:

      $ echo "Hello, World!" > file1.txt

  • echo [text] >> [file_name]: Append text to a file (without overwriting).
    • Example:

      $ echo "Hello, again!" >> file1.txt

System Information Commands

• uname: Display information about the system.

  • Example:

    $ uname
    Linux

  • uname -a: Display detailed system information.
    • Example:

      $ uname -a
      Linux myhostname 5.4.0-42-generic #46-Ubuntu SMP Fri Jul 10 00:24:02 UTC 2020 x86_64 x86_64 x86_64 GNU/Linux

• top: Display a list of running processes.

  • Example:

    $ top
    top - 23:35:01 up  2:29,  1 user,  load average: 0.72, 1.07, 1.04
    Tasks: 174 total,   1 running, 173 sleeping,   0 stopped,   0 zombie
    %Cpu(s):  2.2 us,  0.7 sy,  0.0 ni, 96.8 id,  0.2 wa,  0.0 hi,  0.1 si,  0.0 st
    KiB Mem :  4048172 total,  1512344 free,  1385300 used,  1150528 buff/cache
    KiB Swap:  2097148 total,  2097148 free,        0 used.  2308296 avail Mem 

• free: Display memory usage.

  • Example:

    $ free
                  total        used        free      shared  buff/cache   available
    Mem:        4048172     1512344     1385300       12324     1150528     2308296
    Swap:       2097148           0     2097148

• df: Display disk space usage information.

  • Example:

    $ df
    Filesystem     1K-blocks     Used Available Use% Mounted on
    udev             1998172        0   1998172   0% /dev
    tmpfs             404128     1272    402856   1% /run
    /dev/sda1       30458336 15129504  13853072  53% /

User and Permission Management Commands

• sudo: Execute commands as a superuser (root).

  • Example:

    $ sudo apt update

• useradd: Add a new user.

  • Example:

    $ sudo useradd newuser

• passwd: Change a user’s password.

  • Example:

    $ sudo passwd newuser

• chmod: Change file/directory permissions.

  • Example:

    $ chmod 755 script.sh

• chown: Change file/directory ownership.

  • Example:

    $ sudo chown john:john file1.txt

Networking Commands

• ping [ip_address]: Send ICMP echo packets to a network address.

  • Example:

    $ ping google.com

• ifconfig or ip: Display network interface information.

  • Example:

    $ ifconfig

  • Example:

    $ ip a

• ssh [username]@[ip_address]: Connect to a remote machine using Secure Shell (SSH).

  • Example:

    $ ssh john@192.168.1.1

General Commands

• w: Display information about currently logged in users and what each user is doing.

  • Example:

    $ w
    23:35:01 up  2:29,  1 user,  load average: 0.72, 1.07, 1.04
    USER     TTY      FROM             LOGIN@   IDLE   JCPU   PCPU WHAT
    john     :1       :1               21:04   ?xdm?  34:58   0.01s /usr/lib

• whoami: Display the current logged in user's username.

  • Example:

    $ whoami
    john

• groups: Display the groups the user belongs to.

  • Example:

    $ groups
    john adm cdrom sudo dip plugdev lpadmin sambashare

• id: Display user and group information.

  • Example:

    $ id
    uid=1000(john) gid=1000(john) groups=1000(john),4(adm),24(cdrom),27(sudo),30(dip),46(plugdev),116(lpadmin),126(sambashare)

• hostname: Display the system's hostname.

  • Example:

    $ hostname
    myhostname

• date: Display or set the system date and time.

  • Example:

    $ date
    Tue Jul  9 23:35:01 UTC 2024

• uptime: Display the system uptime.

  • Example:

    $ uptime
    23:35:01 up  2:29,  1 user,  load average: 0.72, 1.07, 1.04

• uname -a: Display detailed system information.

  • Example:

    $ uname -a
    Linux myhostname 5.4.0-42-generic #46-Ubuntu SMP Fri Jul 10 00:24:02 UTC 2020 x86_64 x86_64 x86_64 GNU/Linux

• df: Display disk space usage information.

  • Example:

    $ df
    Filesystem     1K-blocks     Used Available Use% Mounted on
    udev             1998172        0   1998172   0% /dev
    tmpfs             404128     1272    402856   1% /run
    /dev/sda1       30458336 15129504  13853072  53% /

• du: Display disk usage of files and directories.

  • Example:

    $ du -h
    4.0K    ./Desktop
    1.6G    ./Downloads
    2.1G    ./Documents

• free: Display memory usage.

  • Example:

    $ free
                  total        used        free      shared  buff/cache   available
    Mem:        4048172     1512344     1385300       12324     1150528     2308296
    Swap:       2097148           0     2097148

• top: Display a list of running processes.

  • Example:

    $ top
    top - 23:35:01 up  2:29,  1 user,  load average: 0.72, 1.07, 1.04
    Tasks: 174 total,   1 running, 173 sleeping,   0 stopped,   0 zombie
    %Cpu(s):  2.2 us,  0.7 sy,  0.0 ni, 96.8 id,  0.2 wa,  0.0 hi,  0.1 si,  0.0 st
    KiB Mem :  4048172 total,  1512344 free,  1385300 used,  1150528 buff/cache
    KiB Swap:  2097148 total,  2097148 free,        0 used.  2308296 avail Mem 

• ps: Display currently running processes.

  • Example:

    $ ps
      PID TTY          TIME CMD
    21549 pts/0    00:00:00 bash
    21879 pts/0    00:00:00 ps

• kill [pid]: Terminate a process by its PID.

  • Example:

    $ kill 1234

• history: Display the command history.

  • Example:

    $ history
        1  ls
        2  cd ..
        3  pwd