Day 2: Mastering The Linux Basic Commands Part 2

Adrian Rubico

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Aug 5, 2024

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01:18 AM GMT+8

As we continue mastering the basic Linux commands, this blog will cover System Information and Processes, Permissions and Ownership, and Basic Networking.

System Information and Processes

  1. top command
    Displays real-time system processes and resource usage.
bash 
top
  1. ps command (Process Statuses)
    Lists currently running processes. Use ps aux | grep process for specific process detailed view.
bash 
ps
ps aux
ps aux | grep python
  1. kill command
    Terminates a process by its ID (PID). Use kill -9 for a forceful termination.
bash 
kill PID
  1. df command (Disk Free)
    Shows disk space usage. Use df -h for a human-readable format.
bash 
df
df -h
  1. free command
    Displays memory usage, with free -h providing a human-readable format.
bash 
free
free -h

Permissions and Ownership

  1. chmod command (Change Mode)
    Modifies file or directory permissions. Here's how to read and understand these permissions as given in this example -rwxr-xr--

    This string is divided into four parts:
    File Type Indicator (- or d or l):
    The first character represents the type of file:
    - : Regular file
    d : Directory
    l : Symbolic link

    User (Owner) Permissions (rwx):
    The next three characters represent the permissions for the user who owns the file:
    r : Read permission (4)
    w : Write permission (2)
    x : Execute permission (1)
    Example: rwx means the user has read, write, and execute permissions.

    Group Permissions (r-x):
    The following three characters represent the permissions for the group that owns the file:
    r : Read permission (4)
    - : No write permission (0)
    x : Execute permission (1)
    Example: r-x means the group has read and execute permissions, but no write permission.

    Other (World) Permissions (r--):
    The final three characters represent the permissions for all other users:
    r : Read permission (4)
    - : No write permission (0)
    - : No execute permission (0)
    Example: r-- means others have read-only permission.

    Here's a detailed table explaining the chmod command and the permissions it sets for files and directories in Linux:

SymbolNumerical ValuePermission
---0No Permission
--x1Execute
-w-2Write
-wx3Write & Execute
r--4Read
r-x5Read & Execute
rw-6Read & Write
rwx7Full Permission
bash 
# Chown Permissions
chmod 777 filename           #Full Permissions for User, Group, and Others (777)
chmod 644 filename           #Read and Write for User, Read Only for Group and Others (644)
chmod 750 filename           #No Permissions for Others (750)
chmod u+x filename           #Add execute permission for the user
chmod o+x filename           #Remove write permission for others
chmod u=rw,g=r,o=r filename  #Set read and write for user, and read for group and others
  1. chown command (Change Ownership)
    Changes file or directory owner and group.
bash 
chown user:group directory/file    
chown -R user:group directory/file   #operate on files and directories recursively.

Networking

  1. ping command
    Tests connectivity to a network host.
bash 
ping example.com
  1. ifconfig command
    Displays network interface information.
bash 
ifconfig
  1. curl command
    Transfers data from or to a server using supported protocols (HTTP, FTP, etc.). More details on how to use curl are on this blog site curl-command-in-linux.
bash 
curl -I http://example.com    #Fetch the HTTP-header only!

💡 Checking out this website explainshell is very helpful if you want to learn more about command-line usage, including arguments.

Wrap-up

This guide provides an overview of essential concepts and commands in the Linux system. Understanding these fundamentals is crucial in the world of DevOps. In the next blog, we will explore how the Linux environment can be utilized to automate processes through bash/shell scripting.

TAGS:

#90DaysDevOpsChallenge linux

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