The article begins with the basics, introducing fundamental commands for navigating the file system, managing files and directories, and working with processes. It then progresses to more advanced commands that enhance your Linux skills and enable you to perform complex tasks efficiently.
This article aims to share valuable knowledge with the community. By reading and applying the concepts discussed, readers will become more proficient in using Linux commands and be equipped to handle a variety of tasks confidently.
Whether you're a student, professional, or simply interested in Linux, Mastering Common Linux Commands: From Beginner to Pro is an excellent resource to enhance your Linux skills and empower you to make the most of this versatile operating system.
Most Common command used :
| uname -a | Display Linux system information |
| whoami | Who you are logged in as |
| uname -r | Display kernel release information |
| uptime | Show how long the system has been running + load |
| hostname | Show system host name |
| last reboot | Show system reboot history |
| date | Show the current date and time |
| cal | Show this month's calendar |
| w | Display who is online |
| free -h | Display free and used memory ( -h for human readable, -m for MB, -g for GB.) |
| top | Display and manage the top processes |
| watch df -h | Execute "df -h", showing periodic updates |
| last | Display the last users who have logged onto the system. |
| who | Show who is logged into the system. |
| useradd -c "John Smith" -m john | Create an account named john, with a comment of "John Smith" and create the user's home directory. |
| userdel john | Delete the john account. |
| usermod -aG sales john | Add the john account to the sales group |
| ls -al | List all files in a long listing (detailed) format |
| pwd | Display the present working directory |
| mkdir directory | Create a directory |
| rm file | Remove (delete) file |
| rm -r directory | Remove the directory and its contents recursively |
| rm -f file | Force removal of file without prompting for confirmation |
| rm -rf directory | Forcefully remove directory recursively |
| cp file1 file2 | Copy file1 to file2 |
| cp -r source_directory destination | Copy source_directory recursively to destination. If destination exists, copy source_directory into destination, otherwise create destination with the contents of source_directory. |
| mv file1 file2 | Rename or move file1 to file2. If file2 is an existing directory, move file1 into directory file2 |
| touch file | Create an empty file or update the access and modification times of file. |
| cat file | View the contents of file |
| head file | Display the first 10 lines of file |
| tail file | Display the last 10 lines of file |
| ps | Display your currently running processes |
| grep pattern file | Search for pattern in file |
| df | Display disk usage. |
| df -h | Show free and used space on mounted filesystems |
| df -H | Display disk usage in gigabytes, megabytes, or kilobytes. |
| rm -r * | Delete every file and every directory. |
| kill | Terminate processes without having to log out or reboot. |
| login | Create a new session on the system. |
| lsof | List open files. |
| cal -y | Prints current year's calendar. |
| sudo su root1 | Switch to user "root1". |
| useradd "root1" | Creates a user "root1". |
| passwd "root1" | Assign password to user "root1". |
| logname | Display the login name of the current user. |
| mkdir myfiles files | Create two directories (myfiles, files). |
| diff 1.txt 2.txt | Compare the contents of two files (1.txt, 2.txt). |
| wc 1.txt | Tells you how many lines, words, and characters there are in a file (1.txt). |
| cp 1.txt 0.txt | Replace the contents of 0.txt with that of 1.txt. |
| mv 1.txt 0.txt | Rename a file named 1.txt to 0.txt. |
| echo 'Hello World' > myfiles.txt | Create a file (myfiles.txt) containing a text (Hello World). |
Last blog, we learn some basic Linux commands and their uses. Today we will learn more about command and their uses. So, let's learn about basic and some advanced Linux command.
To view what's written in a file.
Cat is a command through which you can review what's written in a file.
For creating Linux Files we used different commands like
cat command: to view what is written in the file we used the cat command
vim command
touch command
nano command
File Systems Permissions and Ownership
File System Hierarchy:
Linux follows a hierarchical file system structure, starting from the root directory / and branching into various directories:
Root Directory (/): The top-level directory containing all other directories and files.
/bin, /sbin, /usr, /etc: Directories holding essential binaries, system binaries, user binaries, and system configuration files, respectively.
/home: Houses user home directories.
/var: Contains variable files like logs, databases, mail, and more.
/tmp: Used for temporary files.
/opt: Optional software applications often reside here.
/dev: Device files for hardware components.
/proc: Virtual file system that provides access to kernel and process information.
File Permissions and Ownership:
Linux file permissions are categorized into three levels: owner, group, and others. These permissions are represented by read (r), write (w), and execute (x).
Types of Permissions:
Read (
r): Allows reading and viewing the contents of a file or directory.Write (
w): Permits modifying, appending, or deleting a file's contents, and creating or deleting files within a directory.Execute (
x): Grants the ability to execute files or traverse through directories.
Let's use an example to illustrate this:
To change the access permissions of files
Chmod is the command used to change the access permissions of a file.
chmod
Example:
rwx rwx rwx
In that values are r=4,w=2,x=1 so 4+2+1=7 then total value is 777
chmod 777 permission says all permission are given like we read, write and execute
chmod 777 test-file.txt
The command chmod 777 test-file sets the access permissions of the file test-file to read, write, and execute for the owner, group, and others.
chmod 600 filename
To give read and write permissions to the owner, and no permissions to group and others
chmod 750 filename
To give full permissions (read, write, and execute) to the owner, and read and execute permissions to the group, and no permissions to others
chmod 700 filename
To give full permissions (read, write, and execute) to the owner, and no permissions to the group and others:
chmod 444 filename
To give only read permissions to the owner, group, and others. not write and execute permissions to owner, group and others.
or you can simply says: to remove write and execute permissions from the owner, group, and others
This permission setting is commonly used when you want to make a file read-only for everyone, preventing any modifications or execution.
Now, let start deeply discuss file access permission.
chmod 755 filename
To give read, write, and execute permissions to the owner, and read, execute permission to group and others
Let's break down the permission code:
The leftmost digit,
7, represents the permission for the owner of the file.The middle digit,
5, represents the permission for the group that the file belongs to.The rightmost digit,
5, represents the permission for other users (not the owner or group).
Each digit in the permission code represents a combination of read (4), write (2), and execute (1) permissions.
Here's a breakdown of the permission codes:
7: This grants the owner of the file full permissions, which include read, write, and execute.5: This grants the group read and execute permissions, but not write permissions.5: This grants other users read and execute permissions, but not write permissions.
In summary, executing chmod 755 filename sets the file permissions as follows:
The owner of the file has full control (read, write, and execute).
The group has read and execute permissions.
Other users have read and execute permissions.
This permission setting is commonly used for executable files or scripts that should be readable and executable by all users, but not writable to maintain security.
Chown Command file Permissions:
chown Command:
chown stands for "change owner" and is used to change the owner of a file or directory.
sudo chown new_owner filename
new_owner: The new user or user ID to assign as the owner.file(s): The file or list of files/directories to which ownership will be changed.
Example:
Let's assume you want to change the owner of a file named test-file.txt to a user named niloy [ my younger brother name ]:
sudo chown niloy test-file.txt
Here, after executing the "ls -l" command, we noticed that the owner of our test-file.txt is 'ubuntu,' right?
Now, let's change the file owner from the 'ubuntu' user to a new user named 'niloy' and grant permission.
Let's attempt to implement this.
sudo chown niloy test-file.txt
After executing this command, we see an error message stating "invalid user" because we don't have any user named 'niloy.' So, first, let's create a user named 'niloy,' and then let's try again to see if we can change the file's owner.
After creating the user, when we execute the same command, we can observe that the file's owner name has indeed been changed.
chgrp group Ownership file Permissions :
chgrp Command:
chgrp stands for "change group" and is used to change the group ownership of a file or directory.
chgrp new_group filename
new_group: The new group or group ID to assign as the group owner.file(s): The file or list of files/directories to which group ownership will be changed.
Example:
Changing the group ownership of the test-file.txt file to newgroup:
chgrp newgroup test-file.txt
Here, after executing the "ls -l" command, we noticed that the group of our test-file.txt is 'ubuntu,' right?
Now, let's change the file group from the 'ubuntu' user to a new user named 'niloy' and grant permission.
Let's attempt to implement this.
We had created a new user named 'niloy' earlier to change the file's owner, right?
We know that when creating any user, a default group with the same name is automatically created for that user.
To verify this, we executed the following command.
id niloy
After executing it, we observed that 'niloy' indeed has a default group.
So now, we will change the group ownership of our file to a new group named 'niloy' using the command below.
sudo chgrp niloy test-file.txt
Now, after running the 'ls -l' command again, we can see that the group owner of our file 'test-file.txt' has changed.
Permissions and Use Cases:
File Ownership Change: Use
chownwhen you want to change both the user and group ownership of a file or directory.Group Ownership Change: Use
chgrpwhen you only want to modify the group ownership without altering the user owner.
These commands are typically used by system administrators to manage file and directory ownership, especially when users need access to specific files or when group permissions require modification for collaboration purposes. Proper ownership and group assignments are critical for effective access control and data security in Linux systems.
Access Control Lists (ACLs)
Access Control Lists (ACLs) in Linux are an extension of the standard file permission system, allowing for more granular control over access to files and directories. ACLs enable you to define permissions for specific users or groups beyond the traditional owner, group, and others classifications. They provide a finer level of access control and are useful in multi-user environments or when more complex permission settings are required.
Usage of ACLs:
Viewing ACLs:
To view ACLs for a file or directory, use the getfacl command:
$getfacl filename
We've previously applied file permissions to the file named 'test-file'.
Now, we'll use the 'getfacl' command to check the permissions of this file. This command will display the file name, the file's user owner, group owner, and the permissions represented by 'read' (r), 'write' (w), and 'execute' (x) for three categories: owner, group, and others.
For example---
getfacl test-file.txt
file: test-file.txt
owner: niloy
group: niloy
user::rwx
group::rwx
other::rwx
After executing the command "getfacl test-file.txt," we noticed in the terminal that the command "getfacl" wasn't found but suggested to be installed with: "sudo apt install acl."
Since we need the 'acl' command to check permissions, we must install 'acl' first. Therefore, let's execute the following command:
sudo apt install acl
Now, we'll execute the command "getfacl test-file.txt" again to check the information related to the "test-file.txt" file.
Once executed, it will display all the information about the file, including its name, owner's name, group's name, and permission categories for users, groups, and others.
For a clearer understanding of ACL permissions, let's create a new file named "nahid-test-file.txt."
Now, to view the access control list of this file, we'll execute the command 'getfacl nahid-test-file.txt.'
getfacl nahid-test-file.txt
After execution, we see that the owner and group name of this file are 'ubuntu' because, by default, we're working in the 'ubuntu' environment. Also, observing the permissions of this file, we find that both the owner and group have read and write permissions, while others have only read permissions.
Setting ACLs:
setfacl command
The setfacl command is used to set or modify ACLs for files and directories:
If we want to modify our file's permissions easily, we'll use the "setfacl" command:
setfacl -m u:username:permissions filename
Let's add a new user for our file and grant full permissions to that user using the "setfacl" command.
For instance, we'll assign a new user named "nahid" for our file and grant full permissions to that user.
sudo setfacl -m u:nahid:rwx nahid-test-file.txt
The issue here is that we haven't created a user named "nahid" yet, so I've faced this problem. Thus, I'll create the "nahid" user now.
After executing the command, we can see that the new user named "nahid" has been given "rwx" full permissions.
Removing ACL Entry:
Remove an ACL entry for a user on a file:
setfacl -x u:username filename
Now, if we want to remove the "nahid" user specifically for this file, we'll use the following command:
sudo setfacl -x u:nahid nahid-test-file.txt
After executing the removal command, we can observe that the user list for this specific file no longer shows any user named "nahid," meaning that there are no permissions for the "nahid" user for this file.
ACLs provide a powerful means of managing access control in Linux, allowing administrators to define fine-grained permissions for users and groups. They are particularly useful in scenarios where more detailed access control is required beyond the scope of standard permissions. However, they should be used thoughtfully and documented carefully to maintain system security and integrity.
Histroy:
To check which commands you have run till now.
history command is used to check the commands you have run till now.
histroy
To remove a directory/ Folder.
To remove a directory, we use the “rm” command. We use “rm -r” if the directory is non-empty.
Some common options that you can use with the rm command are:
-f: Force removal of files without prompting for confirmation.
-r: Recursively remove directories and their contents.
The rmdir command in Linux is used to remove empty directories from the file system.
rm -rf It is used to forcefully and recursively remove files and directories from the file system, including non-empty directories.
rm-rp = Remove non-empty directory including parent and subdirectory
rm-r = Removes empty directories
To create a fruits.txt file and view the content.
Add content in devops.txt (One in each line) - Apple, Mango, Banana, Cherry, Kiwi, Orange, Guava.
To Show only the top three fruits from the file.
To show only the top three fruits we will use the head command. The Linux head command prints the first lines of one or more files to standard output. By default, it shows the first 10 lines.
Show only the bottom three fruits from the file.
To show only the bottom three fruits we will use the tail command. Tail is a command which prints the last few lines (10 lines by default) of a certain file.
To create another file Colors.txt and view the content.
Add content in Colors.txt (One in each line) - Red, Pink, White, Black, Blue, Orange, Purple, and Grey.
We used touch and vim commands for creating the colors.txt file
Add content in Colors.txt (One in each line) - Red, Pink, White, Black, Blue, Orange, Purple, and Grey.
To find the difference between the fruits.txt and Colors.txt files.
diffCommand to find the difference between the content of two files.
Thank you for reading this blog. I hope you learned something new today! If you found this blog helpful, please like, share, and follow me for more blog posts like this in the future.
— Happy Learning !!!
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