chmod Command In Linux | How to Change Permission In Linux | Linux Basic Commands | SN Linux
In this video we will learn about chmod Command In Linux | How to Change Permission In Linux | Linux Basic Commands | SN Linux
The chmod command in Unix and Linux systems is used to change the file mode bits of a file or directory, which determines the permissions granted to users. Understanding chmod is crucial for managing file access and security. Here’s a detailed explanation:
File Permissions Overview
Each file and directory has three types of permissions:
Read (r): Permission to read the file or list the directory.
Write (w): Permission to modify the file or add/remove files in the directory.
Execute (x): Permission to execute the file (if it's a program or script) or access the directory.
These permissions are set for three different categories of users:
Owner (u): The user who owns the file.
Group (g): The group that the file belongs to.
Others (o): All other users.
Using chmod
The chmod command can be used in two primary ways: symbolic mode and numeric (octal) mode.
1. Symbolic Mode
In symbolic mode, you specify the category of users and the permissions you want to change using letters.
Syntax:
bash
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chmod [who][operator][permissions] file
who: u (user), g (group), o (others), a (all)
operator: + (add), - (remove), = (set exactly)
permissions: r (read), w (write), x (execute)
Examples:
Add execute permission for the owner:
bash
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chmod u+x filename
Remove write permission for the group:
bash
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chmod g-w filename
Set read permission for others:
bash
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chmod o=r filename
2. Numeric (Octal) Mode
In numeric mode, you use numbers to set permissions. Each permission corresponds to a number:
Read (r) = 4
Write (w) = 2
Execute (x) = 1
You combine these numbers to set the desired permissions. Each category (owner, group, others) gets its own digit.
Syntax:
bash
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chmod [permissions] file
Examples:
Set permissions to read and write for the owner, and read for the group and others:
bash
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chmod 644 filename
Breakdown:
Owner: 6 (4+2 for read and write)
Group: 4 (read)
Others: 4 (read)
Set permissions to read, write, and execute for the owner, and read and execute for group and others:
bash
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chmod 755 filename
Breakdown:
Owner: 7 (4+2+1 for read, write, and execute)
Group: 5 (4+1 for read and execute)
Others: 5 (4+1 for read and execute)
Recursive Changes
You can also change permissions recursively for directories and their contents using the -R option.
Example:
bash
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chmod -R 755 directoryname
This command sets the permissions of the directory and all its files and subdirectories.
Special Permissions
There are additional permissions that can be set:
Setuid (s): When set on an executable file, the process runs with the privileges of the file owner.
bash
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chmod u+s filename
Setgid (s): When set on a directory, files created within inherit the group of the directory.
bash
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chmod g+s directoryname
Sticky Bit (t): When set on a directory, only the owner can delete or rename files within that directory.
bash
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chmod +t directoryname
Viewing Permissions
You can view the current permissions of files and directories using the ls -l command. The output will show a string of characters indicating permissions for each category.
The chmod command is a powerful tool for managing file permissions in Unix/Linux systems. By using symbolic or numeric modes, you can tailor access to files and directories based on user needs, enhancing both functionality and security.
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