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Linux Permission Bits

Linux uses a permissions model to control access to files and directories. Permission bits are used to represent the permissions associated with a file or directory. This tutorial will introduce you to Linux permission bits, the concept of file ownership, and the basic commands for managing permissions.

Understanding Permission Bits

Each file and directory in a Linux system has three types of permissions:

Read (r): The ability to view the contents of a file or list the contents of a directory.
Write (w): The ability to modify a file or add/remove files in a directory.
Execute (x): The ability to run a file as a program or enter a directory.

These permissions are represented by permission bits, with each bit representing one of the permissions (read, write, and execute).

Permission Categories

There are three categories of users who can have permissions for a file or directory:

Owner (u): The user who created the file or directory.
Group (g): A set of users who share the same permissions for the file or directory.
Others (o): All other users who are not the owner or part of the group.

Numeric Representation

Each permission can be represented by a number:

Read (r): 4
Write (w): 2
Execute (x): 1

To calculate the numeric value of a permission set, simply add the numbers of the granted permissions. For example, a permission set of read and write (rw-) would have a numeric value of 6 (4 + 2).

Viewing Permissions

To view the permissions of a file or directory, use the ls command with the -l option:

ls -l

The output will show the permissions in the following format:

-rw-r--r-- 1 user group 1024 May 10 12:34 example.txt

The first column represents the permission bits. The characters indicate the permission type (r, w, x, or -). The permission bits are grouped in sets of three, representing owner, group, and others permissions respectively.

Changing Permissions

To change the permissions of a file or directory, use the chmod command. You can specify the permissions using numeric values or using symbolic notation.

Numeric notation:

chmod 640 example.txt

This sets the permissions for the owner to read and write (6), the group to read (4), and others to have no access (0).

Symbolic notation:

chmod u=rw,g=r,o= example.txt

This has the same effect as the previous command, using letters to represent the permissions.

Changing Ownership

To change the owner and group of a file or directory, use the chown command:

chown user:group example.txt

This will change the owner to 'user' and the group to 'group'.

In conclusion, Linux permission bits allow you to control access to files and directories. By understanding and managing these permissions, you can ensure the appropriate level of security for your files and directories.

How to set file permissions in Linux: File permissions in Linux are set using the chmod command. For example:
```
chmod permissions file_name
```
chmod command in Linux for changing permission bits: Use chmod to change file permissions. For example, to give read and write permissions to the owner:
```
chmod u+rw file_name
```
Advanced file permission settings in Linux: Advanced settings include setting the setuid (suid), setgid (sgid), and sticky bit. For example, to set the suid bit:
```
chmod u+s file_name
```