In Linux, file permissions determine who can read, write, or execute a file. Each file and directory in a Linux system has a set of permissions that control access to it.
There are three types of permissions: read, write, and execute. These permissions can be granted or denied to three different groups of users: the owner of the file (user), the group that the file belongs to (group), and all other users (other).
You can view the permissions of a file by using the ls -l command. Here is an example of the output:
-rw-rw-r-- 1 user group 674 Jan 1 12:34 file.txt
The first character (-) indicates the type of file. A - indicates a regular file, d indicates a directory, l indicates a symbolic link, and so on.
The next nine characters (rw-rw-r--) represent the permissions for the file. Each group of three characters represents the permissions for user, group, and other, respectively.
The characters can be either r (read), w (write), x (execute), or - (none). For example, in the above example, the file has read and write permission for the user and group, and read permission for other.
You can use the chmod command to change the permissions of a file. For example, to give read and write permission to the user and group and read permission to other for a file called file.txt, you can use the following command:
chmod 664 file.txt
This is a general overview of how file permissions work in Linux. Consult the documentation and online resources available for more information on the various options and features available for managing file permissions.