File permissions in Linux determine who can read, write, or execute a file. Understanding file permissions is fundamental to managing and securing a Linux system. This section will cover how Linux permissions work, how to modify them, and how to interpret the output of the ls -l command.

Understanding Linux File Permissions:

In Linux, every file and directory has three types of permissions:

• Read (r): Allows viewing the contents of the file or listing the contents of a directory.
• Write (w): Allows modifying the contents of the file or adding/removing files from a directory.
• Execute (x): Allows executing the file (if it's a program or script) or entering a directory.

Linux permissions are assigned to three categories of users:

• Owner: The user who owns the file (creator of the file).
• Group: The group that the file belongs to. Each user is a part of a group, and files can be assigned to groups.
• Others: Any other user who is not the owner or a part of the file's group.

Viewing File Permissions:

You can view the permissions of files and directories with the ls -l command: ls -l

$ ls -l file.txt
-rwxr-xr-x 1 user group 1234 Jan 1 12:34 file.txt

Explanation of the output:

• -rwxr-xr-x: This represents the file's permissions.
  • The first character (-) represents the file type: - is a regular file, and d would indicate a directory.
  • The next three characters (rwx) represent the owner's permissions (read, write, execute).
  • The next three characters (r-x) represent the group's permissions (read, execute, but not write).
  • The final three characters (r-x) represent the others' permissions (read, execute, but not write).
• 1: The number of hard links to the file.
• user: The file's owner.
• group: The file's group.
• 1234: The file size in bytes.