• In Linux, permissions are like keys that control access to files and directories. These permissions are assigned to both users and groups, much like keys being distributed to specific individuals and teams within an organization.
• Each user can belong to multiple groups, and being part of a group grants additional access rights, allowing users to perform specific actions on files and directories.
• Every file and directory has an owner (a user) and is associated with a group.

Types of Permission

1. Read: The right/power to read or see contents of file
2. Write: The right/power to edit the file
3. Execute: The right/power to run script file.

ls -l : It is used to see the file and folder permissions.

NOTE: The ls can traverse the directory only if the directory has execute permission.

Understanding output of ls -l

$ ls -l /etc/passwd

- rwx rw- r--   1 root root 1641 May  4 23:42 /etc/passwd
- --- --- ---   |  |    |    |   |__________|
|  |   |   |    |  |    |    |        |_ Date
|  |   |   |    |  |    |    |__________ File Size
|  |   |   |    |  |    |_______________ Group
|  |   |   |    |  |____________________ User
|  |   |   |    |_______________________ Number of hard links
|  |   |   |_ Permission of others (read)
|  |   |_____ Permissions of the group (read, write)
|  |_________ Permissions of the owner (read, write, execute)
|____________ File type (- = File, d = Directory, l = Link, ... )

Changing the permission

To change the permission of a file we need to use the command chmod .

Permission group references (u: Owner, g: Group, o: Others, a: all user) either a [+] or a [-] to add remove the designated permissions

$ ls -l shell

-rwxr-x--x   1 cry0l1t3 htbteam 0 May  4 22:12 shell

$ chmod a+r shell && ls -l shell

-rwxr-xr-x   1 cry0l1t3 htbteam 0 May  4 22:12 shell

In the above command read permission is given to all users.