Changing File Permissions
What do File Permissions Do?
File permissions control the actions that users can perform and which users have access to files and directories
The chmod Command
The chmod command is the command that is actually used to change the permissions of a file or directory
Running the chmod command looks something like this
Changing Permissions Using Numbers
The read, write, and execute permissions are given their own numbers: the execute permission is 1, the write permission is 2, and the read permission and 4.
The sum of these numbers determines the permission combination.
This table contains numbers and their corresponding permissions.
| Number | Command |
|---|---|
| 7 | read, write, execute |
| 6 | read, write |
| 5 | read, execute |
| 4 | read |
| 3 | write, execute |
| 2 | write |
| 1 | execute |
| 0 | no permissions |
The first digit of the chmod command corresponds to the permissions of the owner, the second for the group, and the third is for others.
An example of running the chmod command using digits would look something like this
What this command actually means is described below
- Since the first digit is
7, the owner is given permissions: read, write, and execute. - The second digit being
3means that the group is given the permissions: write, execute. - Finally, the third digit being
5means that others are given permissions: read, execute.
Changing Permissions Using Letters
The read, write, and execute permissions are given the respective letters r, w, and x.
To specify who the permission is being assigned to, a u is used for the owner of the file, g for the group, and o for everyone else, and a for all users.
To assign permissions, a + operator is used. To remove permissions, a - operator is used. To set the permissions, an = operator is used.
To give no permissionms, a --- operator can be attached to whoever the permission is being assigned to.
Using this information, the command previously shown can be rewritten to this command
To give others no permissions, the following command can be ran
To remove the write permission from the group, the following command can be ran
To add the execute permission to others, the following command can be ran