There are three categories: User (the file’s owner), Group (the security group you’re in), and Other (for others). Each category allows to establish three permissions: r, w, and x to read, write, and execute a file, respectively. Permissions are denoted by three numbers: 4 for Read, 2 for Write, and 1 for Execute. As a quick reference, here is a table:
| User | Group | Other | |
|---|---|---|---|
| Read = 4 | x | x | x |
| Write = 2 | x | ||
| Execute = 1 | x | x | x |
| Totals | (4+2+1) = 7 | (4 + 1) = 5 | (4 + 1) = 5 |
The single-digit numbers are as follows for all three user categories:
| Octal | String representation | Permissions |
|---|---|---|
| 0 | - - - | no access |
| 1 | - - x | execute |
| 2 | - w - | write |
| 3 | - w x | write and execute |
| 4 | r - - | read |
| 5 | r - x | read and execute |
| 6 | r w - | read and write |
| 7 | r w x | read, write and execute (full access) |
Examples:
- 777 - all can read/write/execute (full access).
- 755 - owner can read/write/execute, group/others can read/execute.
- 644 - owner can read/write, group/others can read only.