chmod
The chmod command is short for 'change mode'. It is used to set the read, write and execute permissions of a file for the file owner, those in the file group and everyone else. The file owner and group are set using the chown command.
Numerical
File permissions can be set numerically where numbers between 0 and 7 correspond to the 8 combinations of read (r), write (w) and execute (x).
| Number | Permissions |
|---|---|
| 0 | no permissions (---) |
| 1 | only execute (--x) |
| 2 | only write (-w-) |
| 3 | write and execute (-wx) |
| 4 | read only (r--) |
| 5 | read and execute (r-x) |
| 6 | read and write (rw-) |
| 7 | read, write and execute (rwx) |
Examples
chmod 777 test.txt
This will give read, write and execute permissions to the owner, the group and others.
chmod 664 test.txt
This will give read and write permissions to the owner and group and only read permissions to others.
Symbols
The file permissions can also be set using symbols for read (r), write (w), execute (x), owner (u), group (g), others (o), adding permissions (+), removing permissions (-) and setting permissions (=).
Examples
chmod +x test.sh
This will add execute permissions for everyone for test.sh
chmod ug+x,o=r test.txt
This will add execute permissions for the owner and group and set others' permissions to only read.