As you might have noticed in the part about octal notation, we always start the notation with a zero (0775, 0640, and so on). Why do we include the zero if we do not use it? That position is reserved for special file permissions: SUID, SGID, and the sticky bit. They have a similar octal notation (where SUID is 4, SGID is 2, and the sticky bit is 1) and are used in the following manner:
|
Files |
Directories |
|
|
SUID |
Files are executed with the permissions of the owner, regardless of which user executes it. |
Does nothing. |
|
SGID |
Files are executed with the permissions of the group, regardless of which user executes it. |
Files that are created in this directory get the same group as the directory. |
|
Sticky bit |
Does nothing. |
User can only delete their own files within this directory. See the /tmp/ directory for its most famous use. |