CheatSheet
- 3 positions in the permission string:
- 1st position: Owner
- 2nd position: Group
- 3rd position: Others
- All useful combinations of permissions:
| Permission | Number | Symbol |
|---|---|---|
| No access | 0 | - |
| Read | 4 | r |
| Write | 2 | w |
| Execute | 1 | x |
| Read + Write | 6 | rw |
| Read + Exec | 5 | rx |
| Read + Write + Exec | 7 | rwx |
Permissions such as “Write + Execute” are not useful because if we don’t want a user to read a file, we should not allow them to write to it either.
Meaning of
umask xxxxSome useful commands:
| To Do | How To Do |
|---|---|
| Prevent everyone else from reading a file | chmod 600 filename |
| Prevent everyone else from entering a dir | chmod 600 dirname |
| Prevent everyone else from reading dir content | chmod 700 dirname |
| Prevent everyone else from reading every new file and dir | umask 0077 |