All About Linux Permission with special permissions includes SUDI, SGID, and Sticky Bit. Chmod WhoWhatWhich file | Directory Who – Represents identities: u, g, o, a (User, Group, Other, All) What – Represents Actions: +, -, = (Add, Remove, Set Exact) Which – Represents Access Levels: r, w, x (Read, Write, Execute) chmod ug+rw file.txt Special permissions make up a fourth access level in addition to user, group, and other. Special permissions allow for additional privileges over the standard permission sets (as the name suggests). There is a special permission option for each access level discussed previously. Commonly noted as SUID, the special permission for the user access level has a single function: A file with SUID always executes as the user who owns the file, regardless of the user passing the command. If the file owner doesn't have execute permissions, then use an uppercase S here. Commonly noted as SGID, this special permission has a couple of functions: If set on a file, it allows the file to be executed as the group that owns the file (similar to SUID) If set on a directory, any files created in the directory will have their group ownership set to that of the directory owner The last special permission has been dubbed the "sticky bit." This permission does not affect individual files. However, at the directory level, it restricts file deletion. Only the owner (and root) of a file can remove the file within that directory.

2. - File
d Directory
l Link
Owner Group User/Others
r File
w Directory
x Link

4. 7 rwx 111
6 rw- 110
5 r-x 101
4 r-- 100
3 -wx 011
2 -w- 010
1 --x 001
0 --- 000
Symbolic Numeric Permission
--- 0 None
--x 1 Execute
-w- 2 Write
-wx 3 Write + Execute
r-- 4 Read
r-x 5 Read + Execute
rw- 6 Read + Write
rwx 7 Read + Write + Execute