File Permissions

There are 6 permissions in Linux

These are the standard ones Read write execute

File Type	Owning User	Owning group	Other
d (directory)	rwx	r-x	—

There are 3 special permissions

Permission	effect on directory	effect on file
u+s (suid)	no effect	File executes as the user that owns the file, not as the user that ran the file
g+s (sgid)	Files that are created in the directory have a group owner to match the group owner of the directory	File executes as the group that owns the file.
o+t (sticky)	Users with write access to the directory can remove only files that they own; they cannot remove or force saves to files that other users own	no effect

Sticky bit

This applies only to directories
Only the owning user can delete a file from a directory
Applied with chmod o+t or chmod 1NNN
Identified by a t in permissions for others

Permission will appear as a T if the execute permissions is not set for other. If this permission is set it will appear as lower case

SetGid bit

Set on files and directories
The owning group of a newly created file is derived from the directory that the file is created (for directory)
THe executables run with the permissions of the owning group of the executablers (for files)
To set use chmod g+s /dir or chmod 2NNN /dir or for files chmod g+s /file or chmod 2NNN /file
Identifed by an s in permissions for the owning group

SetUID bit

this is for files only
executables run with permissions of the owning user of the executable
to set use chmod u+s /file or chmod 4NNN /file
identified by an s in the owning user