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Special Permissions

Special permissions on files and directories: SetUID, SetGID and Sticky bit.
Special Permissions	on a File	on a Directory
SUID or Set User ID	A program is executed with the file owner's permissions (rather than with the permissions of the user who executes it).	Files created in the directory inherit its UID.
SGID or Set Group ID	The effective group of an executing program is the file owner group.	Files created in the directory inherit its GID.
Sticky (bit)	A program sticks in memory after execution.	Any user can create files, but only the owner of a file can delete it.

Permissions as output in columns 2 to 10 of
`ls -l` and their meaning.
Permissions	Meaning
`--S------`	SUID is set, but user (owner) execute is not set.
`--s------`	SUID and user execute are both set.
`-----S---`	SGID is set, but group execute is not set.
`-----s---`	SGID and group execute are both set.
`--------T`	Sticky bit is set, bot other execute is not set.
`--------t`	Sticky bit and other execute are both set.