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The
function sets the real and effective user IDs and the saved set-user-ID
of the current process to the specified value. The function is permitted
if the specified ID is equal to the real user ID of the process, or if
the effective user ID is that of the super user. The function sets the
real and effective group IDs and the saved set-group-ID of the current process
to the specified value. The function is permitted if the specified ID is
equal to the real group ID of the process, or if the effective user ID
is that of the super user. The function sets the effective user ID (group
ID) of the current process. The effective user ID may be set to the value
of the real user ID or the saved set-user-ID (see and in this way, the
effective user ID of a set-user-ID executable may be toggled by switching
to the real user ID, then re-enabled by reverting to the set-user-ID value.
Similarly, the effective group ID may be set to the value of the real group
ID or the saved set-user-ID.
Upon success, these functions return
0; otherwise -1 is returned. If the user is not the super user, or the uid
specified is not the real, effective ID, or saved ID, these functions return
-1.
The and functions are compliant with the specification
with not defined. The and functions are extensions based on the concept
of and have been proposed for a future revision of the standard.
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