The
setuid() function sets the real and effective user IDs and the saved set-user-ID of the current process to the specified value. The
setuid() 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
setgid() function sets the real and effective group IDs and the saved set-group-ID of the current process to the specified value. The
setgid() 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. Supplementary group IDs remain unchanged.
The
seteuid() function (
setegid()) 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
intro(2) and
execve(2)); 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-group-ID.