setuid(2) setuid(2)
NAME
setuid, setgid - set user and group IDs
SYNOPSIS
#include <sys/types.h>
#include <unistd.h>
int setuid(uid_t uid);
int setgid(gid_t gid);
DESCRIPTION
The setuid system call sets the real user ID, effective user
ID, and saved user ID of the calling process. The setgid
system call sets the real group ID, effective group ID, and
saved group ID of the calling process.
At login time, the real user ID, effective user ID, and saved
user ID of the login process are set to the login ID of the
user responsible for the creation of the process. The same is
true for the real, effective, and saved group IDs; they are
set to the group ID of the user responsible for the creation
of the process.
When a process calls exec(2) to execute a file (program), the
user and/or group identifiers associated with the process can
change:
The real user and group IDs are always set to the real
user and group IDs of the process calling exec.
The saved user and group IDs of the new process are
always set to the effective user and group IDs of the
process calling exec.
If the file executed is not a set-user-ID or set-group-
ID file, the effective user and group IDs of the new
process are set to the effective user and group IDs of
the process calling exec.
If the file executed is a set-user-ID file, the
effective user ID of the new process is set to the owner
ID of the executed file.
If the file executed is a set-group-ID file, the
effective group ID of the new process is set to the
group ID of the executed file.
Copyright 1994 Novell, Inc. Page 1
setuid(2) setuid(2)
The following subsections describe the behavior of setuid and
setgid with respect to the three types of user and group IDs.
setuid
If the calling process has the P_SETUID privilege, the real,
effective, and saved user IDs are set to the uid parameter.
If the calling process does not have the P_SETUID privilege,
but uid is either the real user ID or the saved user ID of the
calling process, the effective user ID is set to uid.
setgid
If the calling process has the P_SETUID privilege, the real,
effective, and saved group IDs are set to the gid parameter.
If the calling process does not have the P_SETUID privilege,
but gid is either the real group ID or the saved group ID of
the calling process, the effective group ID is set to gid.
Return Values
On success, setuid and setgid return 0. On failure, setuid
and setgid return -1 and set errno to identify the error.
Errors
In the following conditions, setuid and setgid fail and set
errno to:
EPERM For setuid, the calling process does not have the
P_SETUID privilege and the uid parameter does not
match either the real or saved user IDs. For
setgid, the calling process does not have the
P_SETUID privilege and the gid parameter does not
match either the real or saved group IDs.
EINVAL The uid or gid is out of range.
REFERENCES
exec(2), getgroups(2), getuid(2), intro(2), stat(5)
NOTICES
Considerations for Threads Programming
This ID number is an attribute of the containing process and
is shared by sibling threads.
Copyright 1994 Novell, Inc. Page 2