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SETUID(2)                   BSD System Calls Manual                  SETUID(2)

NAME
     setegid, seteuid, setgid, setuid -- set user and group ID

SYNOPSIS
     #include <unistd.h>

     int
     setegid(gid_t egid);

     int
     seteuid(uid_t euid);

     int
     setgid(gid_t gid);

     int
     setuid(uid_t uid);

DESCRIPTION
     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 effective user ID is that of the super user,
     or if the specified user ID is the same as the effective user ID.  If
     not, but the specified user ID is the same as the real user ID, setuid()
     will set the effective user ID to the real user ID.

     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 effective user ID is that of the super user,
     or if the specified group ID is the same as the effective group ID.  If
     not, but the specified group ID is the same as the real group ID,
     setgid() will set the effective group ID to the real group ID.

     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-user-ID.

RETURN VALUES
     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.

ERRORS
     The setegid(), seteuid(), setgid(), and setuid() system calls will fail
     if:

     [EINVAL]           The value of the {group,user} ID argument is invalid
                        and is not supported by the implementation.

     [EPERM]            The process does not have appropriate privileges and
                        the ID argument does not match the real ID or the
                        saved set-{group,user}-ID.

LEGACY SYNOPSIS
     #include <sys/types.h>
     #include <unistd.h>

     The include file <sys/types.h> is necessary for all functions.

SEE ALSO
     getgid(2), getuid(2), compat(5)

STANDARDS
     The setuid() and setgid() functions are compliant with the ISO/IEC
     9945-1:1990 (``POSIX.1'') specification with _POSIX_SAVED_IDS defined,
     with the extensions allowed in section B.4.2.2.  The seteuid() and
     setegid() functions are extensions based on the POSIX concept of
     _POSIX_SAVED_IDS, and have been proposed for a future revision of the
     standard.

4.2 Berkeley Distribution        June 4, 1993        4.2 Berkeley Distribution