seteuid - Man Page

set effective user ID


This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface may differ (consult the corresponding Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.


#include <unistd.h>

int seteuid(uid_t uid);


If uid is equal to the real user ID or the saved set-user-ID, or if the process has appropriate privileges, seteuid() shall set the effective user ID of the calling process to uid; the real user ID and saved set-user-ID shall remain unchanged.

The seteuid() function shall not affect the supplementary group list in any way.

Return Value

Upon successful completion, 0 shall be returned; otherwise, -1 shall be returned and errno set to indicate the error.


The seteuid() function shall fail if:


The value of the uid argument is invalid and is not supported by the implementation.


The process does not have appropriate privileges and uid does not match the real user ID or the saved set-user-ID.

The following sections are informative.



Application Usage



Refer to the RATIONALE section in setuid().

Future Directions


See Also

exec, getegid(), geteuid(), getgid(), getuid(), setegid(), setgid(), setregid(), setreuid(), setuid()

The Base Definitions volume of POSIX.1-2017, <sys_types.h>, <unistd.h>

Referenced By

getegid(3p), geteuid(3p), getgid(3p), getuid(3p), setegid(3p), setgid(3p), setregid(3p), setreuid(3p), setuid(3p), unistd.h(0p).

2017 IEEE/The Open Group POSIX Programmer's Manual