getuid - Man Page

get a real 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>

uid_t getuid(void);


The getuid() function shall return the real user ID of the calling process. The getuid() function shall not modify errno.

Return Value

The getuid() function shall always be successful and no return value is reserved to indicate the error.


No errors are defined.

The following sections are informative.


Setting the Effective User ID to the Real User ID

The following example sets the effective user ID of the calling process to the real user ID.

#include <unistd.h>

Application Usage



In a conforming environment, getuid() will always succeed. It is possible for implementations to provide an extension where a process in a non-conforming environment will not be associated with a user or group ID. It is recommended that such implementations return (uid_t)-1 and set errno to indicate such an environment; doing so does not violate this standard, since such an environment is already an extension.

Future Directions


See Also

getegid(), geteuid(), getgid(), setegid(), seteuid(), 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), getlogin(3p), getpwuid(3p), id(1p), setegid(3p), seteuid(3p), setgid(3p), setregid(3p), setreuid(3p), setuid(3p), unistd.h(0p).

2017 IEEE/The Open Group POSIX Programmer's Manual