| GETUID(2) | System Calls Manual | GETUID(2) | 
getuid, geteuid —
#include <unistd.h>
uid_t
  
  getuid(void);
uid_t
  
  geteuid(void);
getuid() function returns the real user ID of the
  calling process. The geteuid() function returns the
  effective user ID of the calling process.
The real user ID is that of the user who has invoked the program.
    As the effective user ID gives the process additional permissions during
    execution of “set-user-ID” mode processes,
    getuid() is used to determine the real-user-id of
    the calling process.
getuid() and geteuid()
  functions are always successful, and no return value is reserved to indicate
  an error.
geteuid() and getuid()
  functions conform to IEEE Std 1003.1-1990
  (“POSIX.1”).
getuid() function appeared in
  Version 1 AT&T UNIX.
| September 1, 2019 | NetBSD 9.3 |