|| FreeBSD System Calls Manual
get user identification
Standard C Library (libc, -lc)
#include < unistd.h>
#include < sys/types.h>
() system call returns the real user ID of the calling process. The
() system call 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.
geteuid() system calls are always successful, and no return value is reserved to indicate an error.
getuid() system calls are expected to conform to IEEE Std 1003.1-1990 (“POSIX.1”).
geteuid() functions appeared in Version 7 AT&T UNIX.