bsd man page for getuid

GETUID(2)							System Calls Manual							 GETUID(2)

NAME
       getuid, geteuid - get user identity

SYNOPSIS
       #include <sys/types.h>

       uid = getuid()
       uid_t uid;

       euid = geteuid()
       uid_t euid;

DESCRIPTION
       Getuid returns the real user ID of the current process, geteuid the effective user ID.

       The  real  user ID identifies the person who is logged in.  The effective user ID gives the process additional permissions during execution
       of "set-user-ID" mode processes, which use getuid to determine the real-user-id of the process that invoked them.

SEE ALSO
       getgid(2), setreuid(2)

4th Berkeley Distribution					  January 7, 1986							 GETUID(2)