ultrix man page for geteuid

getuid(2)							System Calls Manual							 getuid(2)

Name
       getuid, geteuid - get user identity

Syntax
       #include <sys/types.h>
       #include <unistd.h>

       uid = getuid()
       uid_t uid;

       euid = geteuid()
       uid_t euid;

Description
       The system call returns the real user ID of the current process, 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 to determine the real-user-id of the process which invoked them.

Environment
   System Five
       Differs from the System V definition in that the return values are of type int, instead of unsigned short.

   POSIX
       When your program is compiled in POSIX mode, the and functions return a value of type uid_t.  The and functions	return	a  value  of  type
       gid_t.

See Also
       getgid(2), setreuid(2)

																	 getuid(2)