OpenDarwin 7.2.1 - man page for issetugid (opendarwin section 2)

ISSETUGID(2)			     BSD System Calls Manual			     ISSETUGID(2)

NAME
     issetugid -- is current executable running setuid or setgid

SYNOPSIS
     #include <unistd.h>

     int
     issetugid(void);

DESCRIPTION
     The issetugid() function returns 1 if the process was made setuid or setgid as the result of
     the last execve() system call.  Otherwise it returns 0.

     This system call exists so that library routines (inside libc, libtermlib, or other
     libraries) can gaurantee safe behavior when used inside setuid or setgid programs.  Some
     library routines may not be passed sufficient information to know if the current program was
     started setuid or setgid because higher level calling code may have made changes to the uid
     or the euid.  In particular, it is wise to use this call to determine if a pathname returned
     from a getenv() call may safely be used to open() the specified file.

     issetugid() is unaffected by calls to setuid(), fork(), and other such calls.  It is only
     controlled by execve().

ERRORS
     The issetugid() function is always successful, and no return value is reserved to indicate
     an error.

SEE ALSO
     execve(2), setuid(2), seteuid(2,) setgid(2), setegid(2)

HISTORY
     A lstat() function call appeared in OpenBSD 2.0

OpenBSD 2.0				 August, 25 1996			      OpenBSD 2.0