osf1 man page for setuid

setuid(2)							System Calls Manual							 setuid(2)

NAME
       setuid - Sets the user ID

SYNOPSIS
       #include <unistd.h>

       int setuid (
	       uid_t user_id );

       Application  developers	may  want  to  specify an #include statement for <sys/types.h> before the one for <unistd.h> if programs are being
       developed for multiple platforms. The additional #include statement is not required on Tru64 UNIX systems or by ISO  or	X/Open	standards,
       but may be required on other vendors' systems that conform to these standards.

STANDARDS
       Interfaces documented on this reference page conform to industry standards as follows:

       setuid(): XSH5.0

       Refer to the standards(5) reference page for more information about industry standards and associated tags.

PARAMETERS
       Specifies the new user ID.

DESCRIPTION
       The setuid() function sets the real user ID, effective user ID, and the saved set user ID to the user_id parameter.

       To  change  the	real user ID, the effective user ID, and the saved set user ID, the calling process must have superuser privilege.  If the
       process does not have appropriate privilege, but the user_id parameter is equal to the real user ID or the saved set user ID, the  setuid()
       function sets the effective user ID to the user_id parameter.  The real user ID and saved set user ID remain unchanged.

RETURN VALUES
       Upon  successful  completion,  the  setuid()  function returns a value of 0 (zero).  Otherwise, the function returns a value of -1 and sets
       errno to indicate the error.

ERRORS
       The setuid() function sets errno to the specified values for the following conditions: [Tru64 UNIX]  The process is attempting an operation
       that  would  exceeds  a	system limit, such as the number of tasks or threads allowed for a user ID.  The value of the user_id parameter is
       invalid.  The process does not have superuser privileges, and the user_id parameter does not match the real user ID or the saved  set  user
       ID.

RELATED INFORMATION
       Functions: exec(2), getuid(2), setgid(2), setreuid(2)

       Standards: standards(5) delim off

																	 setuid(2)