Real, effective and saved user id in C program

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LEARN ABOUT FREEBSD

setreuid

SETREUID(2)						      BSD System Calls Manual						       SETREUID(2)

NAME

     setreuid -- set real and effective user ID's

LIBRARY

     Standard C Library (libc, -lc)

SYNOPSIS

     #include <unistd.h>

     int
     setreuid(uid_t ruid, uid_t euid);

DESCRIPTION

     The real and effective user IDs of the current process are set according to the arguments.  If ruid or euid is -1, the current uid is filled
     in by the system.	Unprivileged users may change the real user ID to the effective user ID and vice-versa; only the super-user may make other
     changes.

     If the real user ID is changed (i.e. ruid is not -1) or the effective user ID is changed to something other than the real user ID, then the
     saved user ID will be set to the effective user ID.

     The setreuid() system call has been used to swap the real and effective user IDs in set-user-ID programs to temporarily relinquish the set-
     user-ID value.  This purpose is now better served by the use of the seteuid(2) system call.

     When setting the real and effective user IDs to the same value, the standard setuid() system call is preferred.

RETURN VALUES

     The setreuid() function returns the value 0 if successful; otherwise the value -1 is returned and the global variable errno is set to indi-
     cate the error.

ERRORS

     [EPERM]		The current process is not the super-user and a change other than changing the effective user-id to the real user-id was
			specified.

SEE ALSO

     getuid(2), issetugid(2), seteuid(2), setuid(2)

HISTORY

     The setreuid() system call appeared in 4.2BSD.

BSD
								 February 8, 2001							       BSD

Programming