1.\" $OpenBSD: setreuid.2,v 1.7 2008/08/04 07:08:23 jmc Exp $ 2.\" 3.\" Copyright (c) 1980, 1991, 1993, 1994 4.\" The Regents of the University of California. All rights reserved. 5.\" 6.\" Redistribution and use in source and binary forms, with or without 7.\" modification, are permitted provided that the following conditions 8.\" are met: 9.\" 1. Redistributions of source code must retain the above copyright 10.\" notice, this list of conditions and the following disclaimer. 11.\" 2. Redistributions in binary form must reproduce the above copyright 12.\" notice, this list of conditions and the following disclaimer in the 13.\" documentation and/or other materials provided with the distribution. 14.\" 3. Neither the name of the University nor the names of its contributors 15.\" may be used to endorse or promote products derived from this software 16.\" without specific prior written permission. 17.\" 18.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 19.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 20.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 21.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 22.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 23.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 24.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 25.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 26.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 27.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 28.\" SUCH DAMAGE. 29.\" 30.\" @(#)setreuid.2 8.2 (Berkeley) 4/16/94 31.\" 32.Dd $Mdocdate: August 4 2008 $ 33.Dt SETREUID 2 34.Os 35.Sh NAME 36.Nm setreuid 37.Nd set real and effective user IDs 38.Sh SYNOPSIS 39.Fd #include <unistd.h> 40.Ft int 41.Fn setreuid "uid_t ruid" "uid_t euid" 42.Sh DESCRIPTION 43The real and effective user IDs of the 44current process are set according to the arguments. 45The saved user ID will be set to the new value of the real 46user ID if a real user ID is specified and either 47the new real user ID value is different from the current value 48or the effective user ID is changed to a value other than the 49current saved user ID. 50.Pp 51Unprivileged users may change either user ID to the current value 52of the real, effective, or saved user ID. 53Only the superuser may make other changes. 54.Pp 55Supplying a value of -1 for either the real or effective 56user ID forces the system to substitute the current 57ID in place of the -1 parameter. 58.Pp 59The 60.Fn setreuid 61function was intended to allow swapping the real and 62effective user IDs in set-user-ID programs to temporarily relinquish 63the set-user-ID value. 64This purpose is now better served by the use of the 65.Xr seteuid 2 66function. 67.Pp 68When setting the real and effective user IDs to the same value, the 69.Xr setuid 2 70function is preferred. 71.Sh RETURN VALUES 72Upon successful completion, a value of 0 is returned. 73Otherwise, a value of -1 is returned and 74.Va errno 75is set to indicate the error. 76.Sh ERRORS 77.Bl -tag -width Er 78.It Bq Er EPERM 79The current process is not the superuser and a change 80other than changing the effective user ID to the real user ID 81was specified. 82.El 83.Sh SEE ALSO 84.Xr getuid 2 , 85.Xr seteuid 2 , 86.Xr setregid 2 , 87.Xr setresuid 2 , 88.Xr setuid 2 89.Sh STANDARDS 90The 91.Fn setreuid 92function conforms to the 93.St -p1003.1-2001 94and 95.St -xpg4.3 . 96specifications. 97.Pp 98Note, however, that prior to 99.St -p1003.1-2001 , 100the 101.Fn setreuid 102function was not a part of the 103.St -p1003.1 104specification. 105As a result, it may not be implemented on all systems. 106.Sh HISTORY 107The 108.Fn setreuid 109function call appeared in 110.Bx 4.2 . 111A semantically different version appeared in 112.Bx 4.4 . 113The current version, with the original semantics restored, appeared in 114.Ox 3.3 . 115.Sh CAVEATS 116The 117.Fn setreuid 118function predates 119.Tn POSIX 120saved user IDs. 121This implementation changes the saved user ID to the new value of 122the real user ID only if the real user ID is specified and either 123changed 124or the effective user ID is changed to a value other than the current 125saved user ID. 126Other implementations may behave differently. 127