.\" Copyright (C), 1994, Graeme W. Wilford. (Wilf.) .\" .\" Permission is granted to make and distribute verbatim copies of this .\" manual provided the copyright notice and this permission notice are .\" preserved on all copies. .\" .\" Permission is granted to copy and distribute modified versions of this .\" manual under the conditions for verbatim copying, provided that the .\" entire resulting derived work is distributed under the terms of a .\" permission notice identical to this one .\" .\" Since the Linux kernel and libraries are constantly changing, this .\" manual page may be incorrect or out-of-date. The author(s) assume no .\" responsibility for errors or omissions, or for damages resulting from .\" the use of the information contained herein. The author(s) may not .\" have taken the same level of care in the production of this manual, .\" which is licensed free of charge, as they might when working .\" professionally. .\" .\" Formatted or processed versions of this manual, if unaccompanied by .\" the source, must acknowledge the copyright and authors of this work. .\" .\" Fri Jul 29th 12:56:44 BST 1994 Wilf. (G.Wilford@ee.surrey.ac.uk) .\" .TH SETUID 2 "29 July 1994" "Linux 1.1.36" "Linux Programmer's Manual" .SH NAME setuid \- set user identity .SH SYNOPSIS .B #include .sp .BI "int setuid(uid_t " uid ) .SH DESCRIPTION .B setuid sets the effective user ID of the current process. If the caller is the superuser, the real and saved user ID's are also set. Under Linux, .B setuid is implemented like SYSV with SAVED_IDS. This allows a setuid (other than root) program to drop all of it's user privileges, do some un-privileged work, and then re-engage the original effective user ID in a secure manner. If the user is root or the program is setuid root, special care must be taken. The .B setuid function checks the effective uid of the caller and if it is the superuser, all process related user ID's are set to .IR uid . After this has occurred, it is impossible for the program to regain root privileges. .SH "RETURN VALUE" On success, zero is returned. On error, \-1 is returned, and .I errno is set appropriately. .SH ERRORS .TP 0.8i .B EPERM The user is not the super-user, and .I uid does not match the effective or saved user ID of the calling process. .SH "CONFORMING TO" System V .SH "SEE ALSO" .BR getuid "(2), " setreuid "(2), " seteuid (2)