from small one page howto to huge articles all in one place
 

search text in:





Poll
Which kernel version do you use?





poll results

Last additions:
using iotop to find disk usage hogs

using iotop to find disk usage hogs

words:

887

views:

185934

userrating:

average rating: 1.7 (102 votes) (1=very good 6=terrible)


May 25th. 2007:
Words

486

Views

250337

why adblockers are bad


Workaround and fixes for the current Core Dump Handling vulnerability affected kernels

Workaround and fixes for the current Core Dump Handling vulnerability affected kernels

words:

161

views:

137481

userrating:

average rating: 1.4 (42 votes) (1=very good 6=terrible)


April, 26th. 2006:

Druckversion
You are here: manpages





SETUID

Section: Linux Programmer's Manual (2)
Updated: 2017-09-15
Index Return to Main Contents
 

NAME

setuid - set user identity  

SYNOPSIS

#include <sys/types.h>
#include <unistd.h>

int setuid(uid_t uid);  

DESCRIPTION

setuid() sets the effective user ID of the calling process. If the calling process is privileged (more precisely: if the process has the CAP_SETUID capability in its user namespace), the real UID and saved set-user-ID are also set.

Under Linux, setuid() is implemented like the POSIX version with the _POSIX_SAVED_IDS feature. This allows a set-user-ID (other than root) program to drop all of its user privileges, do some un-privileged work, and then reengage the original effective user ID in a secure manner.

If the user is root or the program is set-user-ID-root, special care must be taken. The setuid() function checks the effective user ID of the caller and if it is the superuser, all process-related user ID's are set to uid. After this has occurred, it is impossible for the program to regain root privileges.

Thus, a set-user-ID-root program wishing to temporarily drop root privileges, assume the identity of an unprivileged user, and then regain root privileges afterward cannot use setuid(). You can accomplish this with seteuid(2).  

RETURN VALUE

On success, zero is returned. On error, -1 is returned, and errno is set appropriately.

Note: there are cases where setuid() can fail even when the caller is UID 0; it is a grave security error to omit checking for a failure return from setuid().  

ERRORS

EAGAIN
The call would change the caller's real UID (i.e., uid does not match the caller's real UID), but there was a temporary failure allocating the necessary kernel data structures.
EAGAIN
uid does not match the real user ID of the caller and this call would bring the number of processes belonging to the real user ID uid over the caller's RLIMIT_NPROC resource limit. Since Linux 3.1, this error case no longer occurs (but robust applications should check for this error); see the description of EAGAIN in execve(2).
EINVAL
The user ID specified in uid is not valid in this user namespace.
EPERM
The user is not privileged (Linux: does not have the CAP_SETUID capability) and uid does not match the real UID or saved set-user-ID of the calling process.
 

CONFORMING TO

POSIX.1-2001, POSIX.1-2008, SVr4. Not quite compatible with the 4.4BSD call, which sets all of the real, saved, and effective user IDs.  

NOTES

Linux has the concept of the filesystem user ID, normally equal to the effective user ID. The setuid() call also sets the filesystem user ID of the calling process. See setfsuid(2).

If uid is different from the old effective UID, the process will be forbidden from leaving core dumps.

The original Linux setuid() system call supported only 16-bit user IDs. Subsequently, Linux 2.4 added setuid32() supporting 32-bit IDs. The glibc setuid() wrapper function transparently deals with the variation across kernel versions.  

C library/kernel differences

At the kernel level, user IDs and group IDs are a per-thread attribute. However, POSIX requires that all threads in a process share the same credentials. The NPTL threading implementation handles the POSIX requirements by providing wrapper functions for the various system calls that change process UIDs and GIDs. These wrapper functions (including the one for setuid()) employ a signal-based technique to ensure that when one thread changes credentials, all of the other threads in the process also change their credentials. For details, see nptl(7).  

SEE ALSO

getuid(2), seteuid(2), setfsuid(2), setreuid(2), capabilities(7), credentials(7), user_namespaces(7)  

COLOPHON

This page is part of release 4.13 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at https://www.kernel.org/doc/man-pages/.


 

Index

NAME
SYNOPSIS
DESCRIPTION
RETURN VALUE
ERRORS
CONFORMING TO
NOTES
C library/kernel differences
SEE ALSO
COLOPHON





Support us on Content Nation
rdf newsfeed | rss newsfeed | Atom newsfeed
- Powered by LeopardCMS - Running on Gentoo -
Copyright 2004-2020 Sascha Nitsch Unternehmensberatung GmbH
Valid XHTML1.1 : Valid CSS : buttonmaker
- Level Triple-A Conformance to Web Content Accessibility Guidelines 1.0 -
- Copyright and legal notices -
Time to create this page: 16.7 ms