setreuid(3p) — Linux manual page


SETREUID(3P)            POSIX Programmer's Manual           SETREUID(3P)

PROLOG         top

       This manual page is part of the POSIX Programmer's Manual.  The
       Linux implementation of this interface may differ (consult the
       corresponding Linux manual page for details of Linux behavior),
       or the interface may not be implemented on Linux.

NAME         top

       setreuid — set real and effective user IDs

SYNOPSIS         top

       #include <unistd.h>

       int setreuid(uid_t ruid, uid_t euid);

DESCRIPTION         top

       The setreuid() function shall set the real and effective user IDs
       of the current process to the values specified by the ruid and
       euid arguments. If ruid or euid is -1, the corresponding
       effective or real user ID of the current process shall be left

       A process with appropriate privileges can set either ID to any
       value.  An unprivileged process can only set the effective user
       ID if the euid argument is equal to either the real, effective,
       or saved user ID of the process.

       If the real user ID is being set (ruid is not -1), or the
       effective user ID is being set to a value not equal to the real
       user ID, then the saved set-user-ID of the current process shall
       be set equal to the new effective user ID.

       It is unspecified whether a process without appropriate
       privileges is permitted to change the real user ID to match the
       current effective user ID or saved set-user-ID of the process.

RETURN VALUE         top

       Upon successful completion, 0 shall be returned. Otherwise, -1
       shall be returned and errno set to indicate the error.

ERRORS         top

       The setreuid() function shall fail if:

       EINVAL The value of the ruid or euid argument is invalid or out-

       EPERM  The current process does not have appropriate privileges,
              and either an attempt was made to change the effective
              user ID to a value other than the real user ID or the
              saved set-user-ID or an attempt was made to change the
              real user ID to a value not permitted by the

       The following sections are informative.

EXAMPLES         top

   Setting the Effective User ID to the Real User ID
       The following example sets the effective user ID of the calling
       process to the real user ID, so that files created later will be
       owned by the current user. It also sets the saved set-user-ID to
       the real user ID, so any future attempt to set the effective user
       ID back to its previous value will fail.

           #include <unistd.h>
           #include <sys/types.h>
           setreuid(getuid(), getuid());



RATIONALE         top

       Earlier versions of this standard did not specify whether the
       saved set-user-ID was affected by setreuid() calls. This version
       specifies common existing practice that constitutes an important
       security feature. The ability to set both the effective user ID
       and saved set-user-ID to be the same as the real user ID means
       that any security weakness in code that is executed after that
       point cannot result in malicious code being executed with the
       previous effective user ID. Privileged applications could already
       do this using just setuid(), but for non-privileged applications
       the only standard method available is to use this feature of



SEE ALSO         top

       getegid(3p), geteuid(3p), getgid(3p), getuid(3p), setegid(3p),
       seteuid(3p), setgid(3p), setregid(3p), setuid(3p)

       The Base Definitions volume of POSIX.1‐2017, unistd.h(0p)

COPYRIGHT         top

       Portions of this text are reprinted and reproduced in electronic
       form from IEEE Std 1003.1-2017, Standard for Information
       Technology -- Portable Operating System Interface (POSIX), The
       Open Group Base Specifications Issue 7, 2018 Edition, Copyright
       (C) 2018 by the Institute of Electrical and Electronics
       Engineers, Inc and The Open Group.  In the event of any
       discrepancy between this version and the original IEEE and The
       Open Group Standard, the original IEEE and The Open Group
       Standard is the referee document. The original Standard can be
       obtained online at .

       Any typographical or formatting errors that appear in this page
       are most likely to have been introduced during the conversion of
       the source files to man page format. To report such errors, see .

IEEE/The Open Group               2017                      SETREUID(3P)

Pages that refer to this page: unistd.h(0p)getegid(3p)geteuid(3p)getgid(3p)getuid(3p)setegid(3p)seteuid(3p)setgid(3p)setregid(3p)setuid(3p)