PROLOG | NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | EXAMPLES | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT

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 unchanged.

       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-of-
              range.

       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 implementation.

       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());
           ...

APPLICATION USAGE         top

       None.

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 setreuid().

FUTURE DIRECTIONS         top

       None.

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.1‐2008, unistd.h(0p)

COPYRIGHT         top

       Portions of this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1, 2013 Edition, Standard for Information
       Technology -- Portable Operating System Interface (POSIX), The Open
       Group Base Specifications Issue 7, Copyright (C) 2013 by the
       Institute of Electrical and Electronics Engineers, Inc and The Open
       Group.  (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1
       applied.) 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 http://www.unix.org/online.html .

       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
       https://www.kernel.org/doc/man-pages/reporting_bugs.html .

IEEE/The Open Group                 2013                        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)