SETEUID(2)                          Linux Programmer's Manual                          SETEUID(2)



NAME
       seteuid, setegid - set effective user or group ID

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

       int seteuid(uid_t euid);
       int setegid(gid_t egid);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       seteuid(), setegid():
           _BSD_SOURCE || _POSIX_C_SOURCE >= 200112L || _XOPEN_SOURCE >= 600

DESCRIPTION
       seteuid()  sets the effective user ID of the calling process.  Unprivileged user processes
       may only set the effective user ID to the real user ID, the effective user ID or the saved
       set-user-ID.

       Precisely the same holds for setegid() with "group" instead of "user".

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

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

ERRORS
       EINVAL The target user or group ID is not valid in this user namespace.

       EPERM  The calling process is not privileged (Linux: does not have the CAP_SETUID capabil‐
              ity  in  the  case  of seteuid(), or the CAP_SETGID capability in the case of sete‐
              gid()) and euid (respectively, egid) is not the real user (group) ID, the effective
              user (group) ID, or the saved set-user-ID (saved set-group-ID).

CONFORMING TO
       4.3BSD, POSIX.1-2001.

NOTES
       Setting  the  effective  user  (group) ID to the saved set-user-ID (saved set-group-ID) is
       possible  since  Linux  1.1.37  (1.1.38).   On  an  arbitrary  system  one  should   check
       _POSIX_SAVED_IDS.

       Under glibc 2.0 seteuid(euid) is equivalent to setreuid(-1, euid) and hence may change the
       saved set-user-ID.  Under glibc 2.1 and later it is equivalent to setresuid(-1, euid,  -1)
       and  hence  does  not change the saved set-user-ID.  Analogous remarks hold for setegid(),
       with the difference that the change in implementation from setregid(-1, egid)  to  setres‐
       gid(-1, egid, -1) occurred in glibc 2.2 or 2.3 (depending on the hardware architecture).

       According  to  POSIX.1,  seteuid()  (setegid()) need not permit euid (egid) to be the same
       value as the current effective user (group) ID, and some  implementations  do  not  permit
       this.

   C library/kernel ABI differences
       On  Linux, seteuid() and setegid() are implemented as library functions that call, respec‐
       tively, setreuid(2) and setresgid(2).

SEE ALSO
       geteuid(2),  setresuid(2),  setreuid(2),   setuid(2),   capabilities(7),   credentials(7),
       user_namespaces(7)

COLOPHON
       This  page  is  part of release 3.74 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 http://www.kernel.org/doc/man-pages/.



Linux                                       2014-09-21                                 SETEUID(2)