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():
           _POSIX_C_SOURCE >= 200112L
               || /* Glibc versions <= 2.19: */ _BSD_SOURCE

DESCRIPTION

       seteuid()  sets  the  effective  user ID of the calling process.  Unprivileged 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  In  the  case  of  seteuid():  the calling process is not privileged (does not have the CAP_SETUID
              capability in its user namespace) and euid does not  match  the  current  real  user  ID,  current
              effective user ID, or current saved set-user-ID.

              In  the  case  of  setegid():  the calling process is not privileged (does not have the CAP_SETGID
              capability in its user namespace) and egid does not match  the  current  real  group  ID,  current
              effective group ID, or current saved set-group-ID.

CONFORMING TO

       POSIX.1-2001, POSIX.1-2008, 4.3BSD.

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  setresgid(-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 differences
       On  Linux,  seteuid()  and  setegid()  are  implemented  as  library  functions  that call, respectively,
       setreuid(2) and setregid(2).

SEE ALSO

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

COLOPHON

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Linux                                              2017-09-15                                         SETEUID(2)