seteuid, setegid - set effective user or group ID


   #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


   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".


   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().


   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.


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


   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).


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


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   description  of  the project, information about reporting bugs, and the
   latest    version    of    this    page,    can     be     found     at


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