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       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

       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

       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

       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

   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),


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