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


       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

       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.


       EPERM  The  calling  process  is  not  privileged  (Linux:  does  not  have the CAP_SETUID
              capability in the case of seteuid(), or the CAP_SETGID capability in  the  case  of
              setegid())  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).


       4.3BSD, POSIX.1-2001.


       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 libc4, libc5 and 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 (dependeing  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


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


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