NAME

       seteuid, setegid - set effective user or group ID

SYNOPSIS

       #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 <= 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 to indicate the
       error.

       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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