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Linux 2.6 - man page for seteuid (linux section 2)

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SETEUID(2)			    Linux Programmer's Manual			       SETEUID(2)

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

DESCRIPTION
       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
       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.

ERRORS
       EPERM  The calling process is not privileged (Linux: does not have the CAP_SETUID capabil-
	      ity in the case of seteuid(), or the CAP_SETGID capability in  the  case	of  sete-
	      gid()) 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).

CONFORMING TO
       4.3BSD, POSIX.1-2001.

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 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
       this.

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

COLOPHON
       This  page  is  part of release 3.55 of the Linux man-pages project.  A description of the
       project,    and	  information	 about	  reporting    bugs,	can    be    found     at
       http://www.kernel.org/doc/man-pages/.

Linux					    2012-07-02				       SETEUID(2)
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