1SETREGID(3P)               POSIX Programmer's Manual              SETREGID(3P)
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PROLOG

6       This  manual  page is part of the POSIX Programmer's Manual.  The Linux
7       implementation of this interface may differ (consult the  corresponding
8       Linux  manual page for details of Linux behavior), or the interface may
9       not be implemented on Linux.
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NAME

12       setregid — set real and effective group IDs
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SYNOPSIS

15       #include <unistd.h>
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17       int setregid(gid_t rgid, gid_t egid);
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DESCRIPTION

20       The setregid() function shall set the real and effective group  IDs  of
21       the calling process.
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23       If  rgid  is -1, the real group ID shall not be changed; if egid is -1,
24       the effective group ID shall not be changed.
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26       The real and effective group IDs may be set to different values in  the
27       same call.
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29       Only  a  process  with appropriate privileges can set the real group ID
30       and the effective group ID to any valid value.
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32       A non-privileged process can set either the real group ID to the  saved
33       set-group-ID from one of the exec family of functions, or the effective
34       group ID to the saved set-group-ID or the real group ID.
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36       If the real group ID is being set (rgid is not -1),  or  the  effective
37       group  ID  is being set to a value not equal to the real group ID, then
38       the saved set-group-ID of the current process shall be set equal to the
39       new effective group ID.
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41       Any supplementary group IDs of the calling process remain unchanged.
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RETURN VALUE

44       Upon successful completion, 0 shall be returned. Otherwise, -1 shall be
45       returned and errno set to indicate the error, and neither of the  group
46       IDs are changed.
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ERRORS

49       The setregid() function shall fail if:
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51       EINVAL The  value  of  the  rgid or egid argument is invalid or out-of-
52              range.
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54       EPERM  The process does not have appropriate privileges  and  a  change
55              other than changing the real group ID to the saved set-group-ID,
56              or changing the effective group ID to the real group ID  or  the
57              saved set-group-ID, was requested.
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59       The following sections are informative.
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EXAMPLES

62       None.
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APPLICATION USAGE

65       If a non-privileged set-group-ID process sets its effective group ID to
66       its real group ID, it can only set its effective group ID back  to  the
67       previous  value if rgid was -1 in the setregid() call, since the saved-
68       group-ID is not changed in that case. If rgid was  equal  to  the  real
69       group  ID in the setregid() call, then the saved set-group-ID will also
70       have been changed to the real user ID.
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RATIONALE

73       Earlier versions of this standard did not  specify  whether  the  saved
74       set-group-ID  was  affected by setregid() calls. This version specifies
75       common existing practice that constitutes an  important  security  fea‐
76       ture.  The  ability  to  set both the effective group ID and saved set-
77       group-ID to be the same as the real group ID means  that  any  security
78       weakness  in  code  that  is executed after that point cannot result in
79       malicious code being executed with the  previous  effective  group  ID.
80       Privileged  applications could already do this using just setgid(), but
81       for non-privileged applications the only standard method  available  is
82       to use this feature of setregid().
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FUTURE DIRECTIONS

85       None.
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SEE ALSO

88       exec,  getegid(),  geteuid(), getgid(), getuid(), setegid(), seteuid(),
89       setgid(), setreuid(), setuid()
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91       The Base Definitions volume of POSIX.1‐2017, <unistd.h>
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94       Portions of this text are reprinted and reproduced in  electronic  form
95       from  IEEE Std 1003.1-2017, Standard for Information Technology -- Por‐
96       table Operating System Interface (POSIX), The Open Group Base  Specifi‐
97       cations  Issue  7, 2018 Edition, Copyright (C) 2018 by the Institute of
98       Electrical and Electronics Engineers, Inc and The Open Group.   In  the
99       event of any discrepancy between this version and the original IEEE and
100       The Open Group Standard, the original IEEE and The Open Group  Standard
101       is  the  referee document. The original Standard can be obtained online
102       at http://www.opengroup.org/unix/online.html .
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104       Any typographical or formatting errors that appear  in  this  page  are
105       most likely to have been introduced during the conversion of the source
106       files to man page format. To report such errors,  see  https://www.ker‐
107       nel.org/doc/man-pages/reporting_bugs.html .
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111IEEE/The Open Group                  2017                         SETREGID(3P)
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