man2/seteuid.2

   1 .\" Copyright (C) 2001 Andries Brouwer (aeb@cwi.nl)
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  23 .\" [should really be seteuid.3]
  24 .\" Modified, 27 May 2004, Michael Kerrisk <mtk-manpages@gmx.net>
  25 .\"     Added notes on capability requirements
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  27 .TH SETEGID 2 2007-07-26 "Linux" "Linux Programmer's Manual"
  28 .SH NAME
  29 seteuid, setegid \- set effective user or group ID
  30 .SH SYNOPSIS
  31 .B #include <sys/types.h>
  32 .br
  33 .B #include <unistd.h>
  34 .sp
  35 .BI "int seteuid(uid_t " euid );
  36 .br
  37 .BI "int setegid(gid_t " egid );
  38 .sp
  39 .in -4n
  40 Feature Test Macro Requirements for glibc (see
  41 .BR feature_test_macros (7)):
  42 .in
  43 .sp
  44 .ad l
  45 .BR seteuid (),
  46 .BR setegid ():
  47 _BSD_SOURCE || _POSIX_C_SOURCE\ >=\ 200112L || _XOPEN_SOURCE\ >=\ 600
  48 .ad b
  49 .SH DESCRIPTION
  50 .BR seteuid ()
  51 sets the effective user ID of the current process.
  52 Unprivileged user processes may only set the effective user ID to the
  53 real user ID, the effective user ID or the saved set-user-ID.
  54
  55 Precisely the same holds for
  56 .BR setegid ()
  57 with "group" instead of "user".
  58 .\" When
  59 .\" .I euid
  60 .\" equals \-1, nothing is changed.
  61 .SH "RETURN VALUE"
  62 On success, zero is returned.
  63 On error, \-1 is returned, and
  64 .I errno
  65 is set appropriately.
  66 .SH ERRORS
  67 .\" .TP
  68 .\" .B EINVAL
  69 .TP
  70 .B EPERM
  71 The current process is not privileged (Linux: does not have the
  72 .B CAP_SETUID
  73 capability in the case of
  74 .BR seteuid (),
  75 or the
  76 .B CAP_SETGID
  77 capability in the case of
  78 .BR setegid ())
  79 and
  80 .I euid
  81 (resp.
  82 .IR egid )
  83 is not the real user (group) ID, the effective user (group) ID,
  84 or the saved set-user-ID (saved set-group-ID).
  85 .SH "CONFORMING TO"
  86 4.3BSD, POSIX.1-2001.
  87 .SH NOTES
  88 Setting the effective user (group) ID to the
  89 saved set-user-ID (saved set-group-ID) is
  90 possible since Linux 1.1.37 (1.1.38).
  91 On an arbitrary system one should check _POSIX_SAVED_IDS.
  92 .LP
  93 Under libc4, libc5 and glibc 2.0
  94 .BI seteuid( euid )
  95 is equivalent to
  96 .BI setreuid(\-1, " euid" )
  97 and hence may change the saved set-user-ID.
  98 Under glibc2.1 it is equivalent to
  99 .BI setresuid(\-1, " euid" ", \-1)"
 100 and hence does not change the saved set-user-ID.
 101 Similar remarks hold for
 102 .BR setegid ().
 103 .SH "SEE ALSO"
 104 .BR geteuid (2),
 105 .BR setresuid (2),
 106 .BR setreuid (2),
 107 .BR setuid (2),
 108 .BR capabilities (7),
 109 .BR credentials (7)