mirror of https://github.com/mkerrisk/man-pages
127 lines
3.7 KiB
Groff
127 lines
3.7 KiB
Groff
.\" Hey Emacs! This file is -*- nroff -*- source.
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.\"
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.\" Copyright 1993 Rickard E. Faith (faith@cs.unc.edu)
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.\"
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.\" Permission is granted to make and distribute verbatim copies of this
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.\" manual provided the copyright notice and this permission notice are
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.\" preserved on all copies.
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.\"
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.\" Permission is granted to copy and distribute modified versions of this
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.\" manual under the conditions for verbatim copying, provided that the
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.\" entire resulting derived work is distributed under the terms of a
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.\" permission notice identical to this one.
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.\"
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.\" Since the Linux kernel and libraries are constantly changing, this
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.\" manual page may be incorrect or out-of-date. The author(s) assume no
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.\" responsibility for errors or omissions, or for damages resulting from
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.\" the use of the information contained herein. The author(s) may not
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.\" have taken the same level of care in the production of this manual,
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.\" which is licensed free of charge, as they might when working
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.\" professionally.
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.\"
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.\" Formatted or processed versions of this manual, if unaccompanied by
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.\" the source, must acknowledge the copyright and authors of this work.
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.\"
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.\" Updated with additions from Mitchum DSouza <m.dsouza@mrc-apu.cam.ac.uk>
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.\" Portions Copyright 1993 Mitchum DSouza <m.dsouza@mrc-apu.cam.ac.uk>
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.\"
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.\" Modified Tue Oct 22 00:22:35 EDT 1996 by Eric S. Raymond <esr@thyrsus.com>
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.TH GETHOSTID 3 2010-09-20 "Linux" "Linux Programmer's Manual"
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.SH NAME
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gethostid, sethostid \- get or set the unique identifier of the current host
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.SH SYNOPSIS
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.B #include <unistd.h>
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.sp
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.B long gethostid(void);
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.br
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.BI "int sethostid(long " hostid );
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.sp
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.in -4n
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Feature Test Macro Requirements for glibc (see
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.BR feature_test_macros (7)):
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.in
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.sp
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.ad l
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.br
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.BR gethostid ():
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.RS 4
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_BSD_SOURCE || _XOPEN_SOURCE\ >=\ 500 ||
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_XOPEN_SOURCE\ &&\ _XOPEN_SOURCE_EXTENDED
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.RE
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.BR sethostid ():
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.RS 4
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_BSD_SOURCE || (_XOPEN_SOURCE && _XOPEN_SOURCE\ <\ 500)
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.RE
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.ad b
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.SH DESCRIPTION
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.BR gethostid ()
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and
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.BR sethostid ()
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respectively get or set a unique 32-bit identifier for the current machine.
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The 32-bit identifier is intended to be unique among all UNIX systems in
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existence.
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This normally resembles the Internet address for the local
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machine, as returned by
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.BR gethostbyname (3),
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and thus usually never needs to be set.
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The
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.BR sethostid ()
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call is restricted to the superuser.
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.SH "RETURN VALUE"
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.BR gethostid ()
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returns the 32-bit identifier for the current host as set by
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.BR sethostid ().
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On success,
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.BR sethostid ()
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returns 0; on error, \-1 is returned, and
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.I errno
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is set to indicate the error.
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.SH ERRORS
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.BR sethostid ()
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can fail with the following errors:
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.TP
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.B EACCES
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The caller did not have permission to write to the file used
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to store the host ID.
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.TP
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.B EPERM
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The calling process's effective user or group ID is not the same
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as its corresponding real ID.
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.SH "CONFORMING TO"
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4.2BSD; these functions were dropped in 4.4BSD.
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SVr4 includes
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.BR gethostid ()
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but not
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.BR sethostid ().
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POSIX.1-2001 specifies
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.BR gethostid ()
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but not
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.BR sethostid ().
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.SH NOTES
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In the glibc implementation, the
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.I hostid
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is stored in the file
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.IR /etc/hostid .
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(In glibc versions before 2.2, the file
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.I /var/adm/hostid
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was used.)
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.\" libc5 used /etc/hostid; libc4 didn't have these functions
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In the glibc implementation, if
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.BR gethostid ()
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cannot open the file containing the host ID,
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then it obtains the hostname using
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.BR gethostname (2),
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passes that hostname to
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.BR gethostbyname_r (3)
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in order to obtain the host's IPv4 address,
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and returns a value obtained by bit-twiddling the IPv4 address.
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(This value may not be unique.)
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.SH BUGS
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It is impossible to ensure that the identifier is globally unique.
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.SH "SEE ALSO"
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.BR hostid (1),
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.BR gethostbyname (3)
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