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.\" 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.\" manual page may be incorrect or out-of-date.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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2007-06-10 18:18:04 +00:00
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.TH GETHOSTID 2 2007-06-15 "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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.SH DESCRIPTION
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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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The
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.I hostid
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argument is stored in the file
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.IR /etc/hostid .
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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 (2).
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.SH FILES
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.I /etc/hostid
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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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2007-06-10 18:08:27 +00:00
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.SH NOTES
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In the glibc implementation, if
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.BR gethostid ()
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cannot open
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.IR /etc/hostid ,
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then it obtains the host name using
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.BR gethostname (2),
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passes that host name 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 "SEE ALSO"
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.BR hostid (1),
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.BR gethostbyname (3)
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