Section (3) gethostid
gethostid, sethostid — get or set the unique identifier of the current host
sethostid() respectively get or set a
unique 32-bit identifier for the current machine. The 32-bit
identifier is intended to be unique among all UNIX systems in
existence. This normally resembles the Internet address for
the local machine, as returned by gethostbyname(3), and thus
usually never needs to be set.
sethostid() call is
restricted to the superuser.
gethostid() returns the
32-bit identifier for the current host as set by
returns 0; on error, −1 is returned, and
errno is set to indicate the error.
sethostid() can fail with
the following errors:
The caller did not have permission to write to the file used to store the host ID.
The calling process_zsingle_quotesz_s effective user or group ID is not the same as its corresponding real ID.
For an explanation of the terms used in this section, see attributes(7).
||Thread safety||MT-Safe hostid env locale|
||Thread safety||MT-Unsafe const:hostid|
4.2BSD; these functions were dropped in 4.4BSD. SVr4
gethostid() but not
POSIX.1-2001 and POSIX.1-2008 specify
gethostid() but not
In the glibc implementation, the
hostid is stored in the file
/etc/hostid. (In glibc versions
before 2.2, the file
/var/adm/hostid was used.)
In the glibc implementation, if
gethostid() cannot open the file containing
the host ID, then it obtains the hostname using gethostname(2), passes that
hostname to gethostbyname_r(3) in order
to obtain the host_zsingle_quotesz_s IPv4 address, and returns a value
obtained by bit-twiddling the IPv4 address. (This value may
not be unique.)
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and the latest version of this page, can be found at
Copyright 1993 Rickard E. Faith (faithcs.unc.edu)
Updated with additions from Mitchum DSouza <m.dsouzamrc-apu.cam.ac.uk>
Portions Copyright 1993 Mitchum DSouza <m.dsouzamrc-apu.cam.ac.uk>
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Modified Tue Oct 22 00:22:35 EDT 1996 by Eric S. Raymond <esrthyrsus.com>