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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | ATTRIBUTES | CONFORMING TO | NOTES | BUGS | SEE ALSO | COLOPHON |
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GETHOSTID(3) Linux Programmer's Manual GETHOSTID(3)
gethostid, sethostid - get or set the unique identifier of the cur‐
rent host
#include <unistd.h>
long gethostid(void);
int sethostid(long hostid);
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
gethostid():
_BSD_SOURCE || _XOPEN_SOURCE >= 500
sethostid():
Since glibc 2.21:
_DEFAULT_SOURCE
In glibc 2.19 and 2.20:
_DEFAULT_SOURCE || (_XOPEN_SOURCE && _XOPEN_SOURCE < 500)
Up to and including glibc 2.19:
_BSD_SOURCE || (_XOPEN_SOURCE && _XOPEN_SOURCE < 500)
gethostid() and 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.
The sethostid() call is restricted to the superuser.
gethostid() returns the 32-bit identifier for the current host as set
by sethostid().
On success, sethostid() returns 0; on error, -1 is returned, and
errno is set to indicate the error.
sethostid() can fail with the following errors:
EACCES The caller did not have permission to write to the file used
to store the host ID.
EPERM The calling process'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).
┌────────────┬───────────────┬───────────────────────────┐
│Interface │ Attribute │ Value │
├────────────┼───────────────┼───────────────────────────┤
│gethostid() │ Thread safety │ MT-Safe hostid env locale │
├────────────┼───────────────┼───────────────────────────┤
│sethostid() │ Thread safety │ MT-Unsafe const:hostid │
└────────────┴───────────────┴───────────────────────────┘
4.2BSD; these functions were dropped in 4.4BSD. SVr4 includes
gethostid() but not sethostid().
POSIX.1-2001 and POSIX.1-2008 specify gethostid() but not
sethostid().
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's IPv4 address, and returns a value obtained by
bit-twiddling the IPv4 address. (This value may not be unique.)
It is impossible to ensure that the identifier is globally unique.
hostid(1), gethostbyname(3)
This page is part of release 4.15 of the Linux man-pages project. A
description of the project, information about reporting bugs, and the
latest version of this page, can be found at
https://www.kernel.org/doc/man-pages/.
Linux 2017-09-15 GETHOSTID(3)
Pages that refer to this page: machine-id(5), attributes(7)
Copyright and license for this manual page
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