| NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | CONFORMING TO | NOTES | BUGS | SEE ALSO | COLOPHON | The Linux Programming Interface |
GETHOSTID(3) Linux Programmer's Manual GETHOSTID(3)
gethostid, sethostid - get or set the unique identifier of the current 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 ||
_XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED
sethostid():
_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.
4.2BSD; these functions were dropped in 4.4BSD. SVr4 includes gethostid() but
not sethostid(). POSIX.1-2001 specifies 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 3.32 of the Linux man-pages project. A
description of the project, and information about reporting bugs, can be found
at http://www.kernel.org/doc/man-pages/.
Linux 2010-09-20 GETHOSTID(3)
HTML rendering created 2010-12-03 by Michael Kerrisk, author of The Linux Programming Interface