gethostid, sethostid - get or set the unique identifier of the current host
int sethostid(long hostid);
Feature Test Macro Requirements for glibc (see feature_test_macros
_XOPEN_SOURCE >= 500
Since glibc 2.21:
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)
() 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
(3), and thus usually never needs to be set.
() call is restricted to the superuser.
() returns the 32-bit identifier for the current host as set by
On success, sethostid
() returns 0; on error, -1 is returned, and
is set to indicate the error.
() can fail with the following errors:
- The caller did not have permission to write to the file used to store the
- 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
||MT-Safe hostid env locale
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
In the glibc implementation, the hostid
is stored in the file
. (In glibc versions before 2.2, the file
In the glibc implementation, if gethostid
() cannot open the file
containing the host ID, then it obtains the hostname using
(2), passes that hostname to gethostbyname_r
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.