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
This normally resembles the Internet address for the local
machine, as returned by
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
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 host ID.
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.
In the glibc implementation, the
is stored in the file
(In glibc versions before 2.2, the file
In the glibc implementation, if
cannot open the file containing the host ID,
then it obtains the hostname using
passes that hostname to
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.