[NTLUG:Discuss] Host ID

[Steve Baker]

OK - I figured out what the 'hostid' command does.

It takes the Internet address of the machine (not the 6 byte NIC address)
and swizzles the bytes around.

On my machine for example:

 > hostid -v
Hostid is 2831155970 (0xa8c00302)

...well, that machine is 192.168.2.3 on my local network.  Converting
those four numbers to Hex yields:

   C0 A8 02 03

...which is an anagram of...

   A8 C0 03 02           (Network order?)

...which is the hex output from hostid.

So, using 'hostid' to register software isn't a good idea since anyone
can give their machine pretty much any number they like once it's on
a private network.

This probably explains why so many of us have identical hostid numbers.

In fact, you can set your hostid to be anything you like. The 'man' page
for hostid (Under SuSE 7.2) says:

   SYNTAX
        hostid [-v] [decimal-id]

   DESCRIPTION
        The  hostid  command  prints the current host id number in
        hexadecimal and both decimal and hexadecimal in  parenthe­
        sis  if  the  -v  option  is given.  This numeric value is
        expected to be unique across all hosts and is normally set
        to resemble the host's Internet address.

        Only  the super-user can set the hostid by giving an argu­
        ment. This value is stored in  the  file  /etc/hostid  and
        need only be performed once.

----------------------------- Steve Baker -------------------------------
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