hostname curiosity [SOLVED] ...but curioser and curioser

[Steve]

---- "Mikkel L. Ellertson" <mikkel at infinity-ltd.com> wrote: 
> Steve wrote:
> > 
> > Cool! Adding 
> > 
> > DHCP_HOSTNAME=yes
> > 
> > to /etc/sysconfig/network-scripts/ifcfg-eth0 seems to have done
> > the trick. Now there is a longer pause during booting when it gets
> > to the Setting up eth0...[OK] line so I'm guessing it is waiting a
> > little longer to get an answer from the dhcp server.
> > Btw, where are the docs for the ifcfg-eth0 file syntax? There is
> > no man page for it.
> > 
> > Thanks
> > Steve
> > 
> /usr/share/doc/initscripts-8.86/sysconfig.txt

Interesting! 
First, I think the entry  for PERSISTENT_DHCLIENT option may explain what was happenning:

"Without this option, or if it is 'no'/'0', and BOOTPROTO=dhcp, [and this was set]
      dhclient is run for the interface in "one-shot" mode; if the 
      dhcp server does not respond for a configurable timeout, then
      dhclient exits and the interface is not brought up - 
      the '-1' option is given to dhclient.
      If PERSISTENT_DHCLIENT=yes, then dhclient will keep on trying
      to contact the dhcp server when it does not respond - no '-1'
      option is given to dhclient. Note: this disables the automatic
      checking for the presence of a link before starting dhclient."

I didn't have PERSISTENT_DHCLIENT in the configuration file so it would seem that the server did not respond in time when the machine was cold booted which explains why the hostname was not set but this also says that the interface is not brought up and yet it was.

The second thing is that there is no DHCP_HOSTNAME option listed in the  /usr/share/doc/initscripts-8.76.4/sysconfig.txt and yet it DHCP_HOSTNAME="yes" seems to work evem though PERSISTENT_DHCLIENT is still not set.

The third thing is that something is creating a /etc/dhclient-eth0.conf file at boot time that contains this line:

send host-name "yes";  # temporary RHL ifup addition

Obviously, my host name is not "yes" so this must be some special, undocumented use of send host-name that make the dhcp client get the hostname from the server.

Steve