Re: Dynamic hostname in rc.conf (for bhyve VMs)

On Sat, 10 Sep 2022 10:52:01 +0200
Guido Falsi <mad@madpilot.net> wrote:

> Hi,
> 
> Since rc.conf is just a shell script I'd like to be able to set hostname 
> dynamically.
> 
> This is bhyve related because what I'd like to do is pass an hostname to 
> VMs via the -e option to bhyveload(8), and then read it in rc.conf, 
> maybe via sysctl to set the hostname accordingly.
> 
> By the way I'm using vm-bhyve [1] to manage my VMs. its configuration 
> files are also shell scripts, so I was planning to hack some simple 
> logic there, host side, to derive the hostname from filesystem (useful 
> for cloned VMs).
> 
> Could not find any example or documentation about any step of this.
> 
> Is this even possible with current tools? I'm open to hacky solutions to 
> start with, then maybe refine them.
> 
> 
> I'm trying to do this because I'm using a local dnsmasq that exposes DNS 
> with the hostnames provided by VMs, but clones get the same naem as the 
> machien they're cloned from and mask those in this small internal DNS. 
> If each clone could provide it's different name it would be much better.
> 
> 
> Thanks in advance for any help/suggestions.
> 
> 
> [1] https://github.com/churchers/vm-bhyve
> 
> -- 
> Guido Falsi <mad@madpilot.net>
> 

IIUC, and if you obtain IP addresses of each VMs via DHCP,
just keeping hostname on rc.conf would be suffice.

/etc/rc.d/hostname has a functionality to get hostname by
hostname=`/bin/kenv dhcp.host-name`, meaning hostname is set using
what DHCP server supplied, if NOT in a jail.

See the script for details.

-- 
Tomoaki AOKI    <junchoon@dec.sakura.ne.jp>