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Arseni Mourzenko
Asked: 2015-05-14 15:22:25 +0800 CST

How to prevent the deployment process from accessing DNS server?

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I noticed that when deploying a virtual machine while using a preseed, the host name specified in the preseed is ignored and the one from DNS server is used instead.

Detailed description

The Ubuntu Server machine is deployed using:

virt-install \
    --name custom-name \
    --initrd-inject /some-path/preseed.cfg \
    --extra-args "preseed/file=preseed.cfg" \
    ...

The preseed file contains, among others, the following lines (notice the custom-name value in the second line):

...
d-i netcfg/disable_dhcp boolean true
...
d-i netcfg/get_hostname string custom-name
d-i netcfg/get_domain string pelicandd.com
d-i netcfg/get_ipaddress string 192.168.1.35
...

On the other hand, DNS server contains both the A record:

demo    IN A       192.168.1.35

as well as the PTR record:

35      IN  PTR     demo.example.com.

Once the machine is created, it appears that /etc/hostname contains:

demo

and that /etc/hosts contains:

127.0.0.1       localhost
192.168.1.35    demo.example.com     demo

Question

I'm not particularly happy with the fact that the deployment process accesses the DNS server to get the information. Not only does it take time, but in some circumstances, the DNS server can be down (such as the case where it's the DNS server itself which is being deployed).

What should I specify in the preseed to prevent the installer from accessing DNS to retrieve information which is already available in the preseed?

preseed

1 Answers

  1. RTFM helped. From Debian's preseed example:

    # Any hostname and domain names assigned from dhcp take precedence over
# values set here. However, setting the values still prevents the questions
# from being shown, even if values come from dhcp.
d-i netcfg/get_hostname string unassigned-hostname
d-i netcfg/get_domain string unassigned-domain

# If you want to force a hostname, regardless of what either the DHCP
# server returns or what the reverse DNS entry for the IP is, uncomment
# and adjust the following line.
#d-i netcfg/hostname string somehost

    Which means that netcfg/get_hostname is irrelevant: its only purpose is to prevent the installer from asking the question in the first place.

    Indeed, when I set the value of netcfg/hostname, both /etc/hostname and /etc/hosts contain the values specified in the preseed, ignoring the DNS PTR record.

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