dhcpcd-discuss

Hi Mark

On 20/04/2020 02:33, Mark Davies wrote:
> Hi,
>     I've been meaning to report this for a while:
>
> ArchLinux running dhcpcd-8.1.2 (but also happened in older versions and
> looks like may still happen in 9.0.1).
>
> Machines getting config, including hostname, via ipv4 dhcp (so running
> the 30-hostname hook) and getting ipv6 addressing via slaac.
>
> The hostname is successfully set on receipt of the dhcp packets, but
> then is reset to "localhost" each time a routeradvertisment packet is
> received.
>
> The following patch to hooks/30-hostname fixes the issue for me.
>
> --- dhcpcd-hooks/30-hostname    2019-11-15 05:34:16.000000000 +1300
> +++ dhcpcd-hooks/30-hostname    2019-12-11 10:40:47.935238981 +1300
> @@ -156,6 +156,6 @@
>          ;;
>   esac
>
> -if $if_up; then
> +if $if_up && [ "$reason" != ROUTERADVERT ]; then
>          set_hostname
>   fi

I don't understand how this can happen.
Look here:
https://roy.marples.name/cgit/dhcpcd.git/tree/hooks/30-hostname.in#n63

need_hostname decides if we want to set a hostname or not, using these rules:
1) Is the hostname a default hostname? If so, return 0
2) Is user variable force_hostname YES or TRUE? If so, return 0
3) Does the current hostname match the old hostname from the DHCP lease? If so, 
return 0
4) Return non zero.

Assuming you start with a valid hostname then the only way the 30-hostname 
script can clobber the hostname is if force_hostname is true.

If this is correct, does this patch work instead?

diff --git a/hooks/30-hostname.in b/hooks/30-hostname.in
index 579c73d3..6dc1b4f5 100644
--- a/hooks/30-hostname.in
+++ b/hooks/30-hostname.in
@@ -67,7 +67,9 @@ need_hostname()
        is_default_hostname "$hostname" && return 0

        case "$force_hostname" in
-       [Yy][Ee][Ss]|[Tt][Rr][Uu][Ee]|1) return 0;;
+       [Yy][Ee][Ss]|[Tt][Rr][Uu][Ee]|1)
+               [ -n "$new_fqdn" ] || [ -n "$new_host_name" ]
+               return $?;;
        esac

        if [ -n "$old_fqdn" ]; then


If this does not work, could you put set -x before if $if_up; then
and set +x after the if block and post back the output.

Thanks

Roy