Re: [Astlinux-devel] When does DNS come up ?

[Lonnie A. <li...@lo...>]

> On Dec 19, 2020, at 7:54 AM, David Kerr <da...@ke...> wrote:
> 
> Can anyone tell me when DNS comes up during the boot process?  I am doing a host lookup within my firewall custom rules script $(host -t A $fqdn) and it appears to get no IP address when the firewall is setup during boot, but works fine if I do a firewall restart after the system has booted up.
> 
> Thanks

Hi David,

The order of the startup "Snn*" script symlinks are:

pbx3 ~ # cd /etc/runlevels/default/

pbx3 ~ # ls -l S*
...
lrwxrwxrwx    1 root     root            20 Dec 16 21:34 S03network -> ../../init.d/network
lrwxrwxrwx    1 root     root            19 Dec 16 21:34 S04elocal -> ../../init.d/elocal
lrwxrwxrwx    1 root     root            21 Dec 16 21:34 S05watchdog -> ../../init.d/watchdog
lrwxrwxrwx    1 root     root            22 Dec 16 21:34 S06lmsensors -> ../../init.d/lmsensors
lrwxrwxrwx    1 root     root            19 Dec 16 21:34 S08msmtpd -> ../../init.d/msmtpd
lrwxrwxrwx    1 root     root            18 Dec 16 21:34 S09crond -> ../../init.d/crond
lrwxrwxrwx    1 root     root            21 Dec 16 21:34 S10iptables -> ../../init.d/iptables
lrwxrwxrwx    1 root     root            23 Dec 16 21:34 S11netsyslogd -> ../../init.d/netsyslogd
lrwxrwxrwx    1 root     root            18 Dec 16 21:34 S11snmpd -> ../../init.d/snmpd
lrwxrwxrwx    1 root     root            23 Dec 16 21:34 S12keepalived -> ../../init.d/keepalived
lrwxrwxrwx    1 root     root            21 Dec 16 21:34 S18dnscrypt -> ../../init.d/dnscrypt
lrwxrwxrwx    1 root     root            20 Dec 16 21:34 S18unbound -> ../../init.d/unbound
lrwxrwxrwx    1 root     root            20 Dec 16 21:34 S20dnsmasq -> ../../init.d/dnsmasq
...

So the firewall starts at S10, and DNS starts at S20.

If you want to keep the $(host -t A $fqdn) in the firewall custom-rules, you could spawn a background sub-shell, something like:
https://github.com/astlinux-project/astlinux/blob/c3ff8beba28533487c65d77e9ec2d54dd9facc3b/package/openssh/sshd.init#L144

Off the top of my head , untested...
--
fqdn="example.com"
(
  cnt=6
  while [ $cnt -gt 0 ]; do
    cnt=$((cnt - 1))
    sleep 10

    A="$(host -t A $fqdn | sed -n -r -e 's#^.* has address ([0-9.]+)$#\1#p')"
    if [ -n "$A" ]; then
      ## use $A example ##
      echo "$A" > /tmp/test
      exit
    fi
  done
) >/dev/null 2>&1 &
--

Adjust the retry 'cnt' and sleep delay to your liking.

Lonnie