Give a warning about using localhost in resolv.conf during install/upgrade

digininja · November 28, 2022, 5:15pm

My Pi-hole box is (was) using itself for name resolution.

I've just had an upgrade break as something in the process stopped the DNS server but the next step then tried to do something network related which failed as it couldn't get an IP address.

A quick discussion on twitter found you don't recommend pointing the host at itself as a resolver, this makes sense now I've had it mess things up, but was a pain at the time.

I'm suggesting you check /etc/resolv.conf to see if it is pointing at localhost and, if it is, then flag an alert in the installer to warn people to use something different. I agree not everyone will read it, but it may help some people.

PromoFaux · November 28, 2022, 5:21pm

To further expand on what I mentioned on Twitter:

There are only two places in the install script that stop pihole-FTL:

Here, when there is a detected upgrade for the pihole-FTL binary itself. We first download the binary, then stop and restart

github.com

pi-hole/pi-hole/blob/0034538794a3754ab532a53480da39d3fd13d7ed/automated install/basic-install.sh#L2208


      
          curl -sSL --fail "${url}/${binary}.sha1" -o "${binary}.sha1"
          
          
# If we downloaded binary file (as opposed to text),
          if sha1sum --status --quiet -c "${binary}".sha1; then
              printf "transferred... "
          
          
    # Before stopping FTL, we download the macvendor database
              curl -sSL "https://ftl.pi-hole.net/macvendor.db" -o "${PI_HOLE_CONFIG_DIR}/macvendor.db" || true
          
          
    # Stop pihole-FTL service if available
              stop_service pihole-FTL &> /dev/null
          
          
    # Install the new version with the correct permissions
              install -T -m 0755 "${binary}" /usr/bin/pihole-FTL
          
          
    # Move back into the original directory the user was in
              popd > /dev/null || { printf "Unable to return to original directory after FTL binary download.\\n"; return 1; }
          
          
    # Installed the FTL service
              printf "%b  %b %s\\n" "${OVER}" "${TICK}" "${str}"
              return 0

Here before making changes to some log file paths

github.com

pi-hole/pi-hole/blob/0034538794a3754ab532a53480da39d3fd13d7ed/automated install/basic-install.sh#L2672


      
          # Fixes a problem reported on Ubuntu 18.04 where trying to start
          # the service before enabling causes installer to exit
          enable_service pihole-FTL
          
          
# If this is an update from a previous Pi-hole installation
          # we need to move any existing `pihole*` logs from `/var/log` to `/var/log/pihole`
          # if /var/log/pihole.log is not a symlink (set during FTL startup) move the files
          # can be removed with Pi-hole v6.0
          # To be sure FTL is not running when we move the files we explicitly stop it here
          
          
stop_service pihole-FTL &> /dev/null
          
          
if [ ! -d /var/log/pihole/ ]; then
              mkdir -m 0755 /var/log/pihole/
          fi
          
          
# Special handling for pihole-FTL.log -> pihole/FTL.log
          if [ -f /var/log/pihole-FTL.log ] && [ ! -L /var/log/pihole-FTL.log ]; then
              # /var/log/pihole-FTL.log      -> /var/log/pihole/FTL.log
              # /var/log/pihole-FTL.log.1    -> /var/log/pihole/FTL.log.1
              # /var/log/pihole-FTL.log.2.gz -> /var/log/pihole/FTL.log.2.gz

Before finally starting it again here

github.com

pi-hole/pi-hole/blob/0034538794a3754ab532a53480da39d3fd13d7ed/automated install/basic-install.sh#L2694


      
              # /var/log/pihole-FTL.log.4.gz -> /var/log/pihole/FTL.log.4.gz
              # /var/log/pihole-FTL.log.5.gz -> /var/log/pihole/FTL.log.5.gz
              for f in /var/log/pihole-FTL.log*; do mv "$f" "$( sed "s/pihole-/pihole\//" <<< "$f")"; done
          fi
          
          
# Remaining log files
          if [ -f /var/log/pihole.log ] && [ ! -L /var/log/pihole.log ]; then
              mv /var/log/pihole*.* /var/log/pihole/ 2>/dev/null
          fi
          
          
restart_service pihole-FTL
          
          
# Download and compile the aggregated block list
          runGravity
          
          
# Update local and remote versions via updatechecker
          /opt/pihole/updatecheck.sh
          
          
if [[ "${useUpdateVars}" == false ]]; then
              displayFinalMessage "${pw}"
          fi

Between stopping and starting pihole-FTL again, there doesn't appear to be anywhere that needs to do a DNS lookup - so I am unsure where exactly it would have fallen over

digininja · November 30, 2022, 12:14pm

Unfortunately I fixed it without taking a screenshot so can't say where it failed. It was definitely trying to do something network related, I remember seeing the lookup failure error.

PromoFaux · November 30, 2022, 5:21pm

Yeah, absolutely. Like I said on Twitter - I'm not saying it can't happen - I just can't currently see where it might

system · May 29, 2023, 5:21pm

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