Feuerfest

For some reasons ISSO stopped working after I upgraded to Debian Trixie. Steps which weren't necessary when I first wrote my post Integrating Isso into Bludit via Apache2 and WSGI.

Take this post as an addition to the previous one.

Troubleshooting steps for Debian Trixie

ModuleNotFoundError: No module named 'pkg_resources'

This one was solved with an pip install setuptools. Despite being already installed and shown as installed when pip list is executed.

ModuleNotFoundError: No module named '_cffi_backend'

This one still baffles me. pip list shows the cffi module as being installed. However under Debian the package python3-cffi-backend must be installed for me. I think that I maybe hadn't all needed ffi packages installed, so the compiled /opt/your-venv-here/lib/python3.13/site-packages/_cffi_backend.cpython-313-x86_64-linux-gnu.so isn't fully working. Have to investigate.

If these two things are taken care of ISSO works fine under Debian Trixie.

Conclusion

All in all I suspect that I did get those errors as I did an in-place dist-upgrade from bullseye to bookworm to trixie on one afternoon. No fresh re-install as I currently lack the time for this.

The following log message would only sporadically be logged on my Pi-hole. Not every hour, and not even every day. Just... sometimes. When the stars aligned... When, 52 years ago, Monday fell on a full moon and a 12th-generation carpenter was born... You get the idea.  😄

The error message was:

"No valid NTP replies received, check server and network connectivity"

Strange. NTP works. Despite Pi-hole sometimes fancy otherwise.

Inspecting the Pi-hole configuration

pihole-FTL returned the following NTP configuration:

user@host:~$ pihole-FTL --config ntp
ntp.ipv4.active = true
ntp.ipv4.address =
ntp.ipv6.active = true
ntp.ipv6.address =
ntp.sync.active = true
ntp.sync.server = 1.de.pool.ntp.org
ntp.sync.interval = 3600
ntp.sync.count = 8
ntp.sync.rtc.set = false
ntp.sync.rtc.device =
ntp.sync.rtc.utc = true

That looked good to me.

It was here that I had my suspicions: Wait, does the NTP Pool Project already offer IPv6? I have never knowingly used public NTP pools with IPv6. In customer networks, NTP servers are usually only reachable via IPv4. I don't have an NTP server in my home network. Sadly, many services are still not IPv6 ready.

Some companies even remove IPv6 support, like DigiCert (a commercial certificate authority!), who removed IPv6 support when they switched to a new CDN provider. This left me speechless. Read https://knowledge.digicert.com/alerts/digicert-certificate-status-ip-address if you want to know more.

NTP & IPv6? Only with pools that start with a 2

A short search for IPv6 support in NTP-Pools and https://www.ntppool.org/en/use.html provided the answer:

Please also note that the system currently only provides IPv6 addresses for a zone in addition to IPv4 addresses if the zone name is prefixed by the number 2, e.g. 2.pool.ntp.org (provided there are any IPv6 NTP servers in the respective zone). Zone names not prefixed by a number, or prefixed with any of 0, 1 or 3, currently provide IPv4 addresses only.

It turns out that the problem lies in my dual-stack setup, since I use IPv4 and IPv6 in parallel. Or rather... It's with the NTP pools. I checked with dig to see if any AAAA records were returned for 1.de.pool.ntp.org. The pool I was using.

dig aaaa 1.de.pool.ntp.org returns no AAAA-Records.

user@host:~$ dig aaaa 1.de.pool.ntp.org

; <<>> DiG 9.18.33-1~deb12u2-Debian <<>> aaaa 1.de.pool.ntp.org
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 43230
;; flags: qr rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 1, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 1232
; EDE: 3 (Stale Answer)
;; QUESTION SECTION:
;1.de.pool.ntp.org.             IN      AAAA

;; AUTHORITY SECTION:
pool.ntp.org.           0       IN      SOA     d.ntpns.org. hostmaster.pool.ntp.org. 1749216969 5400 5400 1209600 3600

;; Query time: 0 msec
;; SERVER: 127.0.0.1#53(127.0.0.1) (UDP)
;; WHEN: Fri Jun 06 16:10:31 CEST 2025
;; MSG SIZE  rcvd: 134

And surely enough a dig aaaa 2.de.pool.ntp.org returns AAAA-Records.

user@host:~$ dig aaaa 2.de.pool.ntp.org

; <<>> DiG 9.18.33-1~deb12u2-Debian <<>> aaaa 2.de.pool.ntp.org
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 47906
;; flags: qr rd ra; QUERY: 1, ANSWER: 4, AUTHORITY: 0, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 1232
;; QUESTION SECTION:
;2.de.pool.ntp.org.             IN      AAAA

;; ANSWER SECTION:
2.de.pool.ntp.org.      130     IN      AAAA    2a0f:85c1:b73:62:123:123:123:123
2.de.pool.ntp.org.      130     IN      AAAA    2a01:239:2a6:d500::1
2.de.pool.ntp.org.      130     IN      AAAA    2606:4700:f1::1
2.de.pool.ntp.org.      130     IN      AAAA    2a01:4f8:141:282::5:1

;; Query time: 656 msec
;; SERVER: 127.0.0.1#53(127.0.0.1) (UDP)
;; WHEN: Fri Jun 06 16:33:32 CEST 2025
;; MSG SIZE  rcvd: 158

My new Pi-hole configuration

The fix was easy, just configure 2.de.pool.ntp.org instead of 1.de.pool.ntp.org. Done.

user@host:~$ pihole-FTL --config ntp
ntp.ipv4.active = true
ntp.ipv4.address =
ntp.ipv6.active = true
ntp.ipv6.address =
ntp.sync.active = true
ntp.sync.server = 2.de.pool.ntp.org
ntp.sync.interval = 3600
ntp.sync.count = 8
ntp.sync.rtc.set = false
ntp.sync.rtc.device =
ntp.sync.rtc.utc = true

Now my Pi-hole instances aren't running long enough to really verify that the error is gone but I suspect so.

Some weeks later: The error is gone. It didn't re-appear.

If you are instead searching for an explanation of the error code have a look at RFC 8914.

I noticed that the DNS resolution on my secondary Pi-hole instance wasn't working. host wouldn't resolve a single DNS name. As the /etc/resolv.conf included only the DNS servers running on localhost (127.0.0.1 and ::1) DNS resolution didn't work at all. Naturally I started looking at the Pi-hole logfiles.

/var/log/pihole/pihole.log would log this for all domains.

Jun  4 00:02:54 dnsmasq[4323]: query 1.de.pool.ntp.org from 127.0.0.1
Jun  4 00:02:54 dnsmasq[4323]: forwarded 1.de.pool.ntp.org to 127.0.0.1#5335
Jun  4 00:02:54 dnsmasq[4323]: forwarded 1.de.pool.ntp.org to ::1#5335
Jun  4 00:02:54 dnsmasq[4323]: validation 1.de.pool.ntp.org is BOGUS
Jun  4 00:02:54 dnsmasq[4323]: reply error is SERVFAIL (EDE: DNSSEC bogus)

Ok that was a first hint. I checked /var/log/pihole/FTL.log and there would be this message repeated all over again.

2025-06-03 00:02:52.505 CEST [841/T22762] ERROR: Error NTP client: Cannot resolve NTP server address: Try again
2025-06-03 00:02:52.509 CEST [841/T22762] INFO: Local time is too inaccurate, retrying in 600 seconds before launching NTP server

NTP is not the culprit

I checked the local time and it matched the time on the primary Pi-hole instance. Strange. I even opened https://uhr.ptb.de/ which is the official time clock for Germany (yes, per law). And it matched to the second. timedatectl would also print the correct time for both UTC and CEST and state that the system clock is synchronized.

root@host:~# timedatectl
               Local time: Wed 2025-06-04 00:51:07 CEST
           Universal time: Tue 2025-06-03 22:51:07 UTC
                 RTC time: n/a
                Time zone: Europe/Berlin (CEST, +0200)
System clock synchronized: yes
              NTP service: active
          RTC in local TZ: no

What the heck was going on?

Unbound leftovers

I googled "EDE: DNSSEC bogus" dnsmasq and found the solution in https://www.reddit.com/r/pihole/comments/zsrjzn/2_piholes_with_unbound_breaking_dns/.

Turns out I forgot to execute two critical steps.

1. I didn't delete /etc/unbound/unbound.conf.d/resolvconf_resolvers.conf
2. I didn't comment out the line starting with unbound_conf= in /etc/resolvconf.conf

Or they came back, when I updated that Raspberry from Debian Bullseye to Bookworm today. Anyway after doing these two steps and restarting Unbound it now works flawlessly.

And I learned which files are not kept in sync by nebula-sync. 😉

I run a Pi-hole installation on each of my Raspberry 3 & 4. As I do like to keep my DNS queries as much under my control as I can, I also installed Unbound to serve as recursive DNS server. This way all DNS queries will be handled by my Raspberry Pis.

Pi-hole is already installed using one of the following methods: https://github.com/pi-hole/pi-hole/#one-step-automated-install. If you don't have that done yet, do it first.

There is a good guide at the Pi-hole website which I will basically following.

https://docs.pi-hole.net/guides/dns/unbound/

root@host:~# apt install unbound

Regarding the configuration file I go with the one in the guide. However as I did have some problems in that past I needed to troubleshoot I include the following lines regarding loglevels and verbosity:

root@host:~# head /etc/unbound/unbound.conf.d/pihole.conf
server:
    # If no logfile is specified, syslog is used
    logfile: "/var/log/unbound/unbound.log"
    val-log-level: 2
    # Default is 1
    #verbosity: 4
    verbosity: 1

    interface: 127.0.0.1
    port: 5335
root@host:~# 

You can add that if you want but it's not needed to make Unbound work.

Next the guide tells us to download the root hints. A file maintained by Internic which contains information about the 13 DNS root name servers. Under Debian we don't need to download the named.root file from Internic as shown in the guide. Debian has its own package for that: dns-root-data.

It no only contains information about the 13 DNS root name servers but also the needed DNSSEC keys (also called root trust anchors). And together with unattended-upgrades we even automate updating that. Saving us the creation of a Cronjob or systemd timer.

root@host:~# apt install dns-root-data

In order for Unbound to have a directory and logfile to write into we need to create that:

root@host:~# mkdir -p /var/log/unbound
root@host:~# touch /var/log/unbound/unbound.log
root@host:~# chown unbound /var/log/unbound/unbound.log

As we are running under Debian we now need to tweak the Unbound config a little bit. Else we will get problems with DNSSEC. For this we are deleting a Debian generated file from Unbound and comment out the unbound_conf= line in /etc/resolvconf.conf so that it isn't included anymore.

root@host:~# sed -Ei 's/^unbound_conf=/#unbound_conf=/' /etc/resolvconf.conf
root@host:~# rm /etc/unbound/unbound.conf.d/resolvconf_resolvers.conf

Now all that is left is restarting Unbound.

root@host:~# systemctl restart unbound.service

Testing DNS resolution:

root@host:~# dig pi-hole.net @127.0.0.1 -p 5335

; <<>> DiG 9.18.33-1~deb12u2-Raspbian <<>> pi-hole.net @127.0.0.1 -p 5335
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 46191
;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 1232
;; QUESTION SECTION:
;pi-hole.net.                   IN      A

;; ANSWER SECTION:
pi-hole.net.            300     IN      A       3.18.136.52

;; Query time: 169 msec
;; SERVER: 127.0.0.1#5335(127.0.0.1) (UDP)
;; WHEN: Sun May 25 18:21:25 CEST 2025
;; MSG SIZE  rcvd: 56

And to verify & falsify DNSSEC. This request must return an A-Record for dnssec.works.

root@host:~# dig dnssec.works @127.0.0.1 -p 5335

; <<>> DiG 9.18.33-1~deb12u2-Raspbian <<>> dnssec.works @127.0.0.1 -p 5335
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 14076
;; flags: qr rd ra ad; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 1232
;; QUESTION SECTION:
;dnssec.works.                  IN      A

;; ANSWER SECTION:
dnssec.works.           3600    IN      A       46.23.92.212

;; Query time: 49 msec
;; SERVER: 127.0.0.1#5335(127.0.0.1) (UDP)
;; WHEN: Sun May 25 18:22:52 CEST 2025
;; MSG SIZE  rcvd: 57

This request will not result in an A-Record.

root@host:~# dig fail01.dnssec.works @127.0.0.1 -p 5335

; <<>> DiG 9.18.33-1~deb12u2-Raspbian <<>> fail01.dnssec.works @127.0.0.1 -p 5335
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: SERVFAIL, id: 1552
;; flags: qr rd ra; QUERY: 1, ANSWER: 0, AUTHORITY: 0, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 1232
;; QUESTION SECTION:
;fail01.dnssec.works.           IN      A

;; Query time: 19 msec
;; SERVER: 127.0.0.1#5335(127.0.0.1) (UDP)
;; WHEN: Sun May 25 18:23:41 CEST 2025
;; MSG SIZE  rcvd: 48

Now all that is left to connect our Pi-hole with Unbound. Logon to your Pi-hole website and navigate to Settings -> DNS. Expand the line Custom DNS servers and enter to IP and Port to our Unbound server. 127.0.0.1#5335 for IPv4 and ::1#5335 for IPv6. If you don't use one of these two just don't add the line. After that hit "Save & Apply" and we are done.

Creating a logrotate config for Unbound

Sadly Unbound still doesn't deliver a logrotate config with its package. Therefore I just copy & paste from my previous article Howto properly split all logfile content based on timestamps - and realizing my own fallacy.

root@host:~# cat /etc/logrotate.d/unbound
/var/log/unbound/unbound.log {
        monthly
        missingok
        rotate 12
        compress
        delaycompress
        notifempty
        sharedscripts
        create 644
        postrotate
                /usr/sbin/unbound-control log_reopen
        endscript
}

Troubleshooting

fail01.dnssec.works timed out

The host fail01.dnssec.works tends to not answer requests sometimes. Others noticed this too. dig will only show the following message:

root@host:~# dig fail01.dnssec.works @127.0.0.1 -p 5335
;; communications error to 127.0.0.1#5335: timed out
;; communications error to 127.0.0.1#5335: timed out
;; communications error to 127.0.0.1#5335: timed out

; <<>> DiG 9.18.33-1~deb12u2-Raspbian <<>> fail01.dnssec.works @127.0.0.1 -p 5335
;; global options: +cmd
;; no servers could be reached

If that is the case, just execute the command again. Usually it will work the second time. Or just wait a few minutes. Sometimes the line ;; communications error to 127.0.0.1#5335: timed out will be printed, but the dig query will work after that nonetheless.

Photo by Pixabay: https://www.pexels.com/photo/software-engineers-working-on-computers-256219/

During my series about unattended-upgrades (Part 1, Part 2) I noticed that a Debian Mirror I use was unresponsive for 22 days but I had nothing to notify me of this. As this also meant that unattended-upgrades didn't apply any patches I wanted a check for this which in turn will trigger unattended-upgrades when there are outstanding updates.

The problem

The monitoring-plugins provide the check_apt plugin. This is normally used to check for available packages. However, in the default configuration it doesn't execute an apt-get update as this requires root privileges. Personally I think the risk is worth the gain. As adding the -u parameter will execute an apt-get update and therefore check_apt will notify you when apt-get update finishes with a non-zero exit-code.

Take the following problem:

root@host:~# apt-get update
Hit:1 http://security.debian.org/debian-security bookworm-security InRelease
Hit:2 http://debian.tu-bs.de/debian bookworm InRelease
Get:3 http://debian.tu-bs.de/debian bookworm-updates InRelease [55.4 kB]
Reading package lists... Done
E: Release file for http://debian.tu-bs.de/debian/dists/bookworm-updates/InRelease is expired (invalid since 16d 0h 59min 33s). Updates for this repository will not be applied.

A mere check_apt wont notify you of any problems:

root@host:~# /usr/lib/nagios/plugins/check_apt
APT CRITICAL: 12 packages available for upgrade (12 critical updates). |available_upgrades=12;;;0 critical_updates=12;;;0

Making this go undetected.

Executed with the -u parameter however, we are notified of the problem:

root@host:~# /usr/lib/nagios/plugins/check_apt -u
'/usr/bin/apt-get -q update' exited with non-zero status.
APT CRITICAL: 12 packages available for upgrade (12 critical updates).  warnings detected, errors detected.|available_upgrades=12;;;0 critical_updates=12;;;0

The solution

Fixing this via Icinga is however a bit more complicated, as the standard apt CheckCommand from the Icinga Template Library (ITL) doesn't include the -u option and isn't prefixed to use sudo despite root privileges being needed. This can be checked here: https://github.com/Icinga/icinga2/blob/master/itl/command-plugins.conf#L2155 or in your local /usr/share/icinga2/include/command-icinga.conf if you happen to use Icinga.

The root cause is also the number one main problem I have with the check_apt CheckPlugin. check_apt is designed to actually install package updates when check_apt reports outstanding available updates. This however breaks the number one paradigm I have regarding monitoring systems: They should not modify the system on their own. And when they do, they should do it in the same way as it is normally done. check_apt breaks this.

Maybe that person should have read a blog article about unattended-upgrades prior to writting that plugin? 😜

Normally you utilize Event Commands for that type of scenario: "If service X is in state Y execute event command Z."

The CheckCommand check_apt_update

Therefore I recommend creating your own apt_update CheckCommand and using that.

object CheckCommand "check_apt_update" {
        command = [ "/usr/bin/sudo", + PluginDir + "/check_apt" ]

        arguments = {
                "-u" = {
                        description = "Perform an apt-get update"
                }
        }
}

Defining the service and configuring the EventCommand

Then in your service definition add a suitable event_command:

apply Service "apt repositories" to Host {
  import "hourly-service"

  check_command = "check_apt_update"

  enable_event_handler = true
  // Execute unattended-upgrades automatically if service goes critical
  event_command = "execute_unattended_upgrades"
  // For services which should be executed ON the host itself
  command_endpoint = host.vars.agent_endpoint

  assign where host.vars.distribution == "Debian"

}

Creating the EventCommand

And create the EventCommand like this:

object EventCommand "execute_unattended_upgrades" {
  command = "sudo /usr/bin/unattended-upgrades"
}

Necessary sudo rights

This requires a sudo config file for the icinga user executing that command. And the commands must be executable without the need for a TTY, hence we end up with the following:

root@host:~# cat /etc/sudoers.d/icinga2
# This line disables the need for a tty for sudo
#  else we will get all kind of "sudo: a password is required" errors
Defaults:icinga2 !requiretty

# sudo rights for Icinga2
icinga2  ALL=(ALL) NOPASSWD: /usr/bin/unattended-upgrades
icinga2  ALL=(ALL) NOPASSWD: /usr/bin/unattended-upgrade
icinga2  ALL=(ALL) NOPASSWD: /usr/bin/apt-get
icinga2  ALL=(ALL) NOPASSWD: /usr/lib/nagios/plugins/check_apt

Conclusion

This is now sufficient as I'm notified when something prevents APT from properly updating the package lists. APT itself takes care to validate the various entries inside the Release file and exits with a non-zero exit-code, so there is no need to put that logic inside of check_apt.

Setting up similar checks for other monitoring systems is of course also possible. In general raising an alarm when apt-get update throws an non-zero exit-code is a somewhat foolproof method.

Photo by Markus Winkler: https://www.pexels.com/photo/the-word-update-is-spelled-out-in-scrabble-tiles-18524143/

Preface

At the time of this writing Debian Bookworm is the stable release of Debian. It utilizes Systemd timers for all automation tasks such as the updating of the package lists and execution of the actual apt-get upgrade. Therefore we won't need to configure APT-Parameters in files like /etc/apt/apt.conf.d/02periodic. In fact some of these files don't even exist on my systems. Keep that in mind if you read this article along with others, who might do things differently - or for older/newer releases of Debian.

Part 1 where I talk about the basics and prerequisites of unattended-upgrades along with many questions you should have answered prior using it is here: Using and configuring unattended-upgrades under Debian Bookworm - Part 1: Preparations

Note: As it took me considerably longer than expected to write this post please ignore discrepances in timestamps and versions.

Installing unattended-upgrades - however it's (most likely) not active yet

Enough with theory, let's switch to the shell. The installation is rather easy, a simple apt-get install unattended-upgrades is enough. However if you run the installation in an interactive way like this unattended-upgrades isn't configured to run automatically. The file /etc/apt/apt.conf.d/20auto-upgrades is missing. So check if it is present!

Note: That's one reason why you want to set the environment variable export DEBIAN_FRONTEND=noninteractive prior to the installation in your Ansible Playbooks/Puppet Manifest/Runbooks/Scripts, etc. or execute an dpkg-reconfigure -f noninteractive unattended-upgrades after the installation. Of course placing the file also solves the problem.😉

If you want to re-configure unattended-upgrades manually execute: dpkg-reconfigure unattended-upgrades and select yes at the prompt. But I advise you not just do it right yet.

root@host:~# apt-get install unattended-upgrades
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
The following additional packages will be installed:
  gir1.2-glib-2.0 libgirepository-1.0-1 python3-dbus python3-distro-info python3-gi
Suggested packages:
  python-dbus-doc bsd-mailx default-mta | mail-transport-agent needrestart powermgmt-base
The following NEW packages will be installed:
  gir1.2-glib-2.0 libgirepository-1.0-1 python3-dbus python3-distro-info python3-gi unattended-upgrades
0 upgraded, 6 newly installed, 0 to remove and 50 not upgraded.
Need to get 645 kB of archives.
After this operation, 2,544 kB of additional disk space will be used.
Do you want to continue? [Y/n]
Get:1 http://debian.tu-bs.de/debian bookworm/main amd64 libgirepository-1.0-1 amd64 1.74.0-3 [101 kB]
Get:2 http://debian.tu-bs.de/debian bookworm/main amd64 gir1.2-glib-2.0 amd64 1.74.0-3 [159 kB]
Get:3 http://debian.tu-bs.de/debian bookworm/main amd64 python3-dbus amd64 1.3.2-4+b1 [95.1 kB]
Get:4 http://debian.tu-bs.de/debian bookworm/main amd64 python3-distro-info all 1.5+deb12u1 [6,772 B]
Get:5 http://debian.tu-bs.de/debian bookworm/main amd64 python3-gi amd64 3.42.2-3+b1 [219 kB]
Get:6 http://debian.tu-bs.de/debian bookworm/main amd64 unattended-upgrades all 2.9.1+nmu3 [63.3 kB]
Fetched 645 kB in 0s (1,618 kB/s)
Preconfiguring packages ...
Selecting previously unselected package libgirepository-1.0-1:amd64.
(Reading database ... 33397 files and directories currently installed.)
Preparing to unpack .../0-libgirepository-1.0-1_1.74.0-3_amd64.deb ...
Unpacking libgirepository-1.0-1:amd64 (1.74.0-3) ...
Selecting previously unselected package gir1.2-glib-2.0:amd64.
Preparing to unpack .../1-gir1.2-glib-2.0_1.74.0-3_amd64.deb ...
Unpacking gir1.2-glib-2.0:amd64 (1.74.0-3) ...
Selecting previously unselected package python3-dbus.
Preparing to unpack .../2-python3-dbus_1.3.2-4+b1_amd64.deb ...
Unpacking python3-dbus (1.3.2-4+b1) ...
Selecting previously unselected package python3-distro-info.
Preparing to unpack .../3-python3-distro-info_1.5+deb12u1_all.deb ...
Unpacking python3-distro-info (1.5+deb12u1) ...
Selecting previously unselected package python3-gi.
Preparing to unpack .../4-python3-gi_3.42.2-3+b1_amd64.deb ...
Unpacking python3-gi (3.42.2-3+b1) ...
Selecting previously unselected package unattended-upgrades.
Preparing to unpack .../5-unattended-upgrades_2.9.1+nmu3_all.deb ...
Unpacking unattended-upgrades (2.9.1+nmu3) ...
Setting up python3-dbus (1.3.2-4+b1) ...
Setting up libgirepository-1.0-1:amd64 (1.74.0-3) ...
Setting up python3-distro-info (1.5+deb12u1) ...
Setting up unattended-upgrades (2.9.1+nmu3) ...

Creating config file /etc/apt/apt.conf.d/50unattended-upgrades with new version
Created symlink /etc/systemd/system/multi-user.target.wants/unattended-upgrades.service → /lib/systemd/system/unattended-upgrades.service.
Synchronizing state of unattended-upgrades.service with SysV service script with /lib/systemd/systemd-sysv-install.
Executing: /lib/systemd/systemd-sysv-install enable unattended-upgrades
Setting up gir1.2-glib-2.0:amd64 (1.74.0-3) ...
Setting up python3-gi (3.42.2-3+b1) ...
Processing triggers for man-db (2.11.2-2) ...
Processing triggers for libc-bin (2.36-9+deb12u3) ...
root@host:~# 

After the installation we have a new Systemd service called unattended-upgrades.service however, if you think that stopping this service will disable unattended-upgrades you are mistaken. This unit-file solely exists to check if an unattended-upgrades run is in progress and ensure it isn't killed mid-process, for example, during a shutdown.

To disable unattended-upgrades we need to change the values in /etc/apt/apt.conf.d/20auto-upgrades to zero. But as written above: This file currently isn't present in our system yet.

root@host:~# ls -lach /etc/apt/apt.conf.d/20auto-upgrades
ls: cannot access '/etc/apt/apt.conf.d/20auto-upgrades': No such file or directory

However, as we want to have a look at the internals first, we do not fix this yet. Instead, let us have a look at the relevant Systemd unit and timer-files.

The Systemd unit and timer files unattended-upgrades relies upon

An systemctl list-timers --all will show you all in-/active timer files on our system along with the unit-file which is triggered by the timer. On every Debian system utilizing Systemd you will most likely have the following unit and timers files per-default. Even when unattended-upgrades is not installed.

root@host:~# systemctl list-timers --all
NEXT                         LEFT          LAST                         PASSED       UNIT                         ACTIVATES
Sat 2024-10-26 00:00:00 CEST 15min left    Fri 2024-10-25 00:00:00 CEST 23h ago      dpkg-db-backup.timer         dpkg-db-backup.service
Sat 2024-10-26 00:00:00 CEST 15min left    Fri 2024-10-25 00:00:00 CEST 23h ago      logrotate.timer              logrotate.service
Sat 2024-10-26 06:39:59 CEST 6h left       Fri 2024-10-25 06:56:26 CEST 16h ago      apt-daily-upgrade.timer      apt-daily-upgrade.service
Sat 2024-10-26 10:27:42 CEST 10h left      Fri 2024-10-25 08:18:00 CEST 15h ago      man-db.timer                 man-db.service
Sat 2024-10-26 11:13:30 CEST 11h left      Fri 2024-10-25 21:06:00 CEST 2h 38min ago apt-daily.timer              apt-daily.service
Sat 2024-10-26 22:43:26 CEST 22h left      Fri 2024-10-25 22:43:26 CEST 1h 0min ago  systemd-tmpfiles-clean.timer systemd-tmpfiles-clean.service
Sun 2024-10-27 03:10:37 CET  1 day 4h left Sun 2024-10-20 03:11:00 CEST 5 days ago   e2scrub_all.timer            e2scrub_all.service
Mon 2024-10-28 01:12:51 CET  2 days left   Mon 2024-10-21 01:40:06 CEST 4 days ago   fstrim.timer                 fstrim.service

9 timers listed.

Relevant are apt-daily.timer which activates apt-daily.service. This unit-file will execute /usr/lib/apt/apt.systemd.daily update. The script takes care of reading the necessary APT parameters and performing an apt-get update to update the package lists.

The timer apt-daily-upgrade.timer triggers the service apt-daily-upgrade.service. The unit-file will perform an /usr/lib/apt/apt.systemd.daily install and this is where the actual "apt-get upgrade-magic" happens. If the appropriate APT-values are set outstanding updates will be downloaded and installed.

Notice the absence of a specific unattended-upgrades unit-file or timer as unattended-upgrades is really just a script to automate the APT package system.

This effectively means: You are able to configure when package-list updates will be done and updates are installed by modifying the OnCalendar= parameter via drop-in files for the apt-daily(-upgrade).timer files.
The Systemd.timer documentation and man 7 systemd.time (systemd.time documentation) have all the glorious details.

I wont go into further detail regarding the /usr/lib/apt/apt.systemd.daily script. If you want to know more I recommend executing the script with bash's -x parameter (also called debug mode). This way commands and values are printed out as the script is run.

root@host:~# bash -x /usr/lib/apt/apt.systemd.daily update
# Read the output, view the script, trace the parameters and then execute:
root@host:~# bash -x /usr/lib/apt/apt.systemd.daily lock_is_held update

Or if you are more interested in the actual "How are the updates installed?"-part, perform the following:

root@host:~# bash -x /usr/lib/apt/apt.systemd.daily install
# Read the output, view the script, trace the parameters and then execute:
root@host:~# bash -x /usr/lib/apt/apt.systemd.daily lock_is_held install

It's a good lesson in understanding APT-internals/what Debian is running "under the hood".

But again: I advise you to make sure that no actual updates are installed when you do so. In order to learn how to make sure read along. 😇

How does everything work together? What makes unattended-upgrades being unattended?

Let us recapitulate. We installed the unattended-upgrades package, checked the relevant Systemd unit & timer files and had a brief look at the /usr/lib/apt/apt.systemd.daily script which is responsible for triggering the appropriate APT and unattended-upgrades commands.

APT itself is configured via the file in /etc/apt/apt.conf.d/. How can APT (or any human) know the setting of a specific parameter? Sure, you can grep through all the files - but that would also most likely include files with syntax errors etc.

Luckily there is apt-config this allows us to query APT and read specific values. This also makes sure of validating everything. If you've configured an APT-parameter in a file but apt-config doesn't reflect this - it's simply not applied and you must start to search where the error is.

Armed with this knowledge we can execute the following two commands to check if our package-lists will be updated automatically via the apt-daily.service and if unattended-upgrades will install packages. If there is no associated value, apt-config won't print out anything.

The two settings which are set inside /etc/apt/apt.conf.d/20auto-upgrades are APT::Periodic::Update-Package-Lists and APT::Periodic::Unattended-Upgrade. The first activates the automatic package-list updates while the later enables the automatic installation of updates. If we check them on our system with the manually installed unattended-upgrades package we will get the following:

root@host:~# apt-config dump APT::Periodic::Update-Package-Lists
root@host:~# apt-config dump APT::Periodic::Unattended-Upgrade

This means no package-list updates, no installation of updates. And currently this is what we want to keep experimenting a little bit before we are ready to hit production.

A working unattended-upgrades will give the following values:

root@host:~# apt-config dump APT::Periodic::Update-Package-Lists
APT::Periodic::Update-Package-Lists "1";
root@host:~# apt-config dump APT::Periodic::Unattended-Upgrade
APT::Periodic::Unattended-Upgrade "1";

First dry-run

Time to start our first unattended-upgrades dry-run. This way we can watch what would be done without actually modifying anything. I recommend utilizing the -v parameter in addition to --dry-run as else the following first 8 lines from the unattended-upgrades output itself will be omitted. Despite them being the most valuable ones for most novice users.

root@host:~# unattended-upgrades --dry-run -v
Checking if system is running on battery is skipped. Please install powermgmt-base package to check power status and skip installing updates when the system is running on battery.
Starting unattended upgrades script
Allowed origins are: origin=Debian,codename=bookworm,label=Debian, origin=Debian,codename=bookworm,label=Debian-Security, origin=Debian,codename=bookworm-security,label=Debian-Security
Initial blacklist:
Initial whitelist (not strict):
Option --dry-run given, *not* performing real actions
Packages that will be upgraded: base-files bind9-dnsutils bind9-host bind9-libs dnsutils git git-man initramfs-tools initramfs-tools-core intel-microcode libc-bin libc-l10n libc6 libc6-i386 libcurl3-gnutls libexpat1 libnss-systemd libpam-systemd libpython3.11-minimal libpython3.11-stdlib libssl3 libsystemd-shared libsystemd0 libudev1 linux-image-amd64 locales openssl python3.11 python3.11-minimal qemu-guest-agent systemd systemd-sysv systemd-timesyncd udev
Writing dpkg log to /var/log/unattended-upgrades/unattended-upgrades-dpkg.log
/usr/bin/dpkg --status-fd 10 --no-triggers --unpack --auto-deconfigure --recursive /tmp/apt-dpkg-install-o5g9u2
/usr/bin/dpkg --status-fd 10 --no-triggers --configure libsystemd0:amd64 libsystemd-shared:amd64 systemd:amd64
/usr/bin/dpkg --status-fd 10 --no-triggers --unpack --auto-deconfigure /var/cache/apt/archives/systemd-sysv_252.30-1~deb12u2_amd64.deb /var/cache/apt/archives/udev_252.30-1~deb12u2_amd64.deb /var/cache/apt/archives/libudev1_252.30-1~deb12u2_amd64.deb
/usr/bin/dpkg --status-fd 10 --no-triggers --configure libudev1:amd64
/usr/bin/dpkg --status-fd 10 --configure --pending
Preconfiguring packages ...
Preconfiguring packages ...
/usr/bin/dpkg --status-fd 10 --no-triggers --unpack --auto-deconfigure /var/cache/apt/archives/libc6-i386_2.36-9+deb12u8_amd64.deb /var/cache/apt/archives/libc6_2.36-9+deb12u8_amd64.deb
/usr/bin/dpkg --status-fd 10 --no-triggers --configure libc6:amd64
/usr/bin/dpkg --status-fd 10 --no-triggers --unpack --auto-deconfigure /var/cache/apt/archives/libc-bin_2.36-9+deb12u8_amd64.deb
/usr/bin/dpkg --status-fd 10 --no-triggers --configure libc-bin:amd64
/usr/bin/dpkg --status-fd 10 --no-triggers --unpack --auto-deconfigure /var/cache/apt/archives/libc-l10n_2.36-9+deb12u8_all.deb /var/cache/apt/archives/locales_2.36-9+deb12u8_all.deb
/usr/bin/dpkg --status-fd 10 --configure --pending
/usr/bin/dpkg --status-fd 10 --no-triggers --unpack --auto-deconfigure /var/cache/apt/archives/intel-microcode_3.20240813.1~deb12u1_amd64.deb
/usr/bin/dpkg --status-fd 10 --configure --pending
/usr/bin/dpkg --status-fd 10 --no-triggers --unpack --auto-deconfigure /var/cache/apt/archives/python3.11_3.11.2-6+deb12u3_amd64.deb /var/cache/apt/archives/libpython3.11-stdlib_3.11.2-6+deb12u3_amd64.deb /var/cache/apt/archives/python3.11-minimal_3.11.2-6+deb12u3_amd64.deb /var/cache/apt/archives/libpython3.11-minimal_3.11.2-6+deb12u3_amd64.deb
/usr/bin/dpkg --status-fd 10 --configure --pending
/usr/bin/dpkg --status-fd 10 --no-triggers --unpack --auto-deconfigure /var/cache/apt/archives/git_1%3a2.39.5-0+deb12u1_amd64.deb /var/cache/apt/archives/git-man_1%3a2.39.5-0+deb12u1_all.deb
/usr/bin/dpkg --status-fd 10 --configure --pending
/usr/bin/dpkg --status-fd 10 --no-triggers --unpack --auto-deconfigure /var/cache/apt/archives/base-files_12.4+deb12u7_amd64.deb
/usr/bin/dpkg --status-fd 10 --no-triggers --configure base-files:amd64
/usr/bin/dpkg --status-fd 10 --configure --pending
/usr/bin/dpkg --status-fd 10 --no-triggers --unpack --auto-deconfigure /var/cache/apt/archives/initramfs-tools_0.142+deb12u1_all.deb /var/cache/apt/archives/initramfs-tools-core_0.142+deb12u1_all.deb
/usr/bin/dpkg --status-fd 10 --configure --pending
/usr/bin/dpkg --status-fd 10 --no-triggers --unpack --auto-deconfigure /var/cache/apt/archives/bind9-dnsutils_1%3a9.18.28-1~deb12u2_amd64.deb /var/cache/apt/archives/bind9-host_1%3a9.18.28-1~deb12u2_amd64.deb /var/cache/apt/archives/bind9-libs_1%3a9.18.28-1~deb12u2_amd64.deb /var/cache/apt/archives/dnsutils_1%3a9.18.28-1~deb12u2_all.deb
/usr/bin/dpkg --status-fd 10 --configure --pending
/usr/bin/dpkg --status-fd 10 --no-triggers --unpack --auto-deconfigure /var/cache/apt/archives/libexpat1_2.5.0-1+deb12u1_amd64.deb
/usr/bin/dpkg --status-fd 10 --configure --pending
/usr/bin/dpkg --status-fd 10 --no-triggers --unpack --auto-deconfigure /var/cache/apt/archives/qemu-guest-agent_1%3a7.2+dfsg-7+deb12u7_amd64.deb
/usr/bin/dpkg --status-fd 10 --configure --pending
/usr/bin/dpkg --status-fd 10 --no-triggers --unpack --auto-deconfigure /var/cache/apt/archives/libssl3_3.0.14-1~deb12u2_amd64.deb /var/cache/apt/archives/openssl_3.0.14-1~deb12u2_amd64.deb
/usr/bin/dpkg --status-fd 10 --configure --pending
/usr/bin/dpkg --status-fd 10 --no-triggers --unpack --auto-deconfigure /var/cache/apt/archives/libcurl3-gnutls_7.88.1-10+deb12u7_amd64.deb
/usr/bin/dpkg --status-fd 10 --configure --pending
/usr/bin/dpkg --status-fd 10 --no-triggers --unpack --auto-deconfigure /var/cache/apt/archives/linux-image-6.1.0-26-amd64_6.1.112-1_amd64.deb /var/cache/apt/archives/linux-image-amd64_6.1.112-1_amd64.deb
/usr/bin/dpkg --status-fd 10 --configure --pending
All upgrades installed
The list of kept packages can't be calculated in dry-run mode.
root@host:~#

We get told which configured origins will be used (see part 1), all packages on the black- and whitelist and which actual packages will be upgraded. Just like if you are executing apt-get upgrade manually.

Also there is the neat line Writing dpkg log to /var/log/unattended-upgrades/unattended-upgrades-dpkg.log informing us of a logfile being written. How nice!

The dpkg-commands are what normally happens in the background to install and configure the packages. In 99% of all cases this is irrelevant. Nevertheless they become invaluable when an update goes sideways or dpkg/apt can't properly configure a package.

Where do we find this information afterwards?

Logfiles

There are two logfiles being written:

1. /var/log/unattended-upgrades/unattended-upgrades-dpkg.log
2. /var/log/unattended-upgrades/unattended-upgrades.log

And how do they differ?

/var/log/unattended-upgrades/unattended-upgrades-dpkg.log has all output from dpkg/apt itself. You remember all these Preparing to unpack... packagename, Unpacking packagename, Setting up packagename lines? The lines you encounter when you execute apt-get manually? Who weren't present in the output from our dry-run? This gets logged into that file. So if you are wondering when a certain packages was installed or what went wrong, this is the logfile to look into.

/var/log/unattended-upgrades/unattended-upgrades.log contains the output from unattended-upgrades itself. This makes it possible to check what allowed origins/blacklists/whitelists, etc. were used in a run. Conveniently the output also includes the packages which are suitable for upgrading.

Options! Give me options!

Now that we know how we can execute a dry-run and retrace what happened it's time to have a look at the various options unattended-upgrades offers.

I recommend reading the config file /etc/apt/apt.conf.d/50unattended-upgrades once completely as the various options to fine-tune the behaviour are listed at the end. If you want unattended-upgrades to send mails, or only install updates on shutdown/reboot this is your way to go.

Or do you want an automatic reboot after unattended-upgrades has done its job (see: Unattended-Upgrade::Automatic-Reboot)? Ensuring the new kernel and system libraries are instantly used? This is your way to go.

Adding the Proxmox Repository to unattended-upgrades

Enabling updates for packages in different repositories means we have to add a new Repository to unattended-upgrades first. Using our knowledge from Part 1 and looking at the Release file for the Proxmox pve-no-subscription Debian Bookworm repository we can build the following origins-pattern:

"origin=Proxmox,codename=${distro_codename},label=Proxmox Debian Repository,a=stable";

A new dry-run will show us that the packages proxmox-default-kernel and proxmox-kernel-6.5 will be upgraded.

root@host:~# unattended-upgrades -v --dry-run
Checking if system is running on battery is skipped. Please install powermgmt-base package to check power status and skip installing updates when the system is runnin on battery.
Checking if connection is metered is skipped. Please install python3-gi package to detect metered connections and skip downloading updates.
Starting unattended upgrades script
Allowed origins are: origin=Debian,codename=bookworm,label=Debian, origin=Debian,codename=bookworm,label=Debian-Security, origin=Debian,codename=bookworm-security,labl=Debian-Security, origin=Proxmox,codename=bookworm,label=Proxmox Debian Repository,a=stable
Initial blacklist:
Initial whitelist (not strict):
Option --dry-run given, *not* performing real actions
Packages that will be upgraded: proxmox-default-kernel proxmox-kernel-6.5
Writing dpkg log to /var/log/unattended-upgrades/unattended-upgrades-dpkg.log
/usr/bin/dpkg --status-fd 10 --no-triggers --unpack --auto-deconfigure /var/cache/apt/archives/proxmox-kernel-6.8.8-2-pve-signed_6.8.8-2_amd64.deb /var/cache/apt/archves/proxmox-kernel-6.8_6.8.8-2_all.deb /var/cache/apt/archives/proxmox-default-kernel_1.1.0_all.deb
/usr/bin/dpkg --status-fd 10 --configure --pending
/usr/bin/dpkg --status-fd 10 --no-triggers --unpack --auto-deconfigure /var/cache/apt/archives/proxmox-kernel-6.5.13-5-pve-signed_6.5.13-5_amd64.deb /var/cache/apt/arhives/proxmox-kernel-6.5_6.5.13-5_all.deb
/usr/bin/dpkg --status-fd 10 --configure --pending
All upgrades installed
The list of kept packages can't be calculated in dry-run mode.

In the next step we will use this to see how blacklisting works.

Note: Enabling unattended-upgrades for the Proxmox packages on the Proxmox host itself is a controversial topic. In clustered & productive setups I wouldn't recommend it too. But given this is my single-node, homelab Proxmox I have no problem with it.

However I have no problem with enabling OS updates as this is no different from what Proxmox themselves do/recommend: https://pve.proxmox.com/pve-docs/pve-admin-guide.html#system_software_updates

Blacklisting packages

Excluding a certain package from the automatic updates can be done in two different ways. Either you don't include the repository into the Unattended-Upgrade::Origins-Pattern block - effectively excluding all packages in the repository. Or you exclude only single packages by listing them inside the Unattended-Upgrade::Package-Blacklist block. The configuration file has examples for the various patterns needed (exact match, name beginning with a certain string, escaping, etc.)

The following line will blacklist all packages starting with proxmox- in their name.

Unattended-Upgrade::Package-Blacklist {
    // The following matches all packages starting with linux-
    //  "linux-";

    // Blacklist all proxmox- packages
    "proxmox-";

    [...]
};

Executing a dry-run again will give the following result:

root@host:~# unattended-upgrades -v --dry-run
Checking if system is running on battery is skipped. Please install powermgmt-base package to check power status and skip installing updates when the system is running on battery.
Checking if connection is metered is skipped. Please install python3-gi package to detect metered connections and skip downloading updates.
Starting unattended upgrades script
Allowed origins are: origin=Debian,codename=bookworm,label=Debian, origin=Debian,codename=bookworm,label=Debian-Security, origin=Debian,codename=bookworm-security,label=Debian-Security, origin=Proxmox,codename=bookworm,label=Proxmox Debian Repository,a=stable
Initial blacklist: proxmox-
Initial whitelist (not strict):
No packages found that can be upgraded unattended and no pending auto-removals
The list of kept packages can't be calculated in dry-run mode.

"The following packages have been kept back" - What does this mean? Will unattended-upgrades help me?

Given is the following output from a manual apt-get upgrade run.

root@host:~# apt-get upgrade
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
Calculating upgrade... Done
The following packages have been kept back:
  proxmox-default-kernel proxmox-kernel-6.5
0 upgraded, 0 newly installed, 0 to remove and 2 not upgraded.

The message means that the packages are part of so-called PhasedUpdates. Sadly documentation regarding this in Debian is a bit sparse. The manpage for apt_preference(5) has a paragraph about it but that's pretty much it.

Ubuntu has a separate Wiki article about it, as their update manager honors the setting: https://wiki.ubuntu.com/PhasedUpdates

What it means is that some updates won't be rolled out to all servers immediately. Instead a random number is generated which determines if the update is applied or not.

Quote from apt_preferences(5):
"A system's eligibility to a phased update is determined by seeding random number generator with the package source name, the version number, and /etc/machine-id, and then calculating an integer in the range [0, 100]. If this integer is larger than the Phased-Update-Percentage, the version is pinned to 1, and thus held back. Otherwise, normal policy rules apply."

Unattended-upgrades however will ignore this and install the updates. If that is good or bad depends on your situation. Luckily there was some recent activity in the GitHub Issue regarding this topic, so it may be resolved soon-ish: unattended-upgrades on GitHub, issue 259: Please honor Phased-Update-Percentage for package versions

Enabling unattended-upgrades

Now it's finally time to enable unattended-upgrades for our system. Execute dpkg-reconfigure -f noninteractive unattended-upgrades and check that the /etc/apt/apt.conf.d/20auto-upgrades file is present with the following content:

root@host:~# cat /etc/apt/apt.conf.d/20auto-upgrades
APT::Periodic::Update-Package-Lists "1";
APT::Periodic::Unattended-Upgrade "1";

After that verify that APT has indeed the correct values for those parameters:

root@host:~# apt-config dump APT::Periodic::Update-Package-Lists
APT::Periodic::Update-Package-Lists "1";
root@host:~# apt-config dump APT::Periodic::Unattended-Upgrade
APT::Periodic::Unattended-Upgrade "1";

You are then able to determine when the first run will happen by checking via systemctl list-timers apt-daily.timer apt-daily-upgrade.timer.

root@host:~# systemctl list-timers apt-daily.timer apt-daily-upgrade.timer
NEXT                        LEFT          LAST                        PASSED  UNIT                    ACTIVATES
Sat 2024-10-26 03:39:58 UTC 16min left    Fri 2024-10-25 09:12:58 UTC 18h ago apt-daily.timer         apt-daily.service
Sat 2024-10-26 06:21:30 UTC 2h 58min left Fri 2024-10-25 06:24:40 UTC 20h ago apt-daily-upgrade.timer apt-daily-upgrade.service

Set yourself a reminder in your calendar to check the logfiles and enjoy your automatic updates!

How to check the health of a Debian mirror

Remember how I, in part 1 of this series, mentioned that Debian mirrors are rarely out-of-sync, etc.? Yep, and now it happened while I was typing this post. The perfect opportunity to show you how to check your Debian mirror.

The error I got was the following:

root@host:~# apt-get update
Hit:1 http://security.debian.org/debian-security bookworm-security InRelease
Hit:2 http://debian.tu-bs.de/debian bookworm InRelease
Get:3 http://debian.tu-bs.de/debian bookworm-updates InRelease [55.4 kB]
Reading package lists... Done
E: Release file for http://debian.tu-bs.de/debian/dists/bookworm-updates/InRelease is expired (invalid since 16d 0h 59min 33s). Updates for this repository will not be applied.

The reason is that the InRelease file contains a Valid-Until timestamp. And currently it has the following value:
Valid-Until: Sat, 22 Jun 2024 20:12:12 UTC

As this error originates on a remote host there is nothing I can do apart from switching to another Debian repository.

But how can you actually check that? https://mirror-master.debian.org/status/mirror-status.html lists the status of all Debian Mirrors. If we search for debian.tu-bs.de we can see that the mirror indeed has problems and since when the error exists.

Side note: Checking the mirror hierarchy can also be relevant sometimes: https://mirror-master.debian.org/status/mirror-hierarchy.html

Also.. 22 days without noticing that the Debian mirror I use is broken? Yeah.. Let's define a monitoring check for that. Something I didn't do for my setup at home.

As this would make this article unnecessarily larger I made a separate blog post about it. So feel free to read this next: How to monitor your APT-repositories with Icinga