Over the last few months, I upgraded my Debian machines from bullseye to bookworm. The process was uneventful (besides the asterisk issue described below), but I ended up reconfiguring several things afterwards in order to modernize my upgraded machines.

Logcheck

I noticed in this release that the transition to journald is essentially complete. This means that rsyslog is no longer needed on most of my systems:

apt purge rsyslog

Once that was done, I was able to comment out the following lines in /etc/logcheck/logcheck.logfiles.d/syslog.logfiles:

#/var/log/syslog
#/var/log/auth.log

I did have to adjust some of my custom logcheck rules, particularly the ones that deal with kernel messages:

--- a/logcheck/ignore.d.server/local-kernel
+++ b/logcheck/ignore.d.server/local-kernel
@@ -1,1 +1,1 @@
-^\w{3} [ :[:digit:]]{11} [._[:alnum:]-]+ kernel: \[[0-9. ]+]\ IN=eno1 OUT= MAC=[0-9a-f:]+ SRC=[0-9a-f.:]+
+^\w{3} [ :[:digit:]]{11} [._[:alnum:]-]+ kernel: (\[[0-9. ]+]\ )?IN=eno1 OUT= MAC=[0-9a-f:]+ SRC=[0-9a-f.:]+

Then I moved local entries from /etc/logcheck/logcheck.logfiles to /etc/logcheck/logcheck.logfiles.d/local.logfiles (/var/log/syslog and /var/log/auth.log are enabled by default when needed) and removed some files that are no longer used:

rm /var/log/mail.err*
rm /var/log/mail.warn*
rm /var/log/mail.info*

Finally, I had to fix any unescaped | characters in my local rules. For example error == NULL || \*error == NULL must now be written as error == NULL \|\| \*error == NULL.

Networking

After the upgrade, I got a notice that the isc-dhcp-client is now deprecated and so I removed if from my system:

apt purge isc-dhcp-client

This however meant that I need to ensure that my network configuration software does not depend on the now-deprecated DHCP client.

On my laptop, I was already using NetworkManager for my main network interfaces and that has built-in DHCP support.

Migration to systemd-networkd

On my backup server, I took this opportunity to switch from ifupdown to systemd-networkd by removing ifupdown:

apt purge ifupdown
rm /etc/network/interfaces

putting the following in /etc/systemd/network/20-wired.network:

[Match]
Name=eno1

[Network]
DHCP=yes
MulticastDNS=yes

and then enabling/starting systemd-networkd:

systemctl enable systemd-networkd
systemctl start systemd-networkd

I also needed to install polkit:

apt install --no-install-recommends policykit-1

in order to allow systemd-networkd to set the hostname.

In order to start my firewall automatically as interfaces are brought up, I wrote a dispatcher script to apply my existing iptables rules.

Migration to predictacle network interface names

On my Linode server, I did the same as on the backup server, but I put the following in /etc/systemd/network/20-wired.network since it has a static IPv6 allocation:

[Match]
Name=enp0s4

[Network]
DHCP=yes
Address=2600:3c01::xxxx:xxxx:xxxx:939f/64
Gateway=fe80::1

and switched to predictable network interface names by deleting these two files:

• /etc/systemd/network/50-virtio-kernel-names.link
• /etc/systemd/network/99-default.link

and then changing eth0 to enp0s4 in:

• /etc/network/iptables.up.rules
• /etc/network/ip6tables.up.rules
• /etc/rc.local (for OpenVPN)
• /etc/logcheck/ignored.d.*/*

Then I regenerated all initramfs:

update-initramfs -u -k all

and rebooted the virtual machine.

Giving systemd-resolved control of /etc/resolv.conf

After reading this history of DNS resolution on Linux, I decided to modernize my resolv.conf setup and let systemd-resolved handle /etc/resolv.conf.

I installed the package:

apt install systemd-resolved

and then removed no-longer-needed packages:

apt purge openresolv resolvconf avahi-daemon

I also disabled support for Link-Local Multicast Name Resolution (LLMNR) after reading this person's reasoning by putting the following in /etc/systemd/resolved.conf.d/llmnr.conf:

[Resolve]
LLMNR=no

I verified that mDNS is enabled and LLMNR is disabled:

$ resolvectl mdns
Global: yes
Link 2 (enp0s25): yes
Link 3 (wlp3s0): yes
$ resolvectl llmnr
Global: no
Link 2 (enp0s25): no
Link 3 (wlp3s0): no

Note that if you want auto-discovery of local printers using CUPS, you need to keep avahi-daemon and ensure that systemd-resolved does not conflict with it.

DNS resolution problems with ifupdown

Also, if you haven't migrated to systemd-networkd yet and are still using ifupdown with a static IP address, you will likely run into DNS problems which can be fixed using the following patch to /etc/network/if-up.d/resolved:

@@ -43,11 +43,11 @@ if systemctl is-enabled systemd-resolved > /dev/null 2>&1; then
     fi
     if  [ -n "$NEW_DNS" ]; then
         cat <<EOF >"$mystatedir/ifupdown-${ADDRFAM}-$interface"
-"$DNS"="$NEW_DNS"
+$DNS="$NEW_DNS"
 EOF
         if  [ -n "$NEW_DOMAINS" ]; then
             cat <<EOF >>"$mystatedir/ifupdown-${ADDRFAM}-$interface"
-"$DOMAINS"="$NEW_DOMAINS"
+$DOMAINS="$NEW_DOMAINS"
 EOF
         fi
     fi
@@ -66,7 +66,7 @@ EOF
     # ignore errors due to nonexistent file
     md5sum "$mystatedir/isc-dhcp-v4-$interface" "$mystatedir/isc-dhcp-v6-$interface" "$mystatedir/ifupdown-inet-$interface" "$mystatedir/ifupdown-inet6-$interface" > "$newstate" 2> /dev/null || true
     if ! cmp --silent "$oldstate" "$newstate" 2>/dev/null; then
-        DNS DNS6 DOMAINS DOMAINS6 DEFAULT_ROUTE
+        unset DNS DNS6 DOMAINS DOMAINS6 DEFAULT_ROUTE
         # v4 first
         if [ -e "$mystatedir/isc-dhcp-v4-$interface" ]; then
             . "$mystatedir/isc-dhcp-v4-$interface"

and make sure you have nameservers setup in your static config, for example one of my servers' /etc/network/interfaces looks like this:

iface enp4s0 inet static
     address 192.168.1.2
     netmask 255.255.255.0
     gateway 192.168.1.1
     dns-nameservers 149.112.121.20
     dns-nameservers 149.112.122.20
     pre-up iptables-restore /etc/network/iptables.up.rules

Dynamic DNS

I replaced ddclient with inadyn since it doesn't work with no-ip.com anymore, using the configuration I described in an old blog post.

chkrootkit

I moved my customizations in /etc/chkrootkit.conf to /etc/chkrootkit/chkrootkit.conf after seeing this message in my logs:

WARNING: /etc/chkrootkit.conf is deprecated. Please put your settings in /etc/chkrootkit/chkrootkit.conf instead: /etc/chkrootkit.conf will be ignored in a future release and should be deleted.

ssh

As mentioned in Debian bug#1018106, to silence the following warnings:

sshd[6283]: pam_env(sshd:session): deprecated reading of user environment enabled

I changed the following in /etc/pam.d/sshd:

--- a/pam.d/sshd
+++ b/pam.d/sshd
@@ -44,7 +44,7 @@ session    required     pam_limits.so
 session    required     pam_env.so # [1]
 # In Debian 4.0 (etch), locale-related environment variables were moved to
 # /etc/default/locale, so read that as well.
-session    required     pam_env.so user_readenv=1 envfile=/etc/default/locale
+session    required     pam_env.so envfile=/etc/default/locale

 # SELinux needs to intervene at login time to ensure that the process starts
 # in the proper default security context.  Only sessions which are intended

I also made the following changes to /etc/ssh/sshd_config.d/local.conf based on the advice of ssh-audit 2.9.0:

-KexAlgorithms curve25519-sha256@libssh.org,curve25519-sha256,diffie-hellman-group14-sha256,diffie-hellman-group16-sha512,diffie-hellman-group18-sha512,diffie-hellman-group-exchange-sha256
+KexAlgorithms curve25519-sha256@libssh.org,curve25519-sha256,sntrup761x25519-sha512@openssh.com,diffie-hellman-group16-sha512,diffie-hellman-group18-sha512

Unwanted power management

I ran into a problem with one of my servers where it would suspend itself after a certain amount of time. This was due to default GDM behaviour it turns out and while I could tell gdm not to sleep on inactivity, I instead put the following in /etc/systemd/sleep.conf.d/nosuspend.conf to fully disable systemd-based suspend or hibernate:

[Sleep]
AllowSuspend=no
AllowHibernation=no
AllowSuspendThenHibernate=no
AllowHybridSleep=no

Asterisk has been removed from Debian

The only major problem I ran into while upgrading to bookworm is that I discovered that Asterisk has been removed from stable and testing. For some reason, this was not mentioned in the release notes and I have not yet found a good solution.

If you upgrade to bookworm, be warned that the bullseye packages will remain installed (and will work fine in my experience) unless you "clean them up" with apt purge '~o' accidentally and then you'll have to fetch these old debs manually.