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-- You received this bug notification because you are a member of Ubuntu Touch seeded packages, which is subscribed to systemd in Ubuntu. https://bugs.launchpad.net/bugs/1891215 Title: systemd-resolved re-creates /run/systemd/resolve/*resolv.conf for every IPv6 RA received Status in systemd: Unknown Status in systemd package in Ubuntu: Fix Released Status in systemd source package in Bionic: Confirmed Status in systemd source package in Focal: Fix Committed Status in systemd source package in Groovy: Fix Released Status in systemd source package in Hirsute: Fix Committed Bug description: [impact] networking changes, like RA events, can cause systemd-resolved to re- write the resolv.conf file, even if the contents didn't change, resulting in unnecessary increased amount of inotify events [test case] see original description for ipv6ra-related reproducer, or simple reproducer here: configure networkd with some config for (e.g.) eth0, but not a config that would result in /etc/resolv.conf changing when the interface goes up/down - for example, use static config with no DNS search domains. Then bring eth0 up/down while observing the md5sum (file content) does not change but the mtime does change. root@lp1891215-h:~# ip l set down dev eth0 root@lp1891215-h:~# md5sum /etc/resolv.conf db23e80078515192c312e5f321ff0340 /etc/resolv.conf root@lp1891215-h:~# stat -t -L /etc/resolv.conf /etc/resolv.conf 740 8 81a4 101 103 fc 188 1 0 0 1625238218 1625238216 1625238216 0 4096 root@lp1891215-h:~# ip l set up dev eth0 root@lp1891215-h:~# md5sum /etc/resolv.conf db23e80078515192c312e5f321ff0340 /etc/resolv.conf root@lp1891215-h:~# stat -t -L /etc/resolv.conf /etc/resolv.conf 740 8 81a4 101 103 fc 188 1 0 0 1625238227 1625238226 1625238226 0 4096 [regression potential] regressions would result in incorrect or missing data in the resolv.conf file, possibly resulting in dns failures or errors [scope] this is needed for h and eralier this is (potentially) fixed upstream by f3e1f00d03445911ee73729219cea88c8a70c612 which in first included in v248, so this is needed in hirsute and earlier [original description] # Issue description: On 2 Linode VMs that are used as lxd hosts, we noticed that /run/systemd/resolve/*resolv.conf were re-created quite frequently (~ once per second). We noticed because of the log noise from lxd's dnsmasq instance using inotify to watch the target of /etc/resolv.conf (which points to the stub-resolv.conf in our case). This was (wrongly) reported as a lxd bug (https://github.com/lxc/lxd/issues/7765) until it became apparent it was more likely to be a problem with systemd(-resolved)?. The log noise is the observable problem that would be nice to see addressed: root@lxd02:~# uptime 17:55:48 up 9:52, 1 user, load average: 0.18, 0.11, 0.05 root@lxd02:~# journalctl -b0 | grep -cF dnsmasq 158609 Upon further investigation, it seems that systemd-resolved re-creates the resolv.conf and stub-resolv.conf files whenever an IPv6 RA is received. 1) One can observe that by setting systemd-resolved's service in debug mode: $ sudo systemctl edit systemd-resolved and in the editor that is opened, add and save this content: [Service] Environment=SYSTEMD_LOG_LEVEL=debug then restart systemd-resolved and watch the logs scroll by with: $ journalctl -fu systemd-resolved 3) In another terminal, watch the files be recreated with: watch -d -n 0.1 stat /run/systemd/resolve/stub-resolv.conf 3) In yet another terminal, run a packet capture and watch "ICMP6, router advertisement" messages come by: sudo tcpdump -ni eth0 icmp6 You will see that every time a RA packet comes in, resolved's journal will log this: Aug 11 17:33:55 lxd02 systemd-resolved[15368]: Sent message type=signal sender=n/a destination=n/a path=/org/freedesktop/resolve1 interface=org.freedesktop.DBus.Properties member=PropertiesChanged cookie=244 reply_cookie=0 signature=sa{sv}as error-name=n/a error- message=n/a And the stat monitoring terminal will blink to highlight the new inode and timestamps of the freshly replaced stub-resolv.conf file. # Additional information: root@lxd02:~# lsb_release -rd Description: Ubuntu 20.04.1 LTS Release: 20.04 root@lxd02:~# apt-cache policy systemd systemd: Installed: 245.4-4ubuntu3.2 Candidate: 245.4-4ubuntu3.2 Version table: *** 245.4-4ubuntu3.2 500 500 http://archive.ubuntu.com/ubuntu focal-updates/main amd64 Packages 100 /var/lib/dpkg/status 245.4-4ubuntu3 500 500 http://archive.ubuntu.com/ubuntu focal/main amd64 Packages root@lxd02:~# uname -a Linux lxd01 5.4.0-42-generic #46-Ubuntu SMP Fri Jul 10 00:24:02 UTC 2020 x86_64 x86_64 x86_64 GNU/Linux To manage notifications about this bug go to: https://bugs.launchpad.net/systemd/+bug/1891215/+subscriptions -- Mailing list: https://launchpad.net/~touch-packages Post to : touch-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~touch-packages More help : https://help.launchpad.net/ListHelp
