> that was the atime yep, really no way around updating the atime, as systemd of course needs to access the file to check if the content is the same or not
-- 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: New Status in systemd source package in Focal: Fix Committed Status in systemd source package in Groovy: Fix Committed 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
