Status changed to 'Confirmed' because the bug affects multiple users.
** Changed in: systemd (Ubuntu Bionic)
Status: New => Confirmed
--
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 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
