Public bug reported:
[impact]
on a system where systemd-resolved is running, if dhclient is used on
more than 5 interfaces, it calls the '/etc/dhcp/dhclient-enter-
hooks.d/resolved' script multiple times, which then restarts systemd-
resolved multiple times, triggering the unit's start-limit throttle
which results in the unit entering failed state
[test case]
on a system with more than 5 available interfaces to run dhclient on
(where all the interfaces will get a dhcp response), run dhclient with
the interfaces:
$ dhclient ens8 ens9 ens10 ens11 ens12 ens13 ens14 ens15
check if systemd-resolved failed:
$ journalctl -b -1 -u systemd-resolved
...
Aug 09 00:38:08 sf316232-b systemd[1]: systemd-resolved.service: Start request
repeated too quickly.
Aug 09 00:38:08 sf316232-b systemd[1]: systemd-resolved.service: Failed with
result 'start-limit-hit'.
Aug 09 00:38:08 sf316232-b systemd[1]: Failed to start Network Name Resolution.
[regression potential]
failure to start/stop/restart systemd-resolved, or problems adding
dhclient-provided DNS nameservers to systemd-resolved
[scope]
this is needed only for b/f
the dhclient 'hook' script is provided by the systemd package in focal
and earlier, and needs fixing in those releases
in h and later, the 'hook' script is included in the isc-dhcp-client
package and notifies systemd-resolved in a more direct way without
requiring restarting, and so doesn't trigger the restart limiting.
** Affects: systemd (Ubuntu)
Importance: Undecided
Status: Invalid
** Affects: systemd (Ubuntu Bionic)
Importance: Medium
Assignee: Dan Streetman (ddstreet)
Status: In Progress
** Affects: systemd (Ubuntu Focal)
Importance: Medium
Assignee: Dan Streetman (ddstreet)
Status: In Progress
** Also affects: systemd (Ubuntu Bionic)
Importance: Undecided
Status: New
** Also affects: systemd (Ubuntu Focal)
Importance: Undecided
Status: New
** Changed in: systemd (Ubuntu)
Status: New => Invalid
** Changed in: systemd (Ubuntu Bionic)
Status: New => In Progress
** Changed in: systemd (Ubuntu Focal)
Status: New => In Progress
** Changed in: systemd (Ubuntu Bionic)
Importance: Undecided => Medium
** Changed in: systemd (Ubuntu Focal)
Importance: Undecided => Medium
** Changed in: systemd (Ubuntu Bionic)
Assignee: (unassigned) => Dan Streetman (ddstreet)
** Changed in: systemd (Ubuntu Focal)
Assignee: (unassigned) => Dan Streetman (ddstreet)
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https://bugs.launchpad.net/bugs/1939255
Title:
dhclient triggers systemd-resolved start limit when processing more
than 5 interfaces at once
Status in systemd package in Ubuntu:
Invalid
Status in systemd source package in Bionic:
In Progress
Status in systemd source package in Focal:
In Progress
Bug description:
[impact]
on a system where systemd-resolved is running, if dhclient is used on
more than 5 interfaces, it calls the '/etc/dhcp/dhclient-enter-
hooks.d/resolved' script multiple times, which then restarts systemd-
resolved multiple times, triggering the unit's start-limit throttle
which results in the unit entering failed state
[test case]
on a system with more than 5 available interfaces to run dhclient on
(where all the interfaces will get a dhcp response), run dhclient with
the interfaces:
$ dhclient ens8 ens9 ens10 ens11 ens12 ens13 ens14 ens15
check if systemd-resolved failed:
$ journalctl -b -1 -u systemd-resolved
...
Aug 09 00:38:08 sf316232-b systemd[1]: systemd-resolved.service: Start
request repeated too quickly.
Aug 09 00:38:08 sf316232-b systemd[1]: systemd-resolved.service: Failed with
result 'start-limit-hit'.
Aug 09 00:38:08 sf316232-b systemd[1]: Failed to start Network Name
Resolution.
[regression potential]
failure to start/stop/restart systemd-resolved, or problems adding
dhclient-provided DNS nameservers to systemd-resolved
[scope]
this is needed only for b/f
the dhclient 'hook' script is provided by the systemd package in focal
and earlier, and needs fixing in those releases
in h and later, the 'hook' script is included in the isc-dhcp-client
package and notifies systemd-resolved in a more direct way without
requiring restarting, and so doesn't trigger the restart limiting.
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https://bugs.launchpad.net/ubuntu/+source/systemd/+bug/1939255/+subscriptions
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