Red Hat Bugzilla – Bug 1478214
Unit files wait for network.target instead of network-online.target
Last modified: 2017-12-12 05:18:37 EST
Description of problem:
The zabbix-agent.service file specifies network.target in its After=
line because the Zabbix agent requires working network at startup.
Unfortunately, network.target is essentially meaningless at startup;
you need network-online.target for that purpose (see
The result of this is a race condition where sometimes at startup,
if the network is not yet working when the agent starts, it fails to
resolve the hostname of the server that it needs to communicate with.
Sometimes this fails to correct itself once the network really is
working, and a restart of the zabbix-agent service is required for
monitoring to resume (and while the fact that it never corrects itself
sometimes ought to be fixed upstream, we shouldn't end up in this
situation to begin with because we should be ordering this service
after the correct target).
This is likely a problem with all the other service files as well, as
they all order themselves after network.target instead of
Version-Release number of selected component (if applicable):
The incorrect After= line in /usr/lib/systemd/system/zabbix-agent.service
is trivial to see. Witnessing a loss of the race at startup reliably is
probably somewhat difficult, but also probably unnecessary.
Steps to Reproduce:
1. Setup zabbix-agent to talk to a remote server
2. Configure few enough other services as enabled at startup that
zabbix-agent is likely to start prior to the network interfaces being
zabbix-agent sometimes starts before the network is available, logs
failure to resolve the hostname of its server, and then does not send
any active check data to the server, either for some interval of time,
or indefinitely until it is restarted.
zabbix-agent only starts once the network is available.
Zabbix doesn't necessarily need to resolve a name, as you can specify an IP address as well. In particular, in the case of an active-only-agent I can imagine it being able to start, since it's not binding to any interface that might be missing. The startup historically involved an invocation of res_init() to initialize name resolution. This used to happen only once, so if resolv.conf was empty or wrong, this never fixed itself. This has changed for most maintained releases: https://support.zabbix.com/browse/ZBXNEXT-1862
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