CentOS 7.4 released: Potential Sendmail issues
CentOS 7.4 has been released an updates for it have it the YUM repositories. On BlueOnyx 5209R this *may* cause a Sendmail outage.
After the CentOS 7.4 updates hit the CentOS YUM repositories, we noticed that several (but not all) of our own BlueOnyx 5209R instances experienced Sendmail issues. Sendmail was dead and refused to restart. The "systemctl restart sendmail" command was hanging a long time before it failed.
However, on other 5209R's the update either went through without issue and Sendmail could be restarted just fine.
We quickly discovered that the affected boxes had lost the symlink from /var/run -> /run and that this was responsible for the Sendmail restart problem.
If you're affected by this problem, then please do this:
One work around that works is this:
Edit /lib/systemd/system/sendmail.service and find this line:
Change it to this:
Then run this two commands:
systemctl restart sendmail
The first notifies Systemd about the changed Sendmail unit-file and the second one then successfully restart Sendmail.
We're still looking at the broader issue of the /var/run symlink and why that went away and what other issues (if any) it may have for us.