[ThinLinc-technical] systemd unit file bugs

[Jonathan Buzzard]

First off the vsmagent.service file is being installed with execute 
permissions, so I see things like this in my log files

systemd: Configuration file /usr/lib/systemd/system/vsmagent.service is 
marked executable. Please remove executable permission bits. Proceeding 
anyway.

You can use "systemctl daemon-reload" to trigger it.

Second the way the unit file is written the service agent will fail to 
start in many circumstances. So you have the following

[Unit]
Description=ThinLinc VSM agent
After=network.target

Basically using "After=network.target" is about as much use as a 
chocolate teapot. What I am seeing on a system where the network 
interface is a 802.ad bond is the following

2021-06-01 20:44:29 WARNING vsmagent: Couldn't lookup host 
vsmserver.mycorp.com: [Errno -2] Name or service not known

That's because network.target only indicates that the network management 
stack is up, it doesn't mean there is a useable network connection. It 
takes a handful of seconds after the 802.3ad LAG is started for it to 
actually be able to handle traffic. In that time the vsmagent starts 
can't lookup the vsmserver hostname and unhelpfully fails.

You may well see the same if the server is doing DHCP to obtain it's IP 
address.

What you want is to use the following in your unit file

After=network-online.target
Wants=network-online.target

Though to avoid slowing down the boot, you should probably be watching 
rtnetlink and retrying when network reconfigurations happen. The above 
modification is basically having systemd working around broken behaviour 
in the vsmagent demon.

Note depending on your circumstances you might want to do something like 
the following to make the vsmagent wait till any remote file systems are 
mounted. For example if users home directories are on an NFS share.

mkdir -p /etc/systemd/system/vsmagent.service.d
echo -e "[Unit]\nAfter=network-online.target remote-fs.target" > 
/etc/systemd/system/vsmagent.service.d/waitforremotefs.conf
systemctl daemon-reload


JAB.

-- 
Jonathan A. Buzzard                         Tel: +44141-5483420
HPC System Administrator, ARCHIE-WeSt.
University of Strathclyde, John Anderson Building, Glasgow. G4 0NG