System Input Plugin should have also variable for determinate path to /hostfs/var

[lukasmrtvy]

Bug report

System Input Plugin should have also variable for determinate path to /hostfs/var

Logs:
2017-10-13T04:52:40Z E! Error in plugin [inputs.system]: open /var/run/utmp: no such file or directory

HOST_VAR=/hostfs/var should be a solution, just like in HOST_ETC= case

Relevant telegraf.conf:

[inputs.system]

System info:

Telegraph 1.4.2
Alpine 3.6

Steps to reproduce:

docker run -d --name telegraf --net host -v /:/hostfs:ro -e HOST_MOUNT_PREFIX=/hostfs -e HOST_ETC=/hostfs/etc mytelegraf

Proposal:

docker run -d --name telegraf -v /:/hostfs:ro -e HOST_MOUNT_PREFIX=/hostfs -e HOST_ETC=/hostfs/etc -e HOST_VAR=/hostfs/var mytelegraf

or

docker run -d --name telegraf -v /:/hostfs:ro -e HOST_MOUNT_PREFIX=/hostfs -e HOSTFS_PREFIX=/hostfs mytelegraf

Additional info:

There are no steps in docs to run telegraph in docker with host monitoring.

For example:
--net host ?
--cap_add ?
--priviledged ?

Thanks

[danielnelson]

@shirou Do you think we should add a HOST_VAR environment variable support to gopsutil? I believe the relevant code is https://github.com/shirou/gopsutil/blob/master/host/host_linux.go#L135

[danielnelson]

@muhahacz I know some people have used the advice in this comment for setup: #1544 (comment). I agree we need to do additional testing and add some setup advice to the documentation.

[shirou]

@danielnelson I agree to add environmental variable support to host.Users. Something like HOST_VAR as described proposal?

[danielnelson]

@shirou Yes, I think so. I'll submit a PR later today.

[lukasmrtvy]

Seems its fixed in gopsutil v2.17.10.
Will it be available in 1.4.4 ?
Thanks

[lukasmrtvy]

@shirou @danielnelson

In this case HOST_VAR=/hostfs/var/ variable does not work as expected..

2017-11-16T15:16:10Z E! Error in plugin [inputs.system]: open /hostfs/var/run/utmp: no such file or directory

Container:
ls -lha /hostfs/var/
lrwxrwxrwx 1 root root 4 Nov 8 21:15 run -> /run

Host:
ls -lha /var/
lrwxrwxrwx 1 root root 4 Nov 8 21:15 run -> /run

Symlink breaks /hostfs/ prefix

utmp in container is located here:
/hostfs/run/utmp

Workaround for now is bind it directly like:
-v /var/run/utmp:/var/run/utmp:ro

[danielnelson]

Thanks for the update @muhahacz, this seems similar to the issues we had with /etc/mtab #1544 (comment)

I'm not sure if there is a better way to address this than your workaround.