[systemd-devel] Simple oneshot service before switching root leads to no /var mount

[Lennart Poettering]

On Mon, 28.09.15 15:40, Aaron_Wright at selinc.com (Aaron_Wright at selinc.com) wrote:

> I'm rolling my own initrd, and I'm trying to run a oneshot service in 
> initrd just before the switch root happens. I added this unit to the 
> initrd and enabled it.
> 
> [Unit]
> Description=Test Unit
> Requires=initrd-fs.target
> After=initrd-fs.target
> 
> [Service]
> Type=oneshot
> ExecStart=/bin/sh -c "echo hello"
> 
> [Install]
> RequiredBy=initrd-switch-root.target
> 
> The service does run, and I get "hello" in the journal, but then my /var 
> mount doesn't mount. I'm having a hard time correlating the two seeming 
> different things. The var.mount unit complains about a failed dependency. 
> It's dependency is dev-disk-by\x2dpartlabel-varfs.device, which has no 
> logs, is loaded, but inactive (dead). There is also a fsck dependency that 
> is loaded, but inactive (dead).

Well, the var.mount backing device never appeared then.

> Without this simple oneshot service in initrd, everything works fine, fsck 
> checks varfs and /var is mounted. Thoughts?

Well, that service does not set DefaultDependencies=no, hence will be
ordered after local-fs.target, and hence after var.mount... but you
also use it in earliest boot and effectively order it before
initrd-switch-root.target. Which means you have a cyclic dep, as you
have a service that wants to be in late boot, but is ordered into
early boot...

systemd should log about cyclic deps like this.

Anyway, long story short: you must set DefaultDependency=no for all
initrd and early-bird services, as otherwise your service will be
placed into late boot, via the implicit default deps, and that makes
no sense for the initrd.

Lennart

-- 
Lennart Poettering, Red Hat