[systemd-devel] systemd-fsck-root semantics

[Daniel Drake]

On Wed, Jul 2, 2014 at 1:13 PM, Zbigniew Jędrzejewski-Szmek
<zbyszek at in.waw.pl> wrote:
> Thinking about it, I'm not sure how the new systemd would know that
> systemd-fsck at dev-something.service from the initramfs is the same
> thing as systemd-fsck-root.service. Maybe that's the problem?
>
> Currently systemd-fsck-root.service does nothing if / is mounted rw,
> which of course is used by almost everybody, so I think you might
> be using codepaths that are rarely tested.

If I'm reading things right, actually the default behaviour is (when
no hints are supplied in kernel cmdline) :
 1. systemd runs fsck on root from initramfs
 2. systemd mounts root fs ro
 3. switch-root onto real system
 4. systemd-fsck-root runs
 5. systemd-remount-fs remounts / as rw

Also just noticed another interesting thing -
systemd-fsck-root.service is only loaded dynamically, when /etc/fstab
has a non-zero passno for /. So maybe the idea is that anyone running
a regular and modern dracut/systemd setup sets passno=0 for / in
fstab, with the knowledge that fsck of / is done by the initramfs.

Daniel