Le 21/11/2014 00:41, Lennart Poettering a écrit :
On Thu, 20.11.14 17:23, Didier Roche (didro...@ubuntu.com) wrote:
a) make /etc writable before systemd is invoked. If you use an initrd
this is without risk, given that the initrd should really invoke
fsck on the root disk anyway, and there's hence little reason to
transition to a read-only root, rather than just doing rw
right-away.
Interesting, I run that through our kernel team. However, we run fsck a
little bit later on in the boot process to be able to pipe the output to
plymouth.
At least on Fedora plymouth already runs on the initrd. If Ubuntu does
the same, then there shouldn't be a difference regarding where fsck is
run...
Note that running fsck in the initrd for the root fs is really the
right thing to do: running fsck from the file system you are about to
check, which you hence cannot trust, is really wrong.
I'm not sure we should then have two code paths:
- one fscking from the initrd if /etc/machine-id is empty (like after a
factory reset), showing the results and eventual failures to the user in
some way
- and then, the general use case: fscking through the systemd service via
systemd-fsck-root.service before local-fs.target and piping the result in
plymouth
The latter is useful only really on non-initrd boots where there isn't
any initrd where the fsck could run. General purpose distributions
should really run fsck in the initrd.
Note that systemd-fsck-root.service skips itself when it notices that
the fs was already checked (via a flag file in /run).
Indeed, that makes sense and we should investigate that with our kernel
team in the near future. I'm going to open a thread on it.
The guarantee with /etc/machine-id is really that it is valid at *any*
time, in early boot and late boot and all the time in between.
I think I will go that path which is an interesting one and mapping some of
my thoughts. Thanks for the guidance and documentation on what's the right
approach to achieve this race-free! I'll work on something around that and
propose a patch.
Looking forword to it.
Here we go :)
I did some factorization to reuse some functions on the first path and
added the binary helper, unit and man page.
It should follow your advice and be race-free. Tested various cases locally.
Cheers,
Didier
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