[yocto] /var/volatile not mounted as tmpfs on read-only rootfs when migrating to Warrior

[Ryan Harkin]

Hi Carsten,

Thanks for your help.

On Fri, 2 Aug 2019 at 20:42, Stelling2 Carsten <
Carsten.Stelling2 at goerlitz.com> wrote:

> Hi Ryan,
>
>
>
> Regarding to timesyncd, have a look at
> https://wiki.archlinux.org/index.php/systemd-timesyncd, especially the
> section
>
> “Note: The service writes to a local file /var/lib/systemd/timesync/clock
> with every synchronization.
>
> This location is hard-coded and cannot be changed. This may be problematic
> for running off
>
> read-only root partition or trying to minimize writes to an SD card.”
>

Yes, this looks like it is my problem. I experimented with timesync, and by
making /var/lib and a few other places writable, I'm able to start it
manually, but not via systemd, which I think is experiencing other issues
with the read-only rootfs.


>
> See also https://github.com/systemd/systemd/issues/5610 for your problem
> with systemd-resolved.
>
> According to this, /var, /var/tmp, /run, and /tmp should be writable.
>
I think the problem is not Yocto specific, but possibly I overlook
> something.
>

Again, I think you're right. I need to have these areas writable from boot.
But I don't know how.

I  suppose my problem is that these areas used to be writable when I was
using Sumo, but moving to Warrior has caused something to change. I'm
wondering what extra steps I need to do in Warrior to ensure that all these
things are mounted with tmpfs as before. I expect my Sumo recipes worked
through luck more than design, and now something has changed, I need to
improve them.

It is rather difficult to work out what the relevant changes are.

Kind regards,
Ryan.


>
> Best regards,
>
>
>
> Carsten
>
>
>
> *Von:* yocto-bounces at yoctoproject.org [mailto:
> yocto-bounces at yoctoproject.org] *Im Auftrag von *Ryan Harkin
> *Gesendet:* Freitag, 2. August 2019 13:09
> *An:* yocto at yoctoproject.org
> *Cc:* openembedded
> *Betreff:* [yocto] /var/volatile not mounted as tmpfs on read-only rootfs
> when migrating to Warrior
>
>
>
> Hi,
>
>
>
> I have a working system based on Sumo. The system boots with a read-only
> rootfs, then applies are read-write overlay for /etc.
>
>
>
> When I migrate to Warrior, systemd-resolved fails to start. If I mount the
> same rootfs via NFS, it starts and works fine.  systemd-timesyncd is also
> failing, but I haven't looked into that yet. It also works fine on the NFS
> mounted system.
>
>
>
> The resolve problem seems to be caused by two things:
>
>     - /var/volatile is read-only
>
>     - /run/systemd/resolve has the wrong ownership
>
>       drwxr-xr-x  2 systemd-network systemd-journal  80 Jul 12 16:23
> resolve/
>
>       I think this permissions problem may be a result of the
> /var/volatile mounting
>
>       problems; it looks fine on the NFS mounted system.
>
>
>
> If I manually mount /var/volatile (it's in fstab) and change the ownership
> on /run/systemd/resolve, the service starts just fine.
>
>
>
> I also notice that /tmp is not mounted at all, which may be related.
>
>
>
> Here are the various tmp mount points on my read-only rootfs:
>
>
>
> $ mount | grep tmp
>
> devtmpfs on /dev type devtmpfs
> (rw,nosuid,size=112036k,nr_inodes=28009,mode=755)
> tmpfs on /dev/shm type tmpfs (rw,nosuid,nodev)
> tmpfs on /run type tmpfs (rw,nosuid,nodev,mode=755)
> tmpfs on /sys/fs/cgroup type tmpfs (ro,nosuid,nodev,noexec,mode=755)
> overlay on /etc type overlay
> (rw,relatime,lowerdir=/tmp/lower/etc,upperdir=/tmp/upper/etc,workdir=/tmp/upper/work/etc)
> tmpfs on /run/user/0 type tmpfs
> (rw,nosuid,nodev,relatime,size=23840k,mode=700)
>
> On the NFS mounted system, I see these:
>
>
>
> $ mount | grep tmp
> devtmpfs on /dev type devtmpfs
> (rw,relatime,size=118180k,nr_inodes=29545,mode=755)
> tmpfs on /dev/shm type tmpfs (rw,nosuid,nodev)
> tmpfs on /run type tmpfs (rw,nosuid,nodev,mode=755)
> tmpfs on /sys/fs/cgroup type tmpfs (ro,nosuid,nodev,noexec,mode=755)
> tmpfs on /tmp type tmpfs (rw,nosuid,nodev)
> tmpfs on /var/volatile type tmpfs (rw,relatime)
> tmpfs on /run/user/0 type tmpfs
> (rw,nosuid,nodev,relatime,size=23840k,mode=700)
>
> As you can see, NFS has these extra mounts:
>
>
>
> tmpfs on /tmp type tmpfs (rw,nosuid,nodev)
>
> tmpfs on /var/volatile type tmpfs (rw,relatime)
>
>
>
> I've tried reverting a few commits that may be related, but I haven't had
> any luck working out things have changed, eg:
>
>
>
> c4acf1b531  2018-10-19  volatile-binds: use overlayfs if available
>              [Matt Hoosier]
>
>
>
> Advice would be appreciated. Are there any particular areas I should be
> looking to work out what's going wrong?
>
>
>
> Kind regards,
>
> Ryan.
> --
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