[arch-releng] [RFC] Switch from dm-snapshot to overlay

Gerardo Exequiel Pozzi vmlinuz386 at gmail.com
Thu Jul 30 13:48:53 UTC 2015

On 07/30/2015 06:53 AM, Christian Hesse wrote:
> Gerardo Exequiel Pozzi <vmlinuz386 at gmail.com> on Sat, 2015/07/18 18:18:
>> Hello
>> Guys, what do you think about switching to overlay filesystem by
>> default? This is already implemented around Jan 2015 of this year.
> I do not care and I am fine with either of both.
> For my own project I do use one of both, depending on what matches my use
> case. So please keep support for dm-snapshot in archiso.

Yes there are no plans in removing it.

>> Why?:
>> * It seems the most "natural" way.
>> * Low RAM usage if user wants do to some changes inside live-enviroment.
>> * No crazy crashes if zero-free-space is reached (some bbs/wiki talks
>> posts ask about this)
>> There is at least two issues at boot time:
>> (1) /var/log/journal: Cannot set file attribute for '/var/log/journal',
>> value=0x00800000, mask=0x00800000: Inappropriate ioctl for device
> Looks like overlayfs is missing some features compared to ext4 and friends.
> We had some changes in systemd about filesystem features lately, so is this
> still true?

Should be fixed (read hidden), by latest 223 version.

> For live systems I tend to set some more journal configuration... What about
> adding something like this in /etc/systemd/journald.conf:
> [Journal]
> Storage=volatile
> SystemMaxUse=8M
> RuntimeMaxUse=8M

No problem, go ahead ;)

>> (2) /etc/machine-id: Failed to unmount transient /etc/machine-id file in
>> our private namespace: Invalid argument

About this, I opened an issue here [#1] with some interesting comments
from devs.

> This happens even if you set the machine-id in initramfs. On an ext4-based
> machine I have:
> # systemctl status systemd-machine-id-commit.service
> ● systemd-machine-id-commit.service - Commit a transient machine-id on disk
>    Loaded: loaded (/usr/lib/systemd/system/systemd-machine-id-commit.service; static; vendor preset: disabled)
>    Active: inactive (dead)
> Condition: start condition failed at Thu 2015-07-30 08:29:45 CEST; 3h 19min ago
>            ConditionPathIsMountPoint=/etc/machine-id was not met
>      Docs: man:systemd-machine-id-commit.service(8)

I do not see the relation here, no errors. In you case looks like not

Thanks for your feedback Chris :)

[#1] https://github.com/systemd/systemd/issues/729

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