[systemd-devel] _netdev for system root mount?

[Thomas Blume]

On Mon, 16 Mar 2020, Mantas Mikulėnas wrote:

> On Mon, Mar 16, 2020 at 11:52 AM Thomas Blume <Thomas.Blume at suse.com> wrote:
>       On Fri, 13 Mar 2020, Alexander E. Patrakov wrote:
>
>       > On Fri, Mar 13, 2020 at 7:07 PM Andrei Borzenkov <arvidjaar at gmail.com> wrote:
>       >
>       >> And what is the "official" way to prevent various units required by root
>       >> mount from being stopped during shutdown? There could be arbitrarily
>       >> deep stack (NIC - iSCSI - multipath - raid - lvm - crypto - ...).
>       >
>       > https://systemd.io/ROOT_STORAGE_DAEMONS/
>
>       So, that means that the iscsi unit files in the running system are not
>       designated and supported for system root, right?
> 
> 
> I've only used iSCSI for data volumes, but... how could the rootfs possibly be dependent on a process running *from the same rootfs*? I mean, the iSCSI or NBD daemons have to start from
> somewhere else *before* the rootfs is set up and mounted, don't they?
> 
> If the rootfs is iSCSI-based or NBD-based, then I would expect the corresponding daemons to be started from the *initramfs*, meaning they wouldn't be managed as rootfs .service units in
> the first place -- and they wouldn't be stopped along with other .service units either.
> 
> (Note that if your initramfs itself is systemd-based, then it has a completely separate set of units, with its own boot order and everything.)
>  
>
>       What about the network.service?
>       I guess this should be also unsupported for the network device providing system
>       root?
> 
> 
> network.service is a distro-specific addition. I don't know what it supports on your system.
> 
> But in general, network configuration tools often have an option to leave an interface configured upon exit. For example systemd-network has KeepConfiguration=.
>  
>
>       Finally, can I also conclude that the _netdev parameter as an ordering
>       constraint for the network block device is also not supported for system root?
> 
> 
> Same comment as above... how is systemd supposed to put other units before the rootfs, if they're started *from* the rootfs?

I see the logic, thanks.
Still, I think ths should better be documented, at least for the _netdev parameter.


Best regards
Thomas Blume

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