[systemd-devel] [HACK/RFC/PATCH] systemd-su: "su" on steroids

[Shawn Landden]

On Tue, Dec 10, 2013 at 3:18 PM, Lennart Poettering
<lennart at poettering.net> wrote:
> On Mon, 02.12.13 21:47, David Herrmann (dh.herrmann at gmail.com) wrote:
>
>>
>> 4h later, I present "systemd-su":
>>
>> If you want to give it a try, run:
>>   systemd-su -u david /bin/sh
>>
>> It requires the systemd-suexec helper internally, so if you didn't install
>> it, use something like this:
>>   SYSTEMD_SUEXEC=/home/david/dev/systemd/systemd-suexec ./systemd-su -u david sh
>> Otherwise, systemd-su cannot find the systemd-suexec binary.
>
> Hmm, if we allow that "su -" tells logind to create an entirely new
> session even when called from an existing one, do we still need
> "systemd-su"? That should be pretty close, no? That sounds easier to
> do...
>
>> Additionally, I create an anonymous AF_UNIX socket in systemd-su which
>> systemd-suexec connects to. I then pass file-descriptors to systemd-suexec
>> which installes them as STDIN/OUT/ERR.
>> I actually think it would be quite useful to extend the
>> StartTransientUnit() dbus call to allow passing FDs. It would allow us to
>> "store" FDs with active units, which would be useful for a lot of other
>> concepts (like storing DRM framebuffer handles..).
>
> Hmm, so we thought about adding support for something like a per-service
> fd storage facility in systemd. This would be populated from the .socket
> units, but could also be passed in for transient units by the caller or
> even updated by the services themselves if they want to store additional
> fds in systemd. This would solve a number of issues for us, including
> one big one: currently if you restart systemd-journald you lose the
> per-service stdout/stderr connections because there's no way to save
> them.
We need to do this in order to integrate criu into systemd as well.
>
> Lennart
>
> --
> Lennart Poettering, Red Hat
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