Starting programs before udev is running

Starting programs before udev is running

[Demi Marie Obenour]

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Is it dangerous to start programs before udev is running,
so long as all of the other dependencies of these programs
(such as /var and /home being read-write) have been satisfied?
Or do programs assume that udev has actually started, not
merely bound to its sockets connections?

The reason I ask is that I'm using systemd-udevd with a
non-systemd service manager (s6 + s6-rc) and it has an
incompatible method for readiness notification (writing
a newline to a file descriptor).  s6-rc has full support
for dependencies, so I can easily have udev write to a FIFO
when it picks up /dev/zero and have other things depend on
that, but I'm curious if there are any other problems with
this approach.

In case it matters, the only programs running on the machine
will be some VMs, a few programs to support them, a Wayland
compositor (now Weston, eventually COSMIC), some XDG portals,
and possibly a couple of others.  No code not included in the
(signed and dm-verity protected) root filesystem will be
allowed to execute.
-- 
Sincerely,
Demi Marie Obenour (she/her/hers)

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Re: [systemd-devel] Starting programs before udev is running

[Barry Scott]

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> On 2 Sep 2025, at 10:09, Demi Marie Obenour <demiobenour@gmail.com> wrote:
> 
> The reason I ask is that I'm using systemd-udevd with a
> non-systemd service manager (s6 + s6-rc) and it has an
> incompatible method for readiness notification (writing
> a newline to a file descriptor).

Two thoughts.

Wrap in a program that converts the none-systemd notifications into the systemd one?

Patch in the systemd notitification, which is easy to do?

Barry


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