Initramfs with a long-running service

[rikonor]

Hi,

I am attempting to create an initramfs that instead of mounting another file-system will have a binary included in it (e.g an HTTP server) that is then started once the initramfs has finished.

This service will then continue running (essentially forever) - I was curious if anyone has done this before, and if so if they can provide any guidance on how to do this.

[LaszloGombos]

In the kernel command line

• do not specify root=
• specify init=yourservicebinarypath

Not a common use-case but you might be able to make it work. I have not tried. Not sure what you mean by "initramfs has finished" as I think you need to basically stay in initramfs.

Some Linux distributions configured to stay in initramfs - e.g. http://tinycorelinux.net

From http://tinycorelinux.net/corebook.pdf

it never leaves the first stage. We fully run in the initial RAM disk, never leaving for a spinning disk (or a network mount, etc).

[rikonor]

Hi @LaszloGombos - thanks for the info! I think I was overcomplicating things a bit. I probably don't need a tool like dracut for this. What I ended up doing which seems to work fine is:

1. Get a basic Alpine filesystem (I did this by grabbing an official Alpine Docker image and extract the filesystem from it).
2. Inject my binary into this filesystem.
3. Inject an /init script that brings up the network and then starts my long-running binary.
4. Create a cpio archive from this filesystem.

I then can start the whole thing with qemu by specifying a kernel and the resulting initramfs.