Hi Karl,

On 26/5/22 13:26, karl@??? wrote:
> And, if DEVTMPFS isn't used then udev will not start, don't know
> about eudev.
> vdev and mdev will probably run fine without devtmpfs.

Vdev does work without DEVTMPFS. Indeed, i have the following lines in my initramfs:

if command -v udevd; then
    mount -t devtmpfs -o nosuid,mode=0755 udev /dev
else
    mount -t tmpfs -o nosuid,mode=0755 none /dev
fi

leading to something like this in my /etc/mtab:

    none /dev tmpfs rw,relatime,size51200k,mode755 0 0

in contrast to

    udev /dev devtmpfs rw,nosuid,relatime,size=.....

I did build a kernel without devtmpfs support:

https://www.gnuinos.org/nodevtmpfs/ <https://www.gnuinos.org/nodevtmpfs/>

but don't expect to get eudev working with it.

On the other hand, and just the same as vdev, you don't need devtmpfs to run mdev:

https://sunxiboards.wordpress.com/2013/09/23/using-devtmpfs/ <https://sunxiboards.wordpress.com/2013/09/23/using-devtmpfs/>

Calling `|mdev -s`| will check /sys and will create the correct devices. Therefore,
if you don't use devtmpfs, you need to call `mdev -s` in your /bin/init script to
populate /dev.

And then, when the kernel detects a new device, it calls the already mentioned

/proc/sys/kernel/hotplug

Cheers,

Aitor.