Other HOWTO share labeled swap between FreeBSD & Linux

[rbranco]

EDIT:

Now it's possible to do it in -CURRENT.

Just run `echo geom_label_load='"YES"' >> /boot/loader.conf` as root, reboot and use whatever GEOM detects as swap in /dev/swaplinux.

On -STABLE you have to apply the diff in https://github.com/freebsd/freebsd-src/pull/1205 like this:

cd /tmp
fetch https://github.com/freebsd/freebsd-src/pull/1205.diff
cd /usr/src
patch -p1 < /tmp/1205.diff

 

[cy@]

You can't unless you run mkswap on Linux before using it. If FreeBSD writes to the swap partition the Linux swap metadata will be destroyed or corrupted making it unusable by Linux. To get around this you'll need to create a systemd service to mkswap the swap partition and enable it.

FreeBSD, like all other UNIX/UNIX-like variants except for Linux simply uses swap without swap metadata. Linux needs its swap metadata in order to use swap.

 

[rbranco]

You can't unless you run mkswap on Linux before using it. If FreeBSD writes to the swap partition the Linux swap metadata will be destroyed or corrupted making it unusable by Linux. To get around this you'll need to create a systemd service to mkswap the swap partition and enable it.

This is not really needed anymore with this workaround that prevents the metadata from being overwritten.

But even without this patch, swapon calls mkswap if needed as you can see here. Only labeled swap in /etc/fstab would be unusable without this workaround.

 

[cracauer@]

Actually, the partition marking that Linux does is an excellent idea. FreeBSD should use one, too, and there is no reason to use a different on-disk format than Linux.

 

[rbranco]

swapon shall not overwrite the header!

swapon: Do not overwrite Linux swap header

swapon: Do not overwrite Linux swap header by ricardobranco777 · Pull Request #1084 · freebsd/freebsd-src

The Linux swap partition uses a 4096-byte header that holds the label & UUID. You can see the structure here. The problem is thus how to prevent FreeBSD from overwriting the header. It turns out th...

github.com

Hope I'm not breaking any rule wrt shameless self-promotion. I just want people to test it lol.

 

[Cath O'Deray]

a PR

Gentle hint: in the sidebar, "Experimenting with 'simple' pull requests…"

More specifically (unfortunately, the top level README lacks a link to this GitHub src-specific file):

freebsd-src/CONTRIBUTING.md at main · freebsd/freebsd-src

The FreeBSD src tree publish-only repository. Experimenting with 'simple' pull requests.... - freebsd/freebsd-src

github.com

 

[rbranco]

Also possible on NetBSD: https://github.com/NetBSD/src/pull/33

Not needed at all since NetBSD skips the first page.

 

[gpatrick]

Don't put the Linux partition into hibernate while using the FreeBSD partition because Linux writes to swap on hibernate, and FreeBSD would overwrite that.

 

[rbranco]

Don't put the Linux partition into hibernate while using the FreeBSD partition because Linux writes to swap on hibernate, and FreeBSD would overwrite that.

How is that possible in a dual boot environment?

 

[rbranco]

Edited the original post to reflect the new procedure now that https://github.com/freebsd/freebsd-src/pull/1205 was merged.