add blog entry 129

content/index.md

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 This blog is maintained by [Gibheer](/author/Gibheer) and [Stormwind](/author/Stormwind)
 about various topics.
 
+ * [dual boot with root on ZFS](post/129.html)
  * [leaving FreeBSD for Archlinux](post/128.html)
  * [link summary 2016/07/08](post/127.html)
  * [poudriere in jails with zfs](post/126.html)

content/post/129.md

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++++
+title = "dual boot with root on ZFS"
+date = "2023-09-17T20:00:00+00:00"
+author = "Gibheer"
++++
+
+Some time ago I was experimenting on a server with dual booting FreeBSD
+and Linux from the same ZFS pool.
+
+The idea was, that I could allocate the space dynamically instead of using hard
+partitions and wasting valuable disk space.
+
+As of writing, ZFSonLinux and FreeBSD use different mechanisms to figure out
+which partition to mount as the root partition. And this is what makes the dual
+boot possible at the end.
+
+The following description uses only EFI. I have no idea if this also possible
+with other boot managers.
+[systemd-boot](https://www.man7.org/linux/man-pages/man7/systemd-boot.7.html)
+serves as the boot manager.
+
+disk layout
+-----------
+
+The disk must contain a EFI system partition and the rest will be made available
+for ZFS.
+
+* /boot FAT32 512MB to 1GB
+* zpool zfs
+
+zpool settings
+--------------
+
+Some care must be taken with enabling features on a ZFS pool, because each
+kernel must be able to understand the flags.
+For example the ZFS version of a CentOS7 might not be able to use lzma
+compression. In that case the ZFS driver will just not mount the partition
+and you might end up with that distribution unbootable.
+
+For FreeBSD to be able to boot, the partition must be set as the boot target
+directly on the zpool like:
+
+```
+zpool set bootfs=rpool/ROOT/freebsd rpool
+```
+
+zfs partitions
+--------------
+
+I have used rpool/ROOT as the partition for all OS partitions, so I ended up
+with:
+
+  * rpool/ROOT/archlinux
+  * rpool/ROOT/freebsd
+
+To make things easier I set the following flags on `rpool/ROOT`:
+
+  * compression=on
+  * atime=off
+  * acltype=posix
+  * relatime=on
+  * canmount=noauto
+
+This way all OS partitions get the same attributes and I don't have to remember
+to set it after creating a new OS tree.
+
+systemd-boot
+------------
+
+As for the boot entries I have used systemd-boot and its easily to modify
+loader entries.
+
+For FreeBSD my loader entry looks like
+
+```
+title FreeBSD
+efi /freebsd.efi
+```
+
+where I have copied the freebsd.efi file directly into /boot.
+FreeBSDs actual /boot partition resides in its partition rpool/ROOT/freebsd.
+
+For my archlinux I use the lts kernel to avoid breakage with new kernel releases
+which results in the following entry
+
+```
+title Archlinux
+linux /vmlinuz-linux-lts
+initrd /initramfs-linux-lts.img
+options zfs=rpool/ROOT/archlinux rw
+```
+
+installation process
+--------------------
+
+As for the installation process, I first installed archlinux. After that was
+up and running, I installed FreeBSD via downloading the base.txz and unpacking
+it into its own partition.
+
+Apart from the default adjustments to /etc/rc.conf and setting a root password
+nothing further was needed to properly boot the system.
+
+documentation
+-------------
+
+There is some really good documentation for the details out there, for example
+
+* [systemd-boot on Archlinux wiki](https://wiki.archlinux.org/title/systemd-boot)
+* [the archzfs project](https://github.com/archzfs/archzfs)
+* [the mfsbsd scripts](https://github.com/mmatuska/mfsbsd)
+* [FreeBSD handbook](https://docs.freebsd.org/en/books/handbook/zfs/)
+* [ZFS man pages](https://github.com/openzfs/zfs/tree/master/man)
+
+And please do not forget to read the man pages. ZFS and systemd have some really
+wonderful man pages with tons of knowledge put into them. In most cases there
+are even some examples at the end.
+
+Enjoy and have fun.