M en/blog/2021-11-03-dualboot-linux-and-openbsd-with-grub.md → en/blog/2021-11-03-dualboot-linux-and-openbsd-with-grub.md

@@ -10,8 +10,6 @@
 i've been trying to dualboot openbsd with linux using grub on both bios and
 uefi machines and here's a solution that i've come up with.
 
-<!--more-->
-
 there are some guides about this on the internet, but there's no single guide
 that covers both bios and uefi. @rootbsd has a video where he shows how to
 do this, but his solution has one little disadvantage. he's specifying drives
@@ -22,54 +20,66 @@ (which happened).
 
 all partitions and drives have their unique identifier -- uuid. there's no
 direct way to specify uuid in grub configuration, but there is a workaround.
-
-grub manual describes the `search` command which has an option to set root
+grub manual describes the `search` command which has an option to set the root
 device if it is found. so we can use it for our purposes.
 
-## steps for dualbooting in bios/legacy mode
+## dualbooting in bios/legacy mode
 
-1. install linux system on one of your drives
+this guide assumes that you have two drives, one of which has linux system installed
+and another has openbsd installed.
 
-2. reboot and boot from openbsd install media and install openbsd to other drive
-or partition.
+on linux system, use commands like `blkid` or `lsblk -f` to get a list of drives with
+their uuids. there should be a partition with type 'ufs2' on a drive with openbsd installed.
+write down or copy uuid of that partition.
 
-3. reboot and login to your linux system
+depending on your linux distribution, you may have different options to edit
+the grub config file. many distributions provide `/etc/grub.d` directory, which
+has separate files that then get combined into `/boot/grub/grub.cfg`. if you have it,
+then you can edit the `/etc/grub.d/40_custom` file, which is a good place
+for custom boot options and such. if it is not your case, you can edit `grub.cfg` directly,
+but note that it may be overwritten on a system update.
 
-4. open a terminal and run `blkid` or `lsblk -f` to get an output partition
-uuids.
+add this to your grub config (`40_custom` or `grub.cfg`, see above):
 
-5. write the following at the bottom of `/etc/grub.d/40_custom`:
+```grub.cfg
 
-  ```grub.cfg
+menuentry 'OpenBSD' {
+	search -sun <UUID>
+	chainloader +1
+}
+```
 
-  menuentry 'OpenBSD' {
-      search -su --no-floppy *UUID*
-      chainloader +1
-  }
-  ```
+where \<UUID\> is the uuid of your openbsd partition (with type 'ufs2').
 
-  where *UUID* is the uuid of your openbsd partition (with type 'ufs2')
+you can review options for a `search` command in grub's info page,
+but basically they are needed to use uuid instead of drive number,
+to set the root variable and to avoid searching floppies (which is not required,
+but added just in case).
 
-6. run either `update-grub` or `grub-mkconfig` depending on what distribution
-you are using. consult your distro's wiki to find a way to update your grub
-configuration with recent changes.
+if you edited the `40_custom` file, don't forget to run `grub-mkconfig` or `update-grub`
+(check your distribution's manual on updating the grub configuration).
 
-7. now reboot and you should see an openbsd's boot option in grub menu.
+after rebooting, you should see openbsd boot option in grub menu.
 
-## steps for uefi system
+## dualbooting in uefi/gpt mode
 
-for boot in uefi mode there are few differences. after installing openbsd
-don't reboot, but choose **shell**. now cd into `/mnt` directory and
-download `BOOTX64.EFI` from your desired openbsd mirror. for example:
+openbsd creates few partitions if you choose gpt partitioning scheme during installation.
+one of these partitions has fat12 file system and is of our interest.
+on linux side you need to get its uuid.
+
+as with bios/legacy boot described earlier, you need to add a boot option to grub,
+but this time it's a bit different:
 
-```sh
+```grub.cfg
 
-# cd /mnt
-# ftp https://cdn.openbsd.org/pub/OpenBSD/7.0/amd64/BOOTX64.EFI
-# reboot
+menuentry 'OpenBSD' {
+	search -sun <UUID>
+	chainloader /efi/boot/bootx64.efi
+}
 ```
 
-after that the only other difference is that `chainloader` directive should
-be `chainloader /BOOTX64.EFI`.
+where \<UUID\> is the uuid of openbsd's fat12 partition.
+
+don't forget to update grub configuration if you edited `40_custom` file.
 
-all other steps are the same.
+this also works even if you used full-disk encryption on openbsd.