[SOLVED] Difficulty Mounting ext3 partition in OpenBSD 6.4

jhumphrey · 01-10-2019, 02:47 PM

Hi All,

I am currently dual-booting (soon to be triple booting) a laptop between Linux and OpenBSD.

I have Linux installed on an ext3 partition, and I want to access this partition in OpenBSD.

So I first ran

Code:

fdisk sd0c

which output something like the following:

Code:

# ID ...
0 83 ...  (Linux)
1 83 ...  (Unused)
2 A6 ...  (OpenBSD)
3 82 ...  (swap for Linux)

So I try to mount the first partition (Here's where I think the problem is)

Code:

# mkdir /mnt/sda1
# mount -t ext2 /dev/sd0a /mnt/sda1
Device Busy

So I look in /etc/fstab

there are three entries, one for the swap, one for /, and one for /home

So I think that sd0a, sd0b, and sd0d are the OpenBSD partitions, while sd0c points to the entire disk.
does this make sense? if so, where do I find my Linux partition?

If this is a dumb question, where would be a good place for me to look in the man pages?

I tried fdisk(8), and mount(8), and the openBSD FAQ

multios · 01-10-2019, 09:44 PM

First off, welcome to linuxquestions

If I read correctly what you wrote, you are trying to mount the / partition

To see which partition OpenBSD has labeled for linux, run as root: disklabel -p sd0 or perhaps /dev/sd0...if that's the harddrive you are using.
That will show you which partition to try and mount. So then you might, as an example write as root mount -t ext2fs /dev/sd0h /mnt.
Also, it may also have to be mounted read only, so then you type mount -r -t ext2fs /dev/sd0h /mnt

I can't run OpenBSD on this particular laptop, which makes my blood boil, so I'm going by memory.

HTH

cynwulf · 01-11-2019, 07:17 AM

Quote:

Originally Posted by jhumphrey

So I first ran

Code:

fdisk sd0c

which output something like the following:

Code:

# ID ...
0 83 ...  (Linux)
1 83 ...  (Unused)
2 A6 ...  (OpenBSD)
3 82 ...  (swap for Linux)

So I try to mount the first partition (Here's where I think the problem is)

Code:

# mkdir /mnt/sda1
# mount -t ext2 /dev/wd0a /mnt/sda1

You're also examining the MBR of sd0 with fdisk but then trying to mount a partition of wd0.

jggimi · 01-11-2019, 09:30 AM

Quote:

Originally Posted by cynwulf

You're also examining the MBR of sd0 with fdisk but then trying to mount a partition of wd0.

This. wd0 and sd0 are two different drives.

jhumphrey · 01-11-2019, 09:58 AM

oops...
I am writing this on the Linux side, so I mounted sd0a NOT wd0a... typo.
I will try out your advice, and write back.

jhumphrey · 01-11-2019, 11:32 AM

I was not clear enough in my first post, sorry.
So I am trying to mount my Linux partition from inside OpenBSD, and cannot find it.
I did a little research online and found that in FreeBSD I would look for something like ad0s1.
I could not find it, or sd0s1, so maybe OpenBSD uses a different system.
I guess it's time to dig into the FAQ again...

@multios, I tried running disklabel, It just gives me the OpenBSD partitions.
BTW are you sure it's disklabel -p?

jggimi · 01-11-2019, 02:29 PM

Let's start with some level-setting. Let us assume, for right now, that you only have one physical disk drive, and you are using an architecture such as amd64 or i386 that boots with either MBR or GPT partitioning.

On OpenBSD, this drive would be either "wd0" or "sd0". wd(4) is the driver for IDE/PATA drives, while sd(4) is the driver for SCSI/SATA/USB drives. Disklabel partitions begin with "a" and end with "p", such as sd0h or wd1a.
There are two levels of disk partitioning. 1) MBR/GPT partitions, and 2) OpenBSD disklabel partitions. The single OpenBSD MBR/GPT partition is subdivided into multiple disklabel partitions.
When OpenBSD is first connected to a disk drive, and there is no on-disk OpenBSD disklabel already present -- OpenBSD will scan the MBR/GPT partition table and look for any pre-existing, recognized "foreign" MBR/GPT filesystem. It will build a virtual disklabel, pre-populated with any of these recognized filesystems, starting with disklabel partition letter "i". If there is already an OpenBSD disklabel on-disk, it will not scan the MBR or GPT partition table, and will only use what it finds on the on-disk disklabel. Therefore, if you have pre-existing MBR/GPT partitions, OpenBSD will find them when first installed. If you created these MBR/GPT partitions AFTER OpenBSD has written its disklabel, you must add these partitions to the disklabel manually.

jhumphrey · 01-14-2019, 09:22 AM

Thanks, @jggimi.
This helps clear up a lot of confusion.
I installed Linux before installing BSD, and because I formatted its partition as an ext3 instead of an ext2 it was not recognized, and thus not added to the disklabel.
Am I correct?

jggimi · 01-14-2019, 10:53 AM

No, that's not the reason. EXT3 is EXT2 plus journaling. OpenBSD ignores journaling and treats the filesystem as EXT2. The apparent reason for failure to mount appears to be improper nomenclature in your mount command.

You have stated that the Linux partition was first-on-disk before OpenBSD was installed. If that is true, then there should be an "i" disklabel partition created when OpenBSD did not find a pre-existing disklabel, and scanned the MBR or GPT.

Your mount command should be one of these two commands, depending on whether the drive is EDI/PATA or SCSI/SATA/USB.

Code:

# mount -t ext2 /dev/wd0i /mnt

or

Code:

# mount -t ext2 /dev/sd0i /mnt

I have intentionally NOT added your directory "sda1" as a mount point because you are already confused about OpenBSD disk drive nomenclature, and I recommend you not use Linux nomenclature which does not apply on OpenBSD systems.

jhumphrey · 01-17-2019, 10:17 AM

I solved the problem, with all of your help.
My Linux partition was not in the disklabel, so I edited the disklabel, and I can mount now.
Thank you for all your help.

P.S. I changed the name of the mount point from sda1 to Linux.
P.P.S OpenBSD has great documentation, better than Linux IMHO.

jggimi · 01-17-2019, 12:54 PM

Glad you got the problem resolved!

Quote:

Originally Posted by jhumphrey

My Linux partition was not in the disklabel...

As noted earlier, that will happen when an OpenBSD disklabel is stored on disk before the Linux partition is installed.

There are two OTHER ways this might have occured: either a custom partitioning schema was deployed during installation, or, more likely, OpenBSD was re-installed and the partition not retained during re-installation.