by Joshua Branson ? April 05, 2023
The end of my previous blog post was a bit of a cliff hanger:
I did have a great time the next day. I was hoping to automount my usb
stick on boot. So I added this beauty to my /etc/fstab.
sd1i /mnt/usb msdos rw 1 2
The next time I booted it threw me into a rescue shell with only / mounted.
This is the story of how I fixed a broken fstab on OpenBSD. The day began like any other. It was cold and dark as I arose to play with my new OpenBSD computer. It was time to reboot! That magical moment when OpenBSD relinks the kernel at boot. How cool is that?
My admiration for this world class operating continues to rise as it boots, and OpenBSD proudly slaps me in the face (I did not write down the OpenBSD error message, but this is essentially what it said):
mount cannot find device sd1i. You are now in a resque shell.
root>
Hmmm. Well that?s a bummer. It looks like I had told OpenBSD that that usb stick
was necesary for boot. I also did not have the usb stick plugged in, and OpenBSD
needed me to write /dev/sd1i not sd1i. It might be a good project idea to
add opendev support to OpenBSD?s mount. Any takers?
Anyway, to fix this, I attempted to delete that last line from /etc/fstab. I
tried to type out cd /etc/. Instead I got gibberish. Testing the keyboard a
bit, I noticed that the keyboard was in the qwerty layout. I use dvorak. And my
laptop keyboard physically shows a dvorak keyboard layout. It?s really hard to
type correctly on a keyboard when pressing ??,.pyf? is ?qwerty?. Well let?s
change my keyboard layout (notice that all commands below are run as the root
user. The # means you are running as a root user).
I painstakingly typed out the following command.
# wsconctl keyboard.encoding=us.dvorakAwesome, that is an improvement. Let?s change /etc/fstab. The following
commands did not work, because the shell could not find the binary:
nano /etc/fstabvim /etc/fstabvi /etc/fstab
Well that?s weird. Is /usr/bin not mounted?
# mount
/dev/sd1a on / type ffs (ro)Oh great! I only have / mounted! So my commands are limited, and / is
mounted read only. So even if I find a text editor that I can use, I cannot
modify /etc/fstab. How do I mount / read-write? According to the irc people
who helped me out, this is how: you update the mount information based on what
/etc/fstab says.
# mount -uvw /
# mount
/dev/sd1a on / type ffs (rw)Awesome, fstab is editable! I tried to edit /etc/fstab but vi was not
available, probably because vi is located in /usr, which is not yet mounted.
What I should have done was mount -U. This just mounts all mount points
listed in /etc/fstab. I did not read that option in the manpage yet. So I
decided to manually try to guess which filesytem was which.
Well let?s print out human read-able file sizes of my filesystem partitions and that will give me some clue which filesystem is which. (please note that I am intentionally removing the offsets).
# disklabel -h sd1
16 partitions:
# size offset fstype [fsize bsize cpg]
a: 1.0G 4.2BSD 2048 16384 12960
b: 8.0G swap
c: 931.5G unused
d: 4.0G 4.2BSD 2048 16384 12960
e: 19.5G 4.2BSD 2048 16384 12960
f: 30.0G 4.2BSD 2048 16384 12960
g: 1.0G 4.2BSD 2048 16384 12960
h: 20.0G 4.2BSD 2048 16384 12960
i: 3.0G 4.2BSD 2048 16384 12960
j: 6.0G 4.2BSD 2048 16384 12960
k: 300.0G 4.2BSD 4096 32768 26062Ok. Clearly the 300G is my /home. I can mount that now.
# mount /dev/sd1k /homeOk. How do I mount /usr so that I have text editors? I don?t really know which
partition is which. I guess I will just guess. Eventually I did correctly mount
/usr, so now I should have access to some text editors! So now I could edit
fstab.
# vim /etc/fstab
vim: unknown commandOk. vim is not installed. Let?s try vi.
# vi /etc/fstab
vi: unknown terminal typeSo vi doesn?t run on the console? That?s odd. Ok. Lets see what head
shows me:
# head /etc/fstab
5583d235b610c8a2.a / ffs rw,softdep 1 1
5583d235b610c8a2.k /home ffs rw,softdep,nodev,nosuid 1 2
5583d235b610c8a2.d /tmp ffs rw,softdep,nodev,nosuid 1 2
5583d235b610c8a2.f /usr ffs rw,softdep,nodev 1 2
5583d235b610c8a2.g /usr/X11R6 ffs rw,softdep,nodev 1 2
5583d235b610c8a2.h /usr/local ffs rw,wxallowed,softdep,nodev 1 2
5583d235b610c8a2.j /usr/obj ffs rw,softdep,nodev,nosuid 1 2
5583d235b610c8a2.i /usr/src ffs rw,softdep,nodev,nosuid 1 2
5583d235b610c8a2.e /var ffs rw,softdep,nodev,nosuid 1 2
5583d235b610c8a2.b none swap swHey would you look at that! There is no line with /mnt/usb. I should be able
to just overwrite fstab with the output of head. Please do NOT copy or
execute the following command:
# head /etc/fstab > /etc/fstabI wish I had read the irc chat before I had executed the above command. In the
words of a wise sage, ?the redirection happens before head runs, so you?ll just
get a blank file.? And that is exactly what happened. /etc/fstab was empty.
Now how do I mount filesystem partitions in the correct locations? ?Out of the
frying pan and into the fire.?
Some of the people on irc mentioned that /var/backups should have a copy of my
fstab. Unfortunately, that backup command had not run yet. This was a fresh
OpenBSD install afterall.
One of the people on the OpenBSD chat showed me this link, which was super helpful, because it shows you the default size of the various partitions that the auto installer sets up. With that information, I was able to re-mount all my various partitions. Then someone on irc chat gave me this beauty of a command:
# mount | awk '{ print $1 " " $3 " " $5 " rw 0 0"}' > /etc/fstabThat created my fstab for me! Let?s check it out!
# cat /etc/fstab
sd1.a / ffs rw 1 1
sd1.k /home ffs rw 1 2
sd1.d /tmp ffs rw 1 2
sd1.f /usr ffs rw 1 2
sd1.g /usr/X11R6 ffs rw 1 2
sd1.h /usr/local ffs rw 1 2
sd1.j /usr/obj ffs rw 1 2
sd1.i /usr/src ffs rw 1 2
sd1.e /var ffs rw 1 2
sd1.b none swap swHmm, well the mount options are absent, and it is NOT using UIDs?But this should be enough to boot into a complete system. So I rebooted. Upon reboot, I was able to change the mount points to UIDs and copy the proper mount options from my desktop OpenBSD. I then very quickly set up hotplugd, which I will explain next time. Until then!