Solved Is it still possible to downgrade the root filesystem to read-only?

[cracauer@]

Is it still possible to downgrade the root filesystem to read-only?

`mount -u -o ro /`
gives me
mount: /dev/gpt/rootfs: Device busy

 

[VladiBG]

Just an idea:
check the current locked files using procstat

 

[MG]

I tried mkdir /tmp/a && mount_nullfs / /tmp/a && mount_nullfs /tmp/a /
Instant hard reset. It wasn't even read-only yet.

 

[cracauer@]

Just had to add -f, then it works.

 

[bakul]

Go single user (kill -TERM 1) first if you don't want to force mount readonly.

 

[Beastie]

Just had to add -f, then it works.

Yikes! You chose the dirtiest method. At least try logging off any logged-in user in case your blockage problem is caused by some active user process. And if the problem, whatever it is, is still not fixed, try going single user. Hopefully this will properly sync everything (write caches) that needs syncing and avoid data corruption/loss and process crashes.
By the way, umount(8) says -f [...] The root file system cannot be forcibly unmounted, so I don't what's happening (or not happening) here.

Go single user (kill -TERM 1) first if you don't want to force mount readonly.

# shutdown now is considered to be a more graceful method.

 

[cracauer@]

I need the system in multi user mode with me logged in.

The background is that I do very panic()iky kernel work and don't want to go through fsck when I reboot.

 

[ralphbsz]

Use ZFS for the root file system? No fsck required. But you're probably interested in the leanest and fastest system.

 

[cracauer@]

Use ZFS for the root file system? No fsck required. But you're probably interested in the leanest and fastest system.

Ohhh, I would be very afraid that I damage a ZFS by doing the panic thing often. At some point the lack of fsck can turn into a disadvantage. Resource wise I could handle it.

 

[MG]

I need the system in multi user mode with me logged in.

The background is that I do very panic()iky kernel work and don't want to go through fsck when I reboot.

Maybe a stripped down install that takes everything via nfs... Make a 1st image and when things go wrong, overwrite the partition with the original again. A basic FreeBSD system is +/- 450MB. You can still make a lot of it remote. I think 200MB for the entire system must be possible. That's a few seconds recovery.

 

[cracauer@]

Maybe a stripped down install that takes everything via nfs... Make a 1st image and when things go wrong, overwrite it with the original again. A basic FreeBSD system is +/- 450MB. You can still make a lot of it remote. I think 200MB for the entire system must be possible. That's a few seconds recovery.

Unfortunately all my attempts to do PXE boot in bhyve have failed. Bhyve only has uefi now, and it doesn't contain any PXE implementation. You can bring up iPXE, but that one refuses to accept dhcp reply network packages for reasons unknown.

 

[bakul]

# shutdown now is considered to be a more graceful method.

That doesn't bring the system down to single user mode. Also note that (from a FS perspective) reboot is good enough now (instead of "shutdown now").

 

[Beastie]

That doesn't bring the system down to single user mode.

I've used it for just that for years. And the Handbook seems to agree:

15.2.4.1. Single-User Mode
[...] It can also be reached by running shutdown now from multi-user mode.

 

[bakul]

Seems strange that shutdown without options doesn't actually shut the system down!

From its man page:

The shutdown utility provides an automated shutdown procedure for super-
users to nicely notify users when the system is shutting down, saving
them from system administrators, hackers, and gurus, who would otherwise
not bother with such niceties.

Since there are no other users on my machines and since it splats a message on every logged in virtual terminal I usually don't bother with it!

 

[hedwards]

Seems strange that shutdown without options doesn't actually shut the system down!

From its man page:

Since there are no other users on my machines and since it splats a message on every logged in virtual terminal I usually don't bother with it!

Is it? It's been a while since I actually did that, but wasn't the purpose of that getting to single user mode if for some reason you want to do so before/without rebooting? It seems sensible enough to me that it would default to the thing that's the least likely to cause extra problems as you can still shutdown or reboot from there without an real headaches.