/usr/bin/sudo: Structure needs cleaning

Nextcloud version: 15.0.12 (I think)
Operating system and version: Raspian something or other
Apache or nginx version: Apache 2 is all I know
PHP version: roughly 7.03

I have no idea what I’ve got as I don’t know how to get the info from a remote ssh terminal.
I have had Nextcloud for a couple years, and have updated it when a new stable release comes out.
It now wants me to update to version .14.
I tried with the auto updater, but found my USB drive was full, so it failed at “Creating Backup”
I can see no way of deleting old backups from the web page, so did an ssh and attempted to

sudo rm -f /media/USBdrive/nextcloud-bkp_2017*

only to find it didn’t know where sudo was.
When I did:

/usr/bin/sudo rm /media/USBdrive/nextcloud-bkp_2017*

it said:

> -bash: /usr/bin/sudo: Structure needs cleaning

I’m guessing this is really serious.
So I powered down via the web page power button, removed the stick and deleted the 2017 files on my Ubuntu rig and stuck it back.

Great. It backed up (after several attempts) only to fail at the unpacking files bit (can’t remember the exact phrase, but after the validating zip file bit).
It came up with something about 3 files.
I gave up.

It now comes up on login with:

It looks like you are trying to reinstall your Nextcloud. However the file CAN_INSTALL is
missing from your config directory. Please create the file CAN_INSTALL in your config folder
to continue.

I can’t: No sudo
I can still talk to it via ssh, so if someone told me how to get the necessary inf, and where it would be, I can go in and get it.

I was able to get into logging once and got a shedload of:

You are using a fallback implementation of the intl extension. Installing the native one is
highly recommended instead. at /var/www/nextcloud/3rdparty/patchwork

Can’t. No sudo
I did try to paste the config file:

[ File ‘./config.php’ is unwritable ]

The upshot is it’s shagged.
But as I have 3 external drives, a static IP address, 18 users, etc, how can I save all that info?
I can get into the :4443 page, only to find permission is denied on everything, so that’s a bust.
ssh only and no sudo…
Can I remove the SD card, stick it in a card reader on my dektop and use e2fsk?

I have a big hammer.
Yours hopefully.

Well, thanks for nothing.
Since no-one answered, I had to go it alone.
I installed a new image, but it wouldn’t see the USB.
The first thing USB init does is wipe all the old configs.
I’ve lost everything.