!I recovered the diary
 --- 
agk's diary 
5 August 2026
 ---
written on HP 200LX (1994) with Memo editor
in coffee shop
 --- 
I recovered my daughter's diary and my to-do list
from the SvarDOS USB. Thanks for the emails, Ben
Collver's textfile on gopher, and response to my 
post on sdf's bboard!

What I think is so cool about the data recovery: I
did it on the same diskless HP Mini netbook that the
SvarDOS USB stick was in when it was corrupted!

Recap: I'm testing using DOS from USB sticks for
everyday salvage computing tasks: edutainment wares
for my daughter and her friends, writing and editing
wares for her and I. Each system has a focused 
purpose; you change activities by swapping USB 
sticks (which could, conceptually, be floppy disks,
ROM carts, CF cards, or SD cards).

The benefits of DOS were immediately apparent: DOS
boots instantly, it has a better selection of high-
quality educational and writing wares than Android/
iOS, Win 10/11, OSX, or Linux/BSD, and it's simple 
and comprehensible by mere mortals.

Drawbacks took time to show. If the OS boots to RAM
and discards changes at shutdown, it's unbreakable, 
but no good for saving writing, drawings, musical
compositions, or game progress. That's the approach
of the FreeDOS-based FUZUMA children's system-on-a-
stick by Paul Blair.

My SvarDOS system-on-a-stick is for writing, so it
takes a different approach, with different drawbacks.
I modified it slightly from Liam Proven's usb-dos.
Nothing is read-only. Plugged into a host system,
it's mass storage. You can break any part of the
system when booted or accessed as mass storage.

The system lost power while booted, with a file open
in an editor, Two directories were corrupted and
became unreadable: the DOCS directory, where all 
textfiles on the system lived, and UTIL directory,
where the editor I was using (calvin VI) lived.

Since those folders were garbled trash, when viewed
as mass storage with diskrescue software, and the
system-on-a-stick no longer booted, instead I booted
an AntiX system-on-a-stick in the HP Mini netbook
the SvarDOS system-on-a-stick had been in. I plugged
in the broken SvarDOS usb and located it with lsblk.
It's /dev/sdc, with one partition, /dev/sdc1.

dd if=/dev/sdc of=/home/dos/img copied all 692 MiB
on the drive into one file.

hexdump is a hex viewer I found by searching for 
"hex" in /bin, /usr/bin, and /usr/sbin. The options
confused me, but the manpage said if you call it as
hd it will have sane defaults.

hd /home/dos/img | grep Unique searched the hex dump
for "Unique" (I used a different string I suspected 
was unique to the text files I wanted to recover). 
It turned up three lines containing the unique ascii
string.

Each line of the hex dump was numbered. I searched
the number of each line I turned up minus the last
two digits with grep, and found the group of 16 
lines that contained it. I incremented and decrement-
ed my search until I found the whole lost diary, and
wrote it down with pencil. I found my todo list the
same way.

Then I tried dosfsck on the usb stick, which didn't
fix it. So I checked it for bad sectors with rufus
on Windows 10, re-imaged it with Rufus, booted it,
re-typed the two lost files, shut it down, and 
copied them to a Windows system.

A better online backup workflow, possibly to a D:
partition on the bootable stick, is a project for
another day.

 ---
Notes from correspondents:

Ben Collver (via gopher): By default SvarDOS uses a
   synchronous filesystem without disk cache.  So i
   am guessing the power was pulled while the editor
   was running and still had a file open.

   To recover the corrupted data, i would probably 
   plug the USB key into a Linux box, use the `dd`
   command to get an image, and then use the
   `strings` command to rip the text content out of
   that image.  Then i'd search for known text.  
   With luck, FAT fragmentation won't be too bad, 
   and recovering some data might be possible.

sjlawson (via bboard): Back in the DOS days I used
   to use a hex editor to recover corrupted files
   and edit data in ram to cheat on the game,
   Frontier (ELITE II), to get Thargoid lasers on a
   relatively tiny Viper MK-II spaceship :)

J.M.C.S. (via email): Try...ddrescue:
   gnu.org/software/ddrescue/manual/ddrescue_manual.html
   Something like:
   ddrescue /dev/sdc hdimage mapfile
   (if your usb drive was /dev/sdc) could be a good
   starting point.

The Free Thinker (via email): TestDisk and PhotoRec
   are the standard tools for this, and they still
   release versions for DOS:

   cgsecurity.org/wiki/TestDisk
   cgsecurity.org/wiki/PhotoRec

   TestDisk is fairly automatic although it can
   still be a little confusing.... Failing that,
   PhotoRec recovers individual files, but often
   without the filenames. Also you need to write the
   files it recovers to a different drive than the
   one you're recovering from.

   DOS filesystems shouldn't care about having power
   cut...unless it happened at the moment of a save 
   operation. Perhaps the USB drive was doing some 
   reorganising...when the power was cut, which 
   wouldn't necessarily be limited to the partition 
   which was being changed? Anyway DOS (or...MSDOS)
   ...doesn't do writes to any system files in C: of
   its own accord, so it's only programs you run and
   save things from which will do writes - usually
   pausing briefly while they do it. Consider too
   that the USB drive might have developed a fault.