Downgrading Synology DSM

We use Synology Diskstations at work, and recently (September 2017) we bought an extra one for an upcoming project. I figured I’d give DSM 6.2 beta a look while it wasn’t doing anything important, and then the world fell in on our heads (one of the other units started failing disks at random) and what had been a spare play unit became the main SR for our XenServer infrastructure.

As part of the recovery from that, we’ve just managed to downgrade DSM 6.2 back to DSM 6.1. It’s not something all that difficult to do, but it’s not all that well documented otherwise, so I thought I’d leave the procedure here for reference. Some understanding of Linux is necessary to do this.

Shout out to Darren D on YouTube: his one-and-only video (and doobly-doo) gave me the procedure. I’ve updated with DSM 6.1 versions of the files mentioned, but given he was talking about the DSM 6.0 beta on the video, I would expect this to work into the future. Watch the video before doing this, it’ll all make a lot more sense that way.

  1. Download the two latest DSM 6.1 firmware PAT files for your unit from the Synology website: 15217.pat and 15254.pat at the time of writing.
  2. Turn on the Synology and backup if needed; the array contents should survive this, but if your configuration is important, make a note of it all now, you’re about to nuke it.
  3. Create a shared folder (“test” on “volume1” is used in this guide).
  4. Using 7-Zip, extract four files from DSM 15217.pat (checksum.syno, grub_cksum.syno, rd.gz and zImage). Place these four files onto the shared folder.
  5. Enable SSH or Telnet in the DSM control panel.
  6. Using PuTTY, or another SSH/Telnet client, access the diskstation.
  7. Log in as an administrative user (“admin”).
  8. Type “sudo su”. The password it asks for is the same one as 7. above.
  9. Type “cd /dev” to change to the devices directory.
  10. Type “ls” to view the devices list. Scroll through the list an make sure synoboot2 is listed.
  11. Type “mkdir-p /mnt/synoboot” to make a directory to mount to.
  12. Type “mount synoboot2 /mnt/synoboot” to mount the boot files to the directory you just created.
  13. Type “cd /mnt/synoboot” to change into that directory.
  14. Type “ls” to list the files in the directory. Note that the names of the four files we put in the shared folder are listed, but these are the DSM Beta versions.
  15. Type “cp /volume1/test/checksum.syno /mnt/synoboot” to overwrite the beta file with the stable file from the “test” shared folder.
  16. Type “cp /volume1/test/grub_cksum.syno /mnt/synoboot” to overwrite the beta file with the stable file from the “test” shared folder.
  17. Type “cp /volume1/test/rd.gz /mnt/synoboot” to overwrite the beta file with the stable file from the “test” shared folder.
  18. Type “cp /volume1/test/zImage /mnt/synoboot” to overwrite the beta file with the stable file from the “test” shared folder.
  19. Go back into the DSM interface and shutdown the unit. Once the device is shut down, eject all disks. This step is important: if you do not eject all the disks, the next power up will detect an issue and recover the beta boot image.
  20. Power the device on and find it (use Synology Assistant to help with this). It should complain that the unit has no disks inserted. Put the disks back in now and wait for all drives to spin up (the HDD leds light up).
  21. Once all disks are in and powered/spun up, click on “connect again”. A couple screens later, you will be asked to reinstall DSM. Choose the manual install root and choose the DSM 15254.pat file so that the boot image is overwritten correctly.
  22. Once it all completes you’re good to go. Data on the array(s) will still be intact (shared folder data), you’ll just need the re-apply the configuration and packages.

 

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Author: PantsManUK

Twenty-plus years in IT and/or gaming in one form or another. My proudest moment was getting through Jet Pac on the Sinclair Spectrum 48K ;-)

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