Search code examples
google-compute-enginesystemdisk

google compute engine -- mount old system disk on new disk built from snapshot?

I have a GCE ubuntu 18.04 system that overflowed the / partition. Consequently, I can't start a remote shell to fix it. I created a new system from a snapshot, and stopped the old system.

I want to attach the old system disk to the new system, mount it, and delete a bunch of stuff so I can restart it.

However, when I edit the new system disk in the cloud console, the old system disk does not show up as a possible disk to attach. What do I need to do to the old system disk to both preserve it as a system disk, and allow attaching it to the new system?

Solution

  • What do I need to do to the old system disk to both preserve it as a system disk, and allow attaching it to the new system?

    Either the disk is still attached or the new instance is located in a different zone. Follow the steps below.

    STEP 1:

    Shut down your instance with the disk space problem. Login into the Google Cloud Console. Go to Compute Engine -> VM instances. Click on your instance and make note of the “Boot disk” name. This will be the first disk under “Boot disk and local disks”.

    STEP 2:

    Create a snapshot of the boot disk before doing anything further. While still in Compute Engine -> Disk. Click on your boot disk. Click on “CREATE SNAPSHOT”.

    STEP 3:

    Create a new instance in the same zone. A micro instance will work.

    STEP 4:

    Open a Cloud Shell prompt (this also works from your desktop if gcloud is set up). Execute this command. Replace NAME with your instance name (broken system) and DISK with the boot disk name and ZONE with the zone that the system is in:

    gcloud compute instances detach-disk NAME --disk=DISK --zone=ZONE

    Make sure that the command did not report an error.

    STEP 5:

    Now we will attach this disk to the new instance that you created.

    Make sure that the repair instance is running before attaching the second disk. Sometimes an instance can get confused on which disk to boot from if more than one disk is bootable.

    Go to Compute Engine -> VM instances. Click on your instance. Click Edit. Under “Additional disks” click “Add item”. For name enter/select the disk that you detached from your broken instance. Click Save.

    STEP 6:

    SSH into your new instance with both disks attached.

    STEP 7:

    Mount the second disk to the root file system.

    • Become superuser. Execute sudo -s
    • Execute df. Make sure that /dev/sdb1 is not mounted.
    • Create a directory for the mount point: mkdir /mnt/repair
    • Mount the second disk: mount /dev/sdb1 /mnt/repair