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filesystemsgoogle-compute-enginebootdisk

Google Compute Engine VM instance: VFS: Unable to mount root fs on unknown-block

My instance on Google Compute Engine is not booting up due to having some boot order issues.

So, I have created a another instance and re-configured my machine.

My questions:

  1. How can I handle these issues when I host some websites?
  2. How can I recover my data from old disk?

logs

  

    [    0.348577] Key type trusted registered
    [    0.349232] Key type encrypted registered
    [    0.349769] AppArmor: AppArmor sha1 policy hashing enabled
    [    0.350351] ima: No TPM chip found, activating TPM-bypass!
    [    0.351070] evm: HMAC attrs: 0x1
    [    0.351549]   Magic number: 11:333:138
    [    0.352077] block ram3: hash matches
    [    0.352550] rtc_cmos 00:00: setting system clock to 2015-12-19 17:06:53 UTC (1450544813)
    [    0.353492] BIOS EDD facility v0.16 2004-Jun-25, 0 devices found
    [    0.354108] EDD information not available.
    [    0.536267] input: AT Translated Set 2 keyboard as /devices/platform/i8042/serio0/input/input2
    [    0.537862] md: Waiting for all devices to be available before autodetect
    [    0.538979] md: If you don't use raid, use raid=noautodetect
    [    0.539969] md: Autodetecting RAID arrays.
    [    0.540699] md: Scanned 0 and added 0 devices.
    [    0.541565] md: autorun ...
    [    0.542093] md: ... autorun DONE.
    [    0.542723] VFS: Cannot open root device "sda1" or unknown-block(0,0): error -6
    [    0.543731] Please append a correct "root=" boot option; here are the available partitions:
    [    0.545011] Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(0,0)
    [    0.546199] CPU: 0 PID: 1 Comm: swapper/0 Not tainted 3.19.0-39-generic #44~14.04.1-Ubuntu
    [    0.547579] Hardware name: Google Google, BIOS Google 01/01/2011
    [    0.548728]  ffffea00008ae140 ffff880024ee7db8 ffffffff817af92b 000000000000111e
    [    0.549004]  ffffffff81a7c7c8 ffff880024ee7e38 ffffffff817a976b ffff880024ee7dd8
    [    0.549004]  ffffffff00000010 ffff880024ee7e48 ffff880024ee7de8 ffff880024ee7e38
    [    0.549004] Call Trace:
    [    0.549004]  [] dump_stack+0x45/0x57
    [    0.549004]  [] panic+0xc1/0x1f5
    [    0.549004]  [] mount_block_root+0x210/0x2a9
    [    0.549004]  [] mount_root+0x54/0x58
    [    0.549004]  [] prepare_namespace+0x16d/0x1a6
    [    0.549004]  [] kernel_init_freeable+0x1f6/0x20b
    [    0.549004]  [] ? initcall_blacklist+0xc0/0xc0
    [    0.549004]  [] ? rest_init+0x80/0x80
    [    0.549004]  [] kernel_init+0xe/0xf0
    [    0.549004]  [] ret_from_fork+0x58/0x90
    [    0.549004]  [] ? rest_init+0x80/0x80
    [    0.549004] Kernel Offset: 0x0 from 0xffffffff81000000 (relocation range: 0xffffffff80000000-0xffffffffbfffffff)
    [    0.549004] ---[ end Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(0,0)
Solution
    1. How to handle these issues when I host some websites?

    I'm not sure how you got into this situation, but it would be nice to have additional information (see my comment above) to be able to understand what triggered this issue.

    1. How to recover my data from old disk?

    Attach and mount the disk

    Assuming you did not delete the original disk when you deleted the instance, you can simply mount this disk from another VM to read the data from it. To do this:

    1. attach the disk to another VM instance, e.g.,

      gcloud compute instances attach-disk $INSTANCE --disk $DISK

    2. mount the disk:

      sudo mkdir -p /mnt/disks/[MNT_DIR]

      sudo mount [OPTIONS] /dev/disk/by-id/google-[DISK_NAME] /mnt/disks/[MNT_DIR]

      Note: you'll need to substitute appropriate values for:

      • MNT_DIR: directory
      • OPTIONS: options appropriate for your disk and filesystem
      • DISK_NAME: the id of the disk after you attach it to the VM

    Unmounting and detaching the disk

    When you are done using the disk, reverse the steps:

    Note: Before you detach a non-root disk, unmount the disk first. Detaching a mounted disk might result in incomplete I/O operation and data corruption.

    1. unmount the disk

      sudo umount /dev/disk/by-id/google-[DISK_NAME]

    2. detach the disk from the VM:

      gcloud compute instances detach-disk $INSTANCE --device-name my-new-device