Fix an ECS instance that repeatedly goes down at startup with a "VFS: Unable to mount root fs on unknown-block" kernel panic by replacing the system disk or rolling back from a snapshot.
Symptom
An ECS instance repeatedly goes down during startup and displays a call stack similar to the following:
[ 1.573197] Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(0,0)
[ 1.574179] CPU: 4 PID: 1 Comm: swapper/0 Not tainted 3.10.0-1160.6.1.el7.x86_64 #1
[ 1.575045] Hardware name: Alibaba Cloud Alibaba Cloud ECS, BIOS 8f19b21 04/01/2014
[ 1.575900] Call Trace:
[ 1.576246] [<ffffffff8f381400>] dump_stack+0x19/0x1b
[ 1.576845] [<ffffffff8f37a958>] panic+0xe8/0x21f
[ 1.577433] [<ffffffff8f98b794>] mount_block_root+0x291/0x2a0
[ 1.578122] [<ffffffff8f98b7f6>] mount_root+0x53/0x56
[ 1.578719] [<ffffffff8f98b935>] prepare_namespace+0x13c/0x174
[ 1.579425] [<ffffffff8f98b412>] kernel_init_freeable+0x222/0x249
[ 1.580150] [<ffffffff8f98ab28>] ? initcall_blacklist+0xb0/0xb0
[ 1.580838] [<ffffffff8f36fa90>] ? rest_init+0x80/0x80
[ 1.581462] [<ffffffff8f36fa9e>] kernel_init+0xe/0x100
[ 1.582073] [<ffffffff8f394df7>] ret_from_fork_nospec_begin+0x21/0x21
[ 1.582814] [<ffffffff8f36fa90>] ? rest_init+0x80/0x80Cause
The instance cannot find the root partition file system. A failed or interrupted kernel update may have damaged rootfs.
Solution
Before you perform the operations in the solution on a instance on which the issue occurred, we recommend that you create snapshots for the instance to back up data. This prevents data loss caused by accidental operations. For information about how to create a snapshot, see Create snapshot manually.
Replace the operating system of an instance or roll back a disk by using a snapshot.