开机显示如下信息：
Kernel panic - not syncing: VPS: Unable to mount root fs on unknown-block(8,1)
CPU:1 PID:1 Comm: swapper/0 Not tained 4.1.34-33-default #1
Hardware name: Dell Inc. Vostro 3546/036DYM, BIOS A09 11/03/2015
0000000000000086 0000000000000000 ffffffff8165f7d1 000000000000101e
ffffffff81a11f18 ffff8800c5a5500f ffffffff8165a5ca ffff88012ab8be60
ffffffff00000010 ffff88012ab8be48 ffff88012ab8bde8 ffff80012ab8be38C
Call Trace:
[<ffffffff810055ec>] dump_trace+0x8e/0x340
[<ffffffff8100597c>] show_stack_log_lvl+0xfe/0x1a0
[<ffffffff81006ec1>] show_stack+0x21/0x50
[<ffffffff8165f7di>] dump_stack+0x54/0x79
[<ffffffff8165a5ca>] panic+0xca/0x205
[<ffffffff81f2a5cd>] mount_block_root+0x29c/0x2ab
[<ffffffff81f2a75f>] prepare_namespace+0x133/0x169
[<ffffffff81f2a27d>] kernel_init_freeable+0x1ef/0x201
[<ffffffff816518ce>] kernel-init+0xe/0xf0
[<ffffffff816663e2>] ret_from_fork+0x42/0x70
Kernel Offset : disabled

Kernel Panic...重装吧

chroot 试试，然后重装内核，重新mkinitrd

已经找到办法了，谢了诸位。我以后再也不敢在更新过程中关机了。