異常關閉linux電源容易導致啓動失敗進入emergency mode。
進入emergency mode的原因很多，通常是磁盤關機出現問題，可以通過用linux引導盤到rescue模式下查看原因並修復。
如果是lvm卷出現問題，可以用如下方式嘗試修復：
1， lvm vgscan查看有哪些vg
# lvm vgscan
Reading volume groups from cache.
Found volume group "centos_master" using metadata type lvm2
2， 激活vg
# lvm vgchange -ay
2 logical volume(s) in volume group "centos_master" now active
3， 查看邏輯卷
# lvm lvdisplay
--- Logical volume ---
LV Path /dev/centos_master/swap
LV Name swap
VG Name centos_master
LV UUID XAhwdw-yLyi-JDXx-NwGF-QDJv-c06h-Jm7iYD
LV Write Access read/write
LV Creation host, time master, 2018-12-05 23:49:56 +0800
LV Status available
# open 2
LV Size 2.00 GiB
Current LE 512
Segments 1
Allocation inherit
Read ahead sectors auto
- currently set to 8192
Block device 253:1
--- Logical volume ---
LV Path /dev/centos_master/root
LV Name root
VG Name centos_master
LV UUID ozZUmD-fyQE-TakK-MQgH-6Dvt-4Tdj-783S70
LV Write Access read/write
LV Creation host, time master, 2018-12-05 23:49:57 +0800
LV Status available
# open 1
LV Size <17.00 GiB
Current LE 4351
Segments 1
Allocation inherit
Read ahead sectors auto
- currently set to 8192
Block device 253:0
4，查看時哪個 lv掛載有問題，比如 mkdir /root/disk; mount /dev/centos_master/root /root/disk。 如果失敗則mount會報錯。
5，嘗試修復有問題的邏輯卷
# fsck /dev/centos_master/root
fsck，來自 util-linux 2.23.2
If you wish to check the consistency of an XFS filesystem or
repair a damaged filesystem, see xfs_repair(8).
6， 按照嚮導用xfs_repair進行修復。通常是metatdata與卷journallog不一致，可以用如下方式嘗試修復。
# xfs_repair -L /dev/centos_master/root