修復錯誤配置fstab文件導致系統無法正常啓動
1. 問題再現
1.1. 操作環境說明
操作系統：CentOS5.2
硬盤分區情況：
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[root@localhost ~]# fdisk /dev/sda
The number of cylinders for this disk is set to 1305.
There is nothing wrong with that, but this is larger than 1024,
and could in certain setups cause problems with:
1) software that runs at boot time (e.g., old versions of LILO)
2) booting and partitioning software from other OSs
(e.g., DOS FDISK, OS/2 FDISK)
Command (m for help): p
Disk /dev/sda: 10.7 GB, 10737418240 bytes
255 heads, 63 sectors/track, 1305 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Device Boot Start End Blocks Id System
/dev/sda1 * 1 522 4192933+ 83 Linux
/dev/sda2 523 783 2096482+ 83 Linux
/dev/sda3 784 914 1052257+ 82 Linux swap / Solaris
Command (m for help): v
6288172 unallocated sectors |
fstab文件：
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[root@localhost ~]# more /etc/fstab
LABEL=/ / ext3 defaults 1 1
LABEL=/tmp /tmp ext3 defaults 1 2
tmpfs /dev/shm tmpfs defaults 0 0
devpts /dev/pts devpts gid=5,mode=620 0 0
sysfs /sys sysfs defaults 0 0
proc /proc proc defaults 0 0
LABEL=SWAP-sda3 swap swap defaults 0 0 |
1.2. 創建新的分區，並配置fstab文件
1.2.1. 創建分區
在/dev/sda上創建新的主分區sda4
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[root@localhost ~]# fdisk /dev/sda
The number of cylinders for this disk is set to 1305.
There is nothing wrong with that, but this is larger than 1024,
and could in certain setups cause problems with:
1) software that runs at boot time (e.g., old versions of LILO)
2) booting and partitioning software from other OSs
(e.g., DOS FDISK, OS/2 FDISK)
Command (m for help): p
Disk /dev/sda: 10.7 GB, 10737418240 bytes
255 heads, 63 sectors/track, 1305 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Device Boot Start End Blocks Id System
/dev/sda1 * 1 522 4192933+ 83 Linux
/dev/sda2 523 783 2096482+ 83 Linux
/dev/sda3 784 914 1052257+ 82 Linux swap / Solaris
Command (m for help): n
Command action
e extended
p primary partition (1-4)
p
Selected partition 4
First cylinder (915-1305, default 915):
Using default value 915
Last cylinder or +size or +sizeM or +sizeK (915-1305, default 1305):
Using default value 1305
Command (m for help): p
Disk /dev/sda: 10.7 GB, 10737418240 bytes
255 heads, 63 sectors/track, 1305 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Device Boot Start End Blocks Id System
/dev/sda1 * 1 522 4192933+ 83 Linux
/dev/sda2 523 783 2096482+ 83 Linux
/dev/sda3 784 914 1052257+ 82 Linux swap / Solaris
/dev/sda4 915 1305 3140707+ 83 Linux
Command (m for help): w
The partition table has been altered!
Calling ioctl() to re-read partition table.
WARNING: Re-reading the partition table failed with error 16: Device or resource busy.
The kernel still uses the old table.
The new table will be used at the next reboot.
Syncing disks. |
創建文件系統，將Label設置爲other
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[root@localhost ~]# mke2fs -j -L other /dev/sda4
mke2fs 1.39 (29-May-2006)
Filesystem label=other
OS type: Linux
Block size=4096 (log=2)
Fragment size=4096 (log=2)
393216 inodes, 785176 blocks
39258 blocks (5.00%) reserved for the super user
First data block=0
Maximum filesystem blocks=805306368
24 block groups
32768 blocks per group, 32768 fragments per group
16384 inodes per group
Superblock backups stored on blocks:
32768, 98304, 163840, 229376, 294912
Writing inode tables: done
Creating journal (16384 blocks): done
Writing superblocks and filesystem accounting information: done
This filesystem will be automatically checked every 20 mounts or
180 days, whichever comes first. Use tune2fs -c or -i to override.
[root@localhost ~]# e2label /dev/sda4
other |
Mount /dev/sda4到 /others
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[root@localhost /]# mkdir /others
[root@localhost /]# mount /dev/sda4 /others
[root@localhost /]# mount
/dev/sda1 on / type ext3 (rw)
proc on /proc type proc (rw)
sysfs on /sys type sysfs (rw)
devpts on /dev/pts type devpts (rw,gid=5,mode=620)
/dev/sda2 on /tmp type ext3 (rw)
tmpfs on /dev/shm type tmpfs (rw)
none on /proc/sys/fs/binfmt_misc type binfmt_misc (rw)
sunrpc on /var/lib/nfs/rpc_pipefs type rpc_pipefs (rw)
/dev/sda4 on /others type ext3 (rw)
[root@localhost /]# cd /others
[root@localhost others]# ls -l
total 16
drwx------ 2 root root 16384 Nov 21 19:35 lost+found
[root@localhost others]# |
修改fstab文件
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[root@localhost /]# vi /etc/fstab
LABEL=/ / ext3 defaults 1 1
LABEL=/tmp /tmp ext3 defaults 1 2
tmpfs /dev/shm tmpfs defaults 0 0
devpts /dev/pts devpts gid=5,mode=620 0 0
sysfs /sys sysfs defaults 0 0
proc /proc proc defaults 0 0
LABEL=SWAP-sda3 swap swap defaults 0 0
LABEL=/other /others ext3 defaults 1 2 |
請注意：這裏用到是LABEL而不是設備名（/dev/sda4），但是這裏把卷標寫錯，應該是other，前面沒有 /。
並且沒有運行mount -a命令來驗證配置是否正確。
接着就直接重啓系統了（init 6）。
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[root@localhost /]# init 6 |
1.3. 問題的出現
1.3.1. 在重啓時遇到問題
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圖1.1 |
系統發現fstab中的LABEL=/other卷標不存在。
2. 故障的解決過程
2.1. 進入運行級別1
輸入root用戶密碼，進入運行級別1
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圖2.1 |
此時試圖修改/etc/fstab文件
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圖2.2 |
此時發現文件系統是隻讀的
重新mount /
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圖2.3 |
再次修改fstab文件
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圖2.4 |
修改完成，重啓系統（init 6）。
系統可以正常啓動，問題解決了。
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圖2.5 |
3. 問題總結
以上問題的出現是由於錯誤配置了/etc/fstab文件，在系統重啓時，無法識別卷標（/other），從而導致無法正常啓動。如果在修改/etc/fstab文件後，運行mount -a命令驗證一下配置是否正確，則可以避免此類問題。
問題的修復方法不僅適用於以上所描述的問題，同樣可以處理由於錯誤修改配置導致系統無法啓動的其他問題。
問題的解決過程中，重新mount /是比較關鍵的一步（mount -n -o remount,rw /）。如果沒有此步操作，則文件系統處於只讀狀態，導致不能修改配置文件並保存，修復存在的問題。