背景：

Linux系统(Ubuntu)在运行时，断电等非正常关机操作，会导致ext4文件系统数据损坏。严重时会导致系统崩溃。如下log就是系统数据损坏。检查方法：

1、开机log，如上log就是开机时，kernel监测到文件系统错误:

[    7.878756] EXT4-fs error (device mmcblk0p2): ext4_mb_generate_buddy:742: group 0, 14845 clusters in bitmap, 14822 in gd    [    8.484660] init: samba-ad-dc main process (995) terminated with status 1

[   14.248075] EXT4-fs error (device mmcblk0p2): ext4_mb_generate_buddy:742: group 1, 1 clusters in bitmap, 2 in gd

2、比如要检查的分区是/dev/mmcblk0p2，如下红色字体部分就是系统错误的信息。

~# tune2fs -l /dev/mmcblk0p2

tune2fs 1.42.9 (4-Feb-2014)

Filesystem volume name:

Last mounted on:          /

Filesystem UUID:          ab013911-6048-465f-8a1a-cf1420c7bb01

Filesystem magic number:  0xEF53

Filesystem revision #:    1 (dynamic)

Filesystem features:      ext_attr resize_inode dir_index filetype extent flex_bg sparse_super large_file huge_file uninit_bg dir_nlink extra_isize

Filesystem flags:         unsigned_directory_hash

Default mount options:    user_xattr acl

Filesystem state:         not clean with errors

Errors behavior:          Continue

Filesystem OS type:       Linux

Inode count:              393216

Block count:              1572864

Reserved block count:     78643

Free blocks:              289870

Free inodes:              169990

First block:              0

Block size:               4096

Fragment size:            4096

Reserved GDT blocks:      383

Blocks per group:         32768

Fragments per group:      32768

Inodes per group:         8192

Inode blocks per group:   512

Flex block group size:    16

Filesystem created:       Sat Sep 12 11:55:02 2015

Last mount time:          Mon Oct  5 00:56:20 2015

Last write time:          Mon Oct  5 00:56:32 2015

Mount count:              49

Maximum mount count:      -1

Last checked:             Sat Sep 12 11:55:02 2015

Check interval:           0 ()

Lifetime writes:          5936 MB

Reserved blocks uid:      0 (user root)

Reserved blocks gid:      0 (group root)

First inode:              11

Inode size:               256

Required extra isize:     28

Desired extra isize:      28

Default directory hash:   half_md4

Directory Hash Seed:      37b6421d-4697-4ff5-a68e-4a1e1ea81c0e

Journal backup:           inode blocks

FS Error count:           5

First error time:         Mon Oct  5 00:52:47 2015

First error function:     ext4_mb_generate_buddy

First error line #:       742

First error inode #:      0

First error block #:      0

Last error time:          Mon Oct  5 00:56:32 2015

Last error function:      ext4_mb_generate_buddy

Last error line #:        742

Last error inode #:       0

Last error block #:       0

修复方法：

1、手动修复：借助其他完整系统启动，对所在磁盘分区卸载，比如要修复/dev/mmcblk0p2,

执行命令 fsck.ext4 /dev/mmcblk0p2 可检查修复系统；

2、自动修复：

条件：

(1)、

自动修复要保证，bootloader参数bootargs 生命挂载以制度方式挂载根文件系统

console=tty1 console=ttySAC2,115200n8 root=UUID=e139ce78-9841-40fe-8823-96a304a09859 rootwait

ro

如果最后ro是rw，将不能完成自动修复。

(2)、

编辑/etc/fstab 挂载最后一个选项设置为1，标明启动时自动检测文件系统，如下：

UUID=e139ce78-9841-40fe-8823-96a304a09859       /       ext4    errors=remount-ro,noatime,nodiratime            01

(3)、

编辑 /etc/default/rcS 最后一个选项(其他linux系统有区别)

# automatically repair filesystems with inconsistencies during boot

FSCKFIX=yes

然后，可以参考/etc/init/mountall.conf    description     "Mount filesystems on boot"

start on startup

stop on starting rcS

expect daemon

task

emits virtual-filesystems

emits local-filesystems

emits remote-filesystems

emits all-swaps

emits filesystem

emits mounting

emits mounted

script

. /etc/default/rcS || true

[ -f /forcefsck ] && force_fsck="--force-fsck"

[ "$FSCKFIX" = "yes" ] && fsck_fix="--fsck-fix"

# Doesn't work so well if mountall is responsible for mounting /proc, heh.

if [ -e /proc/cmdline ]; then

read line < /proc/cmdline

for arg in $line; do

case $arg in

-q|--quiet|-v|--verbose|--debug)

debug_arg=$arg

;;

esac

done < /proc/cmdline

fi

# set $LANG so that messages appearing in plymouth are translated

if [ -r /etc/default/locale ]; then

. /etc/default/locale || true

export LANG LANGUAGE LC_MESSAGES LC_ALL

fi

exec mountall --daemon $force_fsck $fsck_fix $debug_arg

end script

post-stop script

rm -f /forcefsck 2>dev/null || true

end script

(4)、系统检测到分区有问题时，会再根目录下创建一个空文件/forcefsck，重启后，执行mountall，自动进行修复，然后删除forcefsck，也可以手动创建/forcefsck，系统同样会在下次启动时强制检查修复文件系统；

Log：

系统启动检查修复过程的log，不在/var/log/fsck/目录下，而是在/var/log/upstart/目录下，文件为 mountall.log，如下：# cat mountall.log

mount: mount point /media/boot does not exist

mountall: mount /media/boot [382] terminated with status 32

mountall: Filesystem could not be mounted: /media/boot

Skipping /media/boot at user request

Skipping /media/boot at user request

Skipping /media/boot at user request

fsck from util-linux 2.20.1

e2fsck 1.42.9 (4-Feb-2014)

/dev/mmcblk0p2: clean, 223220/393216 files, 1282976/1572864 blocks

其他：

也可以通过设置 系统挂载的次数来自动检查修复文件系统

比如：

tune2fs -c 30 /dev/mmcblk0p2 系统每启动30次，就会检查修复一次。

修复完成后，通过 tune2fs -l /dev/mmcblk0p2看到没有错误信息。