解决还原centos后 根目录空间不足的情况

环境：kvm
系统：CentOS7
故障描述：10g的ssd，可使用大小仅有2g
解决过程：

    某次重装系统后，安装软件总提示磁盘空间不足，检查之下发现仅有2G空间，实则明明是10G的ssd，以下为排错过程：

1、df -h查看vda1大小为2.7G

#df -h
Filesystem Size Used Avail Use% Mounted on
/dev/vda1 2.7G 2.4G 236M 91% /
devtmpfs 234M 0 234M 0% /dev
tmpfs 244M 0 244M 0% /dev/shm
tmpfs 244M 4.5M 240M 2% /run
tmpfs 244M 0 244M 0% /sys/fs/cgroup
tmpfs 49M 0 49M 0% /run/user/0

2、fdisk查看vda1一共9959232个block，大小应为9959232KB=9.725.8GB

#fdisk -l
Disk /dev/vda: 10.7 GB, 10737418240 bytes, 20971520 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk label type: dos
Disk identifier: 0x000f3770
   Device Boot      Start         End      Blocks   Id  System
/dev/vda1   *        2048    19920511     9959232   83  Linux
/dev/vda2        19920512    20969087      524288   82  Linux swap / Solaris

3、尝试能否通过新建分区解决的时候，发现了另一个bug，居然能看到主机的真实磁盘大小！

#fdisk /dev/vda
Welcome to fdisk (util-linux 2.23.2).

Changes will remain in memory only, until you decide to write them.
Be careful before using the write command.

Command (m for help): u
Changing display/entry units to cylinders (DEPRECATED!).

Command (m for help): n
Partition type:
p primary (2 primary, 0 extended, 2 free)
e extended
Select (default p): p
Partition number (3,4, default 3): 3
First cylinder (1306-20805, default 1306): 
Using default value 1306
Last cylinder, +cylinders or +size{K,M,G} (1306-20805, default 20805): 
Using default value 20805
Partition 3 of type Linux and of size 149.4 GiB is set                                   

//剩余149.4G，加上我自己的10G,这块SSD的大小应该是160G的，当然仅此而已了，想要盗用还是不可能的，至少我办不到。囧

Command (m for help): q

fdisk -l                                                                                                   

//虽然fdisk看到的vda3貌似很厉害的样子

Disk /dev/vda: 10.7 GB, 10737418240 bytes, 20971520 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk label type: dos
Disk identifier: 0x000f3770

Device Boot Start End Blocks Id System
/dev/vda1 * 2048 19920511 9959232 83 Linux
/dev/vda2 19920512 20969087 524288 82 Linux swap / Solaris
/dev/vda3 20969088 334232324 156631618+ 83 Linux

4、partprobe的时候果然报错了哈哈哈

#partprobe 
Error: Can't have a partition outside the disk!

5、fdisk看到的vda1大小正常，并且也没有多余的可用空间来新建分区，说明问题不是出在磁盘空间分配上，此路不通。

所以删除那个奇葩的vda3，尝试resize方法

#resize2fs /dev/vda1 （其实核心就是这个命令）
 resize2fs 1.42.9 (28-Dec-2013) Filesystem at /dev/vda1 is mounted on /; on-line resizing required old_desc_blocks = 1, new_desc_blocks = 2 The filesystem on /dev/vda1 is now 2489808 blocks long.

6、fdisk数据并无变化，但df显示磁盘空间终于正常了，安装程序也不会再提示磁盘空间不足，故障排除。

fdisk -l

Disk /dev/vda: 10.7 GB, 10737418240 bytes, 20971520 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk label type: dos
Disk identifier: 0x000f3770

Device Boot Start End Blocks Id System
/dev/vda1 * 2048 19920511 9959232 83 Linux
/dev/vda2 19920512 20969087 524288 82 Linux swap / Solaris

# df -h
Filesystem Size Used Avail Use% Mounted on
/dev/vda1 9.3G 2.4G 6.6G 27% /
devtmpfs 234M 0 234M 0% /dev
tmpfs 244M 0 244M 0% /dev/shm
tmpfs 244M 4.5M 240M 2% /run
tmpfs 244M 0 244M 0% /sys/fs/cgroup
tmpfs 49M 0 49M 0% /run/user/0