Ubuntu apt安装图形界面

Ubuntu用apt-get install ubuntu-desktop安装图形界面，文件下载好了，安装过程中突然停电。再次安装总是从上次安装的地方开始。想问下怎么重新下载安装，或是正确安装(我执行过apt-get clean命令)
以下是断电后再次安装时的信息:

Reading package lists...
Building dependency tree...
Reading state information...
ubuntu-desktop is already the newest version.
The following packages will be upgraded:
ubuntu-docs
1 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.
1 not fully installed or removed.
Need to get 0 B/1452 kB of archives.
After this operation, 37.0 MB of additional disk space will be used.
(Reading database ... 
dpkg: warning: files list file for package `ubuntu-docs' missing, assuming package has no files currently installed.
(Reading database ... 5%(Reading database ... 10%(Reading database ... 15%(Reading database ... 20%(Reading database ... 25%(Reading database ... 30%(Reading database ... 35%(Reading database ... 40%(Reading database ... 45%(Reading database ... 50%(Reading database ... 55%(Reading database ... 60%(Reading database ... 65%(Reading database ... 70%(Reading database ... 75%(Reading database ... 80%(Reading database ... 85%(Reading database ... 90%(Reading database ... 95%(Reading database ... 100%(Reading database ... 116252 files and directories currently installed.)
Preparing to replace ubuntu-docs 12.04.4 (using .../ubuntu-docs_12.04.4_all.deb) ...
Unpacking replacement ubuntu-docs ...
dpkg: error processing /var/cache/apt/archives/ubuntu-docs_12.04.4_all.deb (--unpack):
symbolic link '/usr/share/help/ast/ubuntu-help/a11y-locate-pointer.page' size has changed from 63 to 0
Errors were encountered while processing:
/var/cache/apt/archives/ubuntu-docs_12.04.4_all.deb