升级到 15.04 后，我在了解 systemd 时获得了很多乐趣。我想我一切正常，除了无法停止 mysql.service；systemctl 命令只是挂起，而 mysql 只是继续运行。有没有其他人经历过这个或可能知道发生了什么？
我升级 MySQL 服务器失败。这是我尝试过的：
我首先发出这个命令来更新包列表：
sudo apt-get update
然后，通过以下方式升级：
sudo apt-get upgrade
它显示以下错误：
Reading package lists... Done
Building dependency tree
Reading state information... Done
You might want to run 'apt-get -f install' to correct these.
The following packages have unmet dependencies:
mysql-server-5.5 : Depends: mysql-server-core-5.5 (= 5.5.28-0ubuntu0.12.04.2) but 5.5.31-0ubuntu0.12.04.1 is installed
E: Unmet dependencies. Try using -f.
显然安装了更新的版本（但为什么？我没有手动安装）。好的，正如它所暗示的，我发出命令来尝试修复：
sudo apt-get -f install
这是输出：
Reading package lists... Done
Building dependency tree
Reading state information... Done
Correcting dependencies... Done
The following extra packages …升级到 12.04 后 mysql 服务器无法启动。
我尝试了很多不同的东西，但没有任何运气。
现在，当我尝试安装它时，我得到：
$ sudo apt-get install mysql-server-5.5
Reading package lists... Done
Building dependency tree
Reading state information... Done
Suggested packages:
tinyca
The following NEW packages will be installed:
mysql-server-5.5
0 upgraded, 1 newly installed, 0 to remove and 39 not upgraded.
Need to get 0 B/8,708 kB of archives.
After this operation, 31.3 MB of additional disk space will be used.
Preconfiguring packages ...
Selecting previously unselected package mysql-server-5.5.
(Reading database ... 243325 files and …