Ubuntu apt-get无法安装php5.6

出现以下错误

Reading package lists... Done
Building dependency tree       
Reading state information... Done
Note, selecting 'php5.6-json' for regex 'php5.6'
Note, selecting 'php5.6-common' for regex 'php5.6'
0 upgraded, 0 newly installed, 0 to remove and 261 not upgraded.

使用第三方源

sudo apt-add-repository ppa:ondrej/php