我正在尝试在ubunto 17.10上安装php7.2-gd，但是遇到一些依赖问题。
sudo apt-get install php7.2-gd
Reading package lists... Done
Building dependency tree
Reading state information... Done
Some packages could not be installed. This may mean that you have requested an impossible situation or if you are using the unstable distribution that some required packages have not yet been created or been moved out of Incoming.
The following information may help to resolve the situation:
The following packages have unmet dependencies:
php7.2-gd : Depends: libjpeg62-turbo (>= 1.3.1) but it is not installable
E: Unable to correct problems, you have held broken packages.
我尝试安装libjpeg62-turbo，但是得到了以下信息：
sudo apt-get install libjpeg62-turbo
Reading package lists... Done
Building dependency tree
Reading state information... Done
Package libjpeg62-turbo is not available but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source
E: Package 'libjpeg62-turbo' has no installation candidate