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I use Ubuntu 16.04. APT cannot seem to find the package
root@kevin:/# sudo apt install m4 Reading package lists... Done Building dependency tree Reading state information... Done Package m4 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 'm4' has no installation candidate
sudo apt-get upgrade && apt-get update
This didn't make any difference.
root@kevin:/# grep main /etc/apt/sources.list # deb cdrom:[Ubuntu 16.04.3 LTS _Xenial Xerus_ - Release amd64 (20170801)]/ xenial main restricted # deb-src http://cn.archive.ubuntu.com/ubuntu/ xenial main restricted # deb-src http://cn.archive.ubuntu.com/ubuntu/ xenial-updates main restricted ## extensively as that contained in the main release, although it includes # deb-src http://cn.archive.ubuntu.com/ubuntu/ xenial-backports main restricted universe multiverse # deb-src http://security.ubuntu.com/ubuntu xenial-security main restricted