How to install missing init system helpers

The init-system-helpers package that provides a helper tools for all init systems is not available in primary Debian Wheezy repositories. You need to use wheezy-backports repository to install it on that operating system.

Add wheezy-backports repository.

$ cat <<EOF | sudo tee /etc/apt/sources.list.d/wheezy-backports.list
deb http://http.debian.net/debian wheezy-backports main
EOF

Update package index.

$ sudo apt-get update

Install init-system-helpers package.

$ sudo apt-get install init-system-helpers

You do not need to explicitly specify wheezy-backports as target release, because this package is not available in primary Debian Wheezy repositories.