command, it creates a phd2 directory and a build sub-directory under it, with what appears to be the files your (make -j $(expr $(nproc) + 2) needs. I cd'd over to that to issue the command below:
The command make -j $(expr $(nproc) + 2) yields the following error: make: *** No targets specified and no makefile found. Stop.
I think the expr and nproc variable is not defined. What goes in there?
Where ever you like. Git clone will download the source code into a folder. You then create a build directory within it and cd into it. Then run the make command.
You cannot run make directly, cmake is required first.
Also cmake as some interesting option, for example if using all INDI driver you can specify -DOPENSOURCE_ONLY=1
This prevent PHD2 to install its own libasi and libqhy, this keep your system cleaner by not having multiple version of this libraries installed.