How do I install a man page file system-wide?
For example, if I have a man page file examplecommand.1, how do I install it so that I can just type man examplecommand to view it?
First, find out which section your man page belongs to. If its a command, it probably belongs to section 1. You can read the manpage for the man command 
to see a description of the different sections and their corresponding numbers.
Copy your man page to /usr/local/share/man/man1/ (change 1 to your section number if need be). You can also install it to /usr/share/man/man1/, but it's best practice to use the /usr/local/ directory for files that are installed without using the APT package manager. You can also optionally symlink over the file instead of copying it if you want:
# First, ensure your local man page directory exists for your section of
# interest (section 1 in this case, so the `man1` dir)
sudo mkdir -p /usr/local/share/man/man1
# Option 1: **copy** over the man page to section 1
sudo cp examplecommand.1 /usr/local/share/man/man1/
# Option 2: **symlink** over the man page to section 1.
# NB: This cmd assumes you are already cd'ed into the dir in
# which "examplecommand.1" is found, prior to running this cmd.
sudo ln -si "$PWD/examplecommand.1" /usr/local/share/man/man1/
Run the mandb command. This will update man's internal database:
sudo mandb
That's it! You should be able to view the man page by running:
man 1 examplecommand
man command mandb command /usr/bin/dh_installman if you can read Perl, installed with the debhelper package.
