Installing Crashplan 7.0 on a supported Linux system is relatively simple. Just follow the instructions on https://support.code42.com/Administrator/Small_Business/Get_started_with_CrashPlan_for_Small_Business/Download_and_install_CrashPlan_for_Small_Business
Essentially just login to your dashboard from there, then:
> tar xvf CrashPlanSmb_7.0.<something>_Linux.tgz
> cd crashplan-install/
> sudo ./install.sh
and follow the instructions.
Logs are located in /usr/local/crashplan/log by default
Since there is no monitor, the CrashPlanDesktop command will not work, and you can't configure the backup system.
There are some, somewhat complicated, ways to get a CrashPlan client on another machine to talk to the engine on the server.
I found it simpler to install X11 on the server and XQuartz (https://www.xquartz.org/) on my Mac client. On a Windows client, Xming (http://www.straightrunning.com/XmingNotes/) should work.
Install XQuartz on your client, log out and in again to get the $DISPLAY variable set in terminals.
Open a terminal, ssh to your server. Install X11 and libraries needed by Crashplan.
> sudo apt-get install xorg libasound2
End ssh session and connect again with the -X option. XQuartz may start on it's own if not running.
> ssh -X <server>
Welcome to Ubuntu 18.04.2 LTS (GNU/Linux 4.15.0-54-generic x86_64)
...
/usr/bin/xauth: file /home/user/.Xauthority does not exist
> CrashPlanDesktop
Wait a few seconds for the Crashplan UI to show up on your Mac. Configure as normal.
If it does not show up after a while, you may need some more libraries. By default, the UI error log is in ~/.code42/log/ui_errors.log.
Missing libraries show up something like this:
/usr/local/crashplan/electron/crashplan: error while loading shared libraries: libasound.so.2: cannot open shared object file: No such file or directory
Search the web for error while loading shared libraries: <something>: and you'll hopefully find what package to install.
If $DISPLAY somehow is missing something like this shows up:
(crashplan:11647): Gtk-WARNING **: 12:27:55.223: cannot open display:
First try to end the ssh session, and log out of your Mac. Maybe even reboot if you feel like it. Log into the Mac again and start from ssh -X above. If still nothing start googling in despair.
If you don't plan on administering Crashplan on the server and don't need X11 and the libraries installed, remove the packages you installed.
sudo apt-get purge xorg libasound2
sudo apt-get autoremove