I have installed ZM 1.30.4 on a DebianDog OS. Entire OS and a running ZM with 1 local camera and 1 network camera in 265 megs of RAM. It is a frugal install with a save folder saving all events to a internal HDD.
Another minimal OS, XenialDog is set up in a similar fashion. ZoneMinder is very easy to install in both operating systems since both use apt,apt-get and the synaptic package manager and it is possible to directly copy and paste the commands from :
https://wiki.zoneminder.com/Ubuntu_Serv ... e_easy_way
or
https://wiki.zoneminder.com/Debian_9_64 ... e_Easy_Way
both OS's with ZM run in 265-310 megs of RAM