There are many alternatives to nmon for Linux if you are looking for a replacement. The best Linux alternative is htop, which is both free and Open Source. If that doesn't suit you, our users have ranked more than 10 alternatives to nmon and nine of them are available for Linux so hopefully you can find a suitable replacement. Other interesting Linux alternatives to nmon are Glances (Free, Open Source), GNOME System Monitor (Free, Open Source), vtop (Free, Open Source) and psutil (Free, Open Source).
Glances is a cross-platform monitoring tool which aims to present a large amount of monitoring information through a curses or Web based interface. The information dynamically adapts depending on the size of the user interface.
psutil is a module providing an interface for retrieving information on all running processes and system utilization (CPU, memory, disks, network, users) in a portable way by using Python, implementing many functionalities offered by command line tools such as: ps, top, df...
libstatgrab is a library that provides cross platform access to statistics about the system on which it's run. It's written in C and presents a selection of useful interfaces which can be used to access key system statistics.