atop vs nmon

atop is a free, GPL-licensed performance monitor for Linux. It uses a full-screen ASCII interface to report system and process activity at regular intervals. System-level views cover CPU, memory, swap, disk, and network activity. Process and thread views include CPU use, memory growth, disk use, and other statistics, including consumption by processes that finish during the interval. atop can save compressed raw counters for longer-term analysis, preserving daily logs for 28 days by default. The atopsar command turns those logs into system activity reports. It also reports CPU, memory, disk I/O utilization, and pressure for cgroup v2. An optional netatop kernel module adds per-process and per-thread TCP and UDP packet counts and bandwidth statistics. Displays can use bar graphs or detailed text, with columns adjusting to terminal width. Downloads list source and x86_64 RPM packages for version 2.13.0.

nmon is a free Linux tool for systems administration, tuning, and performance benchmarking. It collects system information and presents live readings in a terminal through a curses interface. Keyboard controls let operators turn individual data categories on or off. The display can include CPU, memory, network, disks, filesystems, NFS, top processes, and, in the Linux version, resources and processors. Captured readings can be written to a comma-separated file for later analysis or longer-term recording. nmonchart converts output into webpage graphs, while nmon Analyser loads files into Excel and creates graphs. njmon injectors can add JSON data to InfluxDB and Splunk, with real-time graphing through InfluxDB and Grafana. Binaries are listed for POWER, x86, x86_64, mainframe, and ARM Linux. Unsupported distributions require compiling with GCC and the ncurses development library. The Linux project is GPLv3; AIX nmon is integrated into topas and is not open source.