atop vs Monit

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.

Monit is a free, open-source utility for managing and monitoring Unix systems, available for Linux, macOS, and self-hosted deployment. It watches local daemon processes and can restart a stopped process or stop one using too many resources. It checks files, directories, and filesystems for timestamp, checksum, or size changes, and tests TCP, UDP, and Unix domain sockets using protocols such as HTTP and SMTP. Scheduled program or script checks can trigger actions or alerts based on exit values. Monit tracks CPU, memory, system load, and network interfaces, and sends customizable error alerts to syslog or its own log. Its HTTP(S) interface displays service status and allows process control and monitoring changes. It works with init, upstart, and systemd, can use existing run-level scripts, and can run as PID 1 in containers. The maker says it uses statically linked OpenSSL 3.5.7 and dynamically linked PAM support.