Atop is an open source project that provides users with a sophisticated and interactive process viewer, system monitoring and task manager software that runs entirely from the Linux console or any X11 terminal emulator application.
Key features include highlight of critical resources, ability to view only activities or deviations, permanent logging of resource utilization, scalable window width, accumulated process activity per user or program, view network activity per process.
In addition, it uses all relevant resources of a Linux system, including CPU, RAM and SWAP, as well as network utilization and disk I/O, displays resource utilization by all processes that were active at a certain moment.
The application has been designed from the ground up as a drop-in replacement for the old-school Top process viewer program found in almost all Linux-based operating systems, as well as various under Unices like BSD or Solaris.
Its Ncurses-bases ASCII user interface comprises two main view areas of almost the same size and look, as opposed to the ones of traditional top programs, such as Unix Top or Htop. Both areas are updated on a regular basis, in real time.
On the upper part it displays detailed information about system-level activity regarding the current utilization of CPU, system memory, Swap partition, disks and network interfaces. This is the system monitoring part of the application.
On the second part, the application displays the current running processes that uses the CPU (Central Processing Unit) of the machine. It sorts them by PID, Real User ID (RUID) and Effective User ID (EUID), threads, system or user CPU utilization, virtual and resident memory growth, disk reading and writing state, exit code, and command.
All in all, Atop is a decent process viewer and task management application that displays only the active system-resources and processes. However, we prefer to use the Htop or Top programs for our daily system monitoring tasks.