atop is a useful tool that displays system load information alongside process information in a similar style to top.
As in the screenshot below illustrates, the top window shows system-level information and the bottom one process information.
|Atop in Action|
The lines in the top window show:
- PRC: Total CPU time in system and user mode, total number of processes and of zombie processes, and the number of processes that exited during the polling interval. The default polling interval is 10 seconds. Use 'i' to change it interactively or 'z' to pause it.
- CPU and CPL: CPU utilization and load (averaged over 1, 5 and 15 minutes).
- MEM and SWP: Amount of memory and swap space that is available and where it's allocated. vmcom and vmlim show how much virtual memory space is committed and what the limit is.
- DSK: disk utilization. avio shows the average number of milliseconds per request.
- NET: Network utilization for the TCP layer ("transport"), the IP layer ("network") and each interface.
All of these use color to indicate if there are any problems.
The bottom window shows active processes (use 'a' to toggle showing all processes). 'g' shows the default process information, or use 'm' to show memory information. VGROW and RGROW on the memory information screen show the increase in virtual and memory usage during the polling interval; check the man page for further information about other columns. Note that you can also kill a process from here by hitting 'k'.
There are various other top-alike programs out there for other resources. Try iftop, for example, to take a look at your network interface statistics! Or htop to get top information in colour and with scrolling.