List processes in real-time

Like the ps command, the top command is used to list processes currently running on your system. But top has one advantage over ps – it updates its display every couple of seconds, so you can see how the resource usage changes in almost real-time.

Consider the following top output (to invoke the command, simply type top in the terminal):

As you can see from the picture above, the top command displays a variety of useful information about processes. Here is a brief description of the most important ones:

• PID – the process ID of the process.
• USER – the owner of the process.
• PR – the priority of the process.
• NI – the nice value of the process.
• VIRT – the total amount of virtual memory used by the process.
• RES – the non-swapped physical memory the process has used.
• %CPU – the processor’s share of the CPU time.
• %MEM – the processor’s share of the physical memory.
• COMMAND – the command used to start the process.

By default, top sorts its entries by CPU usage, but you can sort the entries by other columns as well:

• to sort by memory usage, press M.
• to reverse sort the output, press R.
• to sort by the CPU usage, press P.
• to sort by other fields, use the < and > keys.

Kill processes with top

You can also kill processes while in the top window. For example, if you notice that a running process is using too much CPU time, you can kill it by pressing k and specifying the PID.