Linux: Monitor Processes: top

Linux top is a command line program that lets you monitor CPU usage.

In terminal, type top. Then, try the following in order:

z

Toggle color.

x

Toggle coloring of sort column.

s 9 9 Enter

Set update frequency to every 99 seconds.

Space

Force a update.

>

Change the sort column to the right of current sort column.

<

Change the sort column to the left.

R

Toggel reverse sort order.

O k Enter

Order by CPU usage. (also P)

O n Enter

Order by memory usage. (also M)

O a Enter

Order by pid.

O x Enter

Order by process name.

c

Show full path of commands.

k

Kill a process by pid.

u userName

Show only processes of a user.

h

Help.

q

Quit.

Summary Area

top - 12:59:21 up 20:59,  0 users,  load average: 1.05, 0.93, 0.90
      current     system                     past 1 min, 5 min, 15 min
      time        uptime

• If you have 1 CPU core, than load average of 1 means 100% CPU usage.
• If you have 2 CPU core, than load average of 2 means 100% CPU usage.
• If you have n CPU core, than load average of n means 100% CPU usage.

In general, “load average”/“number of cpu core” = CPU load. Higher than 1 means overloaded.

Tasks: 139 total,   1 running, 137 sleeping,   0 stopped,   1 zombie

Cpu(s):  5.4%us, 32.4%sy,  0.0%ni, 62.2%id,  0.0%wa,  0.0%hi,  0.0%si,  0.0%st
          user    system    niced     idle   IO wait

us = User CPU time

The time the CPU has spent running users' processes that are not niced.

sy = System CPU time

The time the CPU has spent running the kernel and its processes.

ni = Nice CPU time

The time the CPU has spent running users' proccess that have been niced. (see: man nice)

wa = iowait

Amount of time the CPU has been waiting for I/O to complete.

hi = Hardware IRQ

The amount of time the CPU has been servicing hardware interrupts.

si = Software Interrupts

The amount of time the CPU has been servicing software interrupts.

st = Steal Time

The amount of CPU “stolen” from this virtual machine by the hypervisor for other tasks (such as running another virtual machine).

Mem:    800340k total,   652680k used,   147660k free,    45688k buffers
Swap:   818172k total,     8584k used,   809588k free,   315372k cached

Actual free memory (RAM) available to programs is: free + buffers + cached. For detail, see: Linux: Show Free Memory .

Better is to see memory usage visually. Use htop. [see Linux: Monitor Processes, htop]

  PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND

PID

Process Id

USER

User Name

PR

Priority

NI

Nice value

VIRT

Virtual Image (kb)

RES

Resident size (kb)

SHR

Shared Mem size (kb)

S

Process Status

%CPU

CPU usage

%MEM

Memory usage (RES)

COMMAND

Command name/line

TIME+

CPU Time, hundredths

For some explanation of these, do man top.

Common Top Options

top -d 9

Run top with delay (update frequency) set to 9 seconds.

top -u john

Show only processes from user john.

top -n 10

Run top with 10 updates, then exit.

top -b -n 1 > top_out.txt

Dump top output as plain text to a file. The “-b” means batch mode. Basically, in batch mode, it dosn't accept any interactive inputs. If you run top -b, use Ctrl + c to exit.

Better top: htop

unix “top” is a very old program. It has some problems. For example, sometimes you want to view one particular process, but if you don't have a long screen, it's very diffucult or impossible, unless you find the pid first than call top -p pid.

A much better one is “htop”. See Linux: Monitor Processes, htop.