Top command usages and examples in Unix/Linux

Top command has an important role in Unix/Linux system/server administration side. The command “top” displays a dynamic view of process that are currently running under the system. Here I’m  explaining some of the useful usage of top command for my Admin friends.

Top command is simple in usage and very interesting also. The simple top command output is shown below.

1. top

An important thing that we can observe is the dynamic view of Load Average from “top” command and also uptime, total users logged in to the system, cpu & free memory details etc..

Some useful switches 

2. “-d” switch with top command

d means delay time. The syntax for ‘d’ is “top -d ss.tt”(seconds.tenths).

For example top -d 05.00 that means the top command’s output screen have a dynamic change with 5 second time interval. You can speedup or slowdown the top display frequency by using this switch.

3. top command’s output field description.

PID : Process ID.

USER : The user name who runs the process.

PR : Priority

NI : Nice value

%CPU : CPU usage

TIME : CPU Time

%MEM : Memory usage (RES)

VIRT : Virtual Image (kb)

SWAP : Swapped size (kb)

RES : Resident size (kb)

S : Process Status

The status of the task which can be one of:

'D' = uninterruptible sleep

'R' = running

'S' = sleeping

'T' = traced or stopped

'Z' = zombie

4. Interactive commands for top

Several single-key commands are recognised while top is running. Some of the useful hotkeys are explained below:

4.1 space

Immediately updates the display.

4.2 h or ?

This will display the help page (q for quit).

4.3 k :

For kill a process.

In the image change PROCESS ID with the pid of process which you want to kill.

4.4 i

Ignore idle and zombie processes. This is a toggle switch.

4.5 I (shift i)

Toggle between Solaris (CPU percentage divided by total number of CPUs) and Irix (CPU percentage calculated solely by amount of time) views. This is a toggle switch that affects only SMP systems.

4.6 n or #

Change the number of processes to show. You will be prompted to enter the number. This overrides automatic determination of the number of processes to show, which is based on window size measurement. If 0 is specified, then top will show as many processes as will fit on the screen; this is the default.

4.7 q

Quit.

4.8 M (shift m)

sort tasks by resident memory usage.

4.9 T (shift t)

sort tasks by time / cumulative time.

4.10 c or P(shift p)

sort tasks by CPU usage (default).

4.11 A (shift a)

sort tasks by age (newest first).

4.12 N (shift n)

sort tasks by pid (numerically).

These are some interesting usage of top command under UNIX/LINUX.