The top command is very easy to use but you should know the things in details. The output of to is :
top output:
top - 22:09:08 up 14 min, 1 user, load average: 0.21, 0.23, 0.30
Tasks: 81 total, 1 running, 80 sleeping, 0 stopped, 0 zombie
Cpu(s): 9.5%us, 31.2%sy, 0.0%ni, 27.0%id, 7.6%wa, 1.0%hi, 23.7%si, 0.0%st
Mem: 255592k total, 167568k used, 88024k free, 25068k buffers
Swap: 524280k total, 0k used, 524280k free, 85724k cached
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
3166 apache 15 0 29444 6112 1524 S 6.6 2.4 0:00.79 httpd
3161 apache 15 0 29444 6112 1524 S 5.9 2.4 0:00.79 httpd
3164 apache 15 0 29444 6112 1524 S 5.9 2.4 0:00.75 httpd
3169 apache 15 0 29444 6112 1524 S 5.9 2.4 0:00.74 httpd
3163 apache 15 0 29444 6112 1524 S 5.6 2.4 0:00.76 httpd
3165 apache 15 0 29444 6112 1524 S 5.6 2.4 0:00.77 httpd
3167 apache 15 0 29444 6112 1524 S 5.3 2.4 0:00.73 httpd
3162 apache 15 0 29444 6112 1524 S 5.0 2.4 0:00.77 httpd
3407 root 16 0 2188 1012 816 R 1.7 0.4 0:00.51 top
240 root 15 0 0 0 0 S 0.3 0.0 0:00.08 pdflush
501 root 10 -5 0 0 0 S 0.3 0.0 0:01.20 kjournald
2794 root 18 0 12720 1268 560 S 0.3 0.5 0:00.73 pcscd
1 root 15 0 2060 636 544 S 0.0 0.2 0:03.81 init
2 root RT -5 0 0 0 S 0.0 0.0 0:00.00 migration/0
3 root 34 19 0 0 0 S 0.0 0.0 0:00.00 ksoftirqd/0
4 root RT -5 0 0 0 S 0.0 0.0 0:00.00 watchdog/0
5 root 10 -5 0 0 0 S 0.0 0.0 0:00.07 events/0
The first line in top:
top - 22:09:08 up 14 min, 1 user, load average: 0.21, 0.23, 0.30
“22:09:08″ is the current time; “up 14 min” shows how long the system has been up for; “1 user” how many users are logged in; “load average: 0.21, 0.23, 0.30″ the load average of the system (1minute, 5 minutes, 15 minutes).
Load average is an extensive topic and to understand its inner workings can be daunting. The simplest of definitions states that load average is the cpu utilization over a period of time. A load average of 1 means your cpu is being fully utilized and processes are not having to wait to use a CPU. A load average above 1 indicates that processes need to wait and your system will be less responsive. If your load average is consistently above 3 and your system is running slow you may want to upgrade to more CPU’s or a faster CPU.
The second line in top:
Tasks: 82 total, 1 running, 81 sleeping, 0 stopped, 0 zombie
Shows the number of processes and their current state.
The third lin in top:
Cpu(s): 9.5%us, 31.2%sy, 0.0%ni, 27.0%id, 7.6%wa, 1.0%hi, 23.7%si, 0.0%st
Shows CPU utilization details. “9.5%us” user processes are using 9.5%; “31.2%sy” system processes are using 31.2%; “27.0%id” percentage of available cpu; “7.6%wa” time CPU is waiting for IO.
When first analyzing the Cpu(s) line in top look at the %id to see how much cpu is available. If %id is low then focus on %us, %sy, and %wa to determine what is using the CPU.
The fourth and fifth lines in top:
Mem: 255592k total, 167568k used, 88024k free, 25068k buffers
Swap: 524280k total, 0k used, 524280k free, 85724k cached
Describes the memory usage. These numbers can be misleading. “255592k total” is total memory in the system; “167568K used” is the part of the RAM that currently contains information; “88024k free” is the part of RAM that contains no information; “25068K buffers and 85724k cached” is the buffered and cached data for IO.
So what is the actual amount of free RAM available for programs to use ?
The answer is: free + (buffers + cached)
88024k + (25068k + 85724k) = 198816k
How much RAM is being used by progams ?
The answer is: used - (buffers + cached)
167568k - (25068k + 85724k) = 56776k
The processes information:
Top will display the process using the most CPU usage in descending order. Lets describe each column that represents a process.
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
3166 apache 15 0 29444 6112 1524 S 6.6 2.4 0:00.79 httpd
PID - process ID of the process
USER - User who is running the process
PR - The priority of the process
NI - Nice value of the process (higher value indicates lower priority)
VIRT - The total amount of virtual memory used
RES - Resident task size
SHR - Amount of shared memory used
S - State of the task. Values are S (sleeping), D (uninterruptible sleep), R (running), Z (zombies), or T (stopped or traced)
%CPU - Percentage of CPU used
%MEM - Percentage of Memory used
TIME+ - Total CPU time used
COMMAND - Command issued
Interacting with TOP
Now that we are able to understand the output from TOP lets learn how to change the way the output is displayed.
Just press the following key while running top and the output will be sorted in real time.
M - Sort by memory usage
P - Sort by CPU usage
T - Sort by cumulative time
z - Color display
k - Kill a process
q - quit
If we want to kill the process with PID 3161, then press “k” and a prompt will ask you for the PID number, and enter 3161.
Command Line Parameters with TOP
You can control what top displays by issuing parameters when you run top.
- d - Controls the delay between refreshes
- p - Specify the process by PID that you want to monitor
-n - Update the display this number of times and then exit
If we want to only monitor the http process with a PID of 3166
$ top -p 3166
If we want to change the delay between refreshes to 5 seconds
$ top -d 5
17 comments:
Nice Information, It's quite useful
Can you please also add for iostat and vmstat
Thanks
Commonly-used columns:
1. PID - Process ID - The unique ID of the process (commonly used with the kill command)
2. USER - Username which the process is running under
3. PR - Priority for the process (ranges from -20 for very important processes to 19 for unimportant processes)
4. NI - Nice value modifies the priority of the process (a negative value will increase the priority of the process and a positive value will decrease the priority of the process)
5. VIRT - Total amount of virtual memory used by the process
6. RES - Resident size (kb) - Non-swapped physical memory which the process has used
7. SHR - Shared memory size (kb) - Amount of shared memory which the process has used (shared memory is memory which could be allocated to other processes)
8. S - Process status - Possible values:
* R - Running
* D - Sleeping (may not be interrupted)
* S - Sleeping (may be interrupted)
* T - Traced or stopped
* Z - Zombie or "hung" process
9. %CPU - Percentage of CPU time the process was using at the time top last updated
10. %MEM - Percentage of memory (RAM) the process was using at the time top last updated
11. TIME+ - Cumulative CPU time which the process and children of the process have used
12. COMMAND - Name of the process or the path to the command used to start the process (press c to toggle between the name of the process and the path to the command used to start the process)
Thanks for this, you've saved me hours of digging around for info. Nice work :)
What can I do to see all processes? I mean if I have a small monitor?
I just read a comment from Manoj Mukundan on another site that's applicable here:
While using top, press "1" to show load of each cpu(core).
This cleared up the confusion of having one process at 99%+ and a CPU utilization of 39%. 4 cores of course!
Very useful information. Thanks!
Thank you for the nice information.
tks a lot for this info!
Thanks a lot for valuable info.
Excellent info. Could pls teel us how thi si sdifferent from ps command to check the process running?.
-Mohan
Thanks Mohan.
'ps' command showing all process by time wise. which is having the all process. Its not care about the process is running or sleeping.
whereas 'top' command showing running process in the top order. That's why you can see the some of the process in the first line after some time it will go second or third its dependencies on the process status.
S- sleeping process
R- Running process
D- going to die
Why not use htop?
http://www.linuxask.com/questions/a-better-alternative-to-top
Thanks, very clear and concise explanation. Sp we want the load averages to be as close to 0 as possible and the %id to be as close to 100 as possible. What is the significance of the Process %CPU & %MEM? Should we be concerned if the %CPU frequently hits 100%+ for a few seconds at a time? There is a WordPress site on my server that every time a page is clicked it goes to 100% (and the site is very slow). Should this be a concern?
Is there any way telling from the top output which account is causing high loads?
Thanks.
good one
that helps a lot
thank you
Thanks a lot.
Finally a good explanation of Top
Thanks, but, you didnt tell how to run the top command in first place? I need to know this urgently, but dont know how to execute TOP command. Plz help me!
Good bunch of information.For a process which is running how can we know about the amount of time it still needs to complete it?
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