Overview
By the end of this article you should be able to answer the following questions:
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If you want to see how much load your machine is under, then we use the top command:
$ top
This gives real-time-updating output of:
top - 22:07:24 up 2:54, 2 users, load average: 0.00, 0.01, 0.05
Tasks: 128 total, 3 running, 125 sleeping, 0 stopped, 0 zombie
%Cpu(s): 0.0 us, 0.0 sy, 0.0 ni,100.0 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0 st
KiB Mem : 1017480 total, 392620 free, 297988 used, 326872 buff/cache
KiB Swap: 2097148 total, 2097148 free, 0 used. 560664 avail Mem
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
1 root 20 0 59592 7040 3928 S 0.0 0.7 0:03.67 systemd
2 root 20 0 0 0 0 S 0.0 0.0 0:00.00 kthreadd
3 root 20 0 0 0 0 S 0.0 0.0 0:00.17 ksoftirqd/0
5 root 0 -20 0 0 0 S 0.0 0.0 0:00.00 kworker/0:0H
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On the first line we have a “load average” entry, followed by 3 values.
These values shows the average number of processes in the queue (waiting to be allocated a cpu) in the last 1, 5, and 15 minutes respectively. If these values are successfully increasing then it means that the machine’s load is declining. However if it is successively increasing then it means that the machine load is increasing.
By default, the top command only lists the top 30 or so processes, order by cpu usage. If you want to use top to monitor certain processes, then you can do:
$ top -p {pid1},{pid2},{pid3},...etc
This will only list the process with the given pid values, which makes it easier to work with, when you are interested in some particular processes. .
Top is an interactive utility and While in “top” mode, if you then select “h”, you will find various options available:
Help for Interactive Commands - procps-ng version 3.3.10
Window 1:Def: Cumulative mode Off. System: Delay 3.0 secs; Secure mode Off.
Z,B,E,e Global: 'Z' colors; 'B' bold; 'E'/'e' summary/task memory scale
l,t,m Toggle Summary: 'l' load avg; 't' task/cpu stats; 'm' memory info
0,1,2,3,I Toggle: '0' zeros; '1/2/3' cpus or numa node views; 'I' Irix mode
f,F,X Fields: 'f'/'F' add/remove/order/sort; 'X' increase fixed-width
L,&,<,> . Locate: 'L'/'&' find/again; Move sort column: '<'/'>' left/right
R,H,V,J . Toggle: 'R' Sort; 'H' Threads; 'V' Forest view; 'J' Num justify
c,i,S,j . Toggle: 'c' Cmd name/line; 'i' Idle; 'S' Time; 'j' Str justify
x,y . Toggle highlights: 'x' sort field; 'y' running tasks
z,b . Toggle: 'z' color/mono; 'b' bold/reverse (only if 'x' or 'y')
u,U,o,O . Filter by: 'u'/'U' effective/any user; 'o'/'O' other criteria
n,#,^O . Set: 'n'/'#' max tasks displayed; Show: Ctrl+'O' other filter(s)
C,... . Toggle scroll coordinates msg for: up,down,left,right,home,end
k,r Manipulate tasks: 'k' kill; 'r' renice
d or s Set update interval
W,Y Write configuration file 'W'; Inspect other output 'Y'
q Quit
( commands shown with '.' require a visible task display window )
Press 'h' or '?' for help with Windows,
Type 'q' or to continue
There is also a tui version of the top command called htop. Which you need to install:
$ yum install htop
Then do:
$ htop
See also:
http://www.thegeekstuff.com/2010/01/15-practical-unix-linux-top-command-examples/