When you need to see the running processes on your Linux in real time, you have top as your tool for that.
Top also displays other information besides the running processes, like free memory both physical and swap also.
- To monitor all processes in the system use the following command
$top
top - 14:13:05 up 0 min, 0 users, load average: 0.52, 0.58, 0.59
Tasks: 4 total, 1 running, 3 sleeping, 0 stopped, 0 zombie
%Cpu(s): 30.1 us, 41.5 sy, 0.0 ni, 24.9 id, 0.0 wa, 3.6 hi, 0.0 si, 0.0 st
KiB Mem : 16242768 total, 1189172 free, 14817120 used, 236476 buff/cache
KiB Swap: 21265404 total, 20457076 free, 808328 used. 1284792 avail Mem
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
1 root 20 0 8892 308 272 S 0.0 0.0 0:00.26 init
7 root 20 0 8900 216 172 S 0.0 0.0 0:00.01 init
8 krishna+ 20 0 15104 3628 3532 S 0.0 0.0 0:00.33 bash
22 krishna+ 20 0 15912 1964 1400 R 0.0 0.0 0:00.01 top
- The first line in top
top - 14:14:15 up 1 min, 0 users, load average: 0.52, 0.58, 0.59
“14:13:05″ is the current time; “up 1 day” shows how long the system has been up for; “0 user” how many users are logged in; “load average: 0.52, 0.58, 0.59″ the load average of the system (1minute, 5 minutes, 15 minutes).
- The second line in top
Tasks: 4 total, 1 running, 3 sleeping, 0 stopped, 0 zombie
Shows the number of processes and their current state.
- The third line in top:
%Cpu(s): 30.1 us, 41.5 sy, 0.0 ni, 24.9 id, 0.0 wa, 3.6 hi, 0.0 si, 0.0 st
Shows CPU utilization details. “30.1%us” user processes are using 9.5%; “41.5%sy” system processes are using 41.5%; “24.9%id” percentage of available cpu; “0.0%wa” time CPU is waiting for IO.
- The fourth and fifth lines in top
KiB Mem : 16242768 total, 1189172 free, 14817120 used, 236476 buff/cacheKiB Swap: 21265404 total, 20457076 free, 808328 used. 1284792 avail Mem
“16242768k total” is total memory in the system; “14817120K used” is the part of the RAM that currently contains information; “1189172k free” is the part of RAM that contains no information; “1189172k buffers and 1284792k cached” is the buffered and cached data for IO.
- By default, top starts by showing the following task's property
| Field | Description |
|---|---|
| PID | Process |
| ID | USER Effective User ID |
| PR | Dynamic priority |
| NI | Nice value, also known as base priority |
| VIRT | Virtual Size of the task. This includes the size of process's executable binary, the data area and all the loaded shared libraries. |
| RES | The size of RAM currently consumed by the task. Swapped out portion of the task is not included. |
| SHR | Some memory areas could be shared between two or more task, this field reflects that shared areas. The example of shared area are shared library and SysV shared memory. S Task status |
| %CPU | The percentage of CPU time dedicated to run the task since the last top's screen update. |
| %MEM | The percentage of RAM currently consumed by the task. |
| TIME+ | The total CPU time the task has been used since it started. "+" sign means it is displayed with hundredth of a second granularity. By default, TIME/TIME+ doesn't account the CPU time used by the task's dead children. |
| Command | Showing program names |
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.
| Options | Description |
|---|---|
| u | Display specific user process |
| d | change delay or set screen refresh interval |
| M | Sort by memory usage |
| P | Sort by CPU usage |
| T | Sort by cumulative time |
| z | Color display |
| k | Kill a process |
| q | quit |
| r | to renice a process |
| h | help |
- To kill the process with PID 40, then press “k” and a prompt will ask you for the PID number, and enter 40. When asked about signal number give 9 or 15.
Note : To learn about signal numbers
top - 16:48:19 up 6 min, 0 users, load average: 0.52, 0.58, 0.59
Tasks: 7 total, 1 running, 6 sleeping, 0 stopped, 0 zombie
%Cpu(s): 10.7 us, 9.5 sy, 0.0 ni, 79.3 id, 0.0 wa, 0.4 hi, 0.0 si, 0.0 st
KiB Mem : 16242768 total, 7097544 free, 8908748 used, 236476 buff/cache
KiB Swap: 21265404 total, 21159464 free, 105940 used. 7193164 avail Mem
PID to signal/kill [default pid = 1] 40 PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
1 root 20 0 8892 304 268 S 0.0 0.0 0:00.12 init
7 root 20 0 8900 212 168 S 0.0 0.0 0:00.00 init
8 krishna+ 20 0 15104 3608 3516 S 0.0 0.0 0:00.20 bash
23 root 20 0 8900 216 172 S 0.0 0.0 0:00.01 init
24 krishna+ 20 0 15104 3616 3524 S 0.0 0.0 0:00.12 bash
40 krishna+ 20 0 12196 784 540 S 0.0 0.0 0:00.00 cat
41 krishna+ 20 0 15912 1900 1336 R 0.0 0.0 0:00.01 top
top - 16:48:19 up 6 min, 0 users, load average: 0.52, 0.58, 0.59
Tasks: 7 total, 1 running, 6 sleeping, 0 stopped, 0 zombie
%Cpu(s): 10.7 us, 9.5 sy, 0.0 ni, 79.3 id, 0.0 wa, 0.4 hi, 0.0 si, 0.0 st
KiB Mem : 16242768 total, 7097544 free, 8908748 used, 236476 buff/cache
KiB Swap: 21265404 total, 21159464 free, 105940 used. 7193164 avail Mem
Send pid 44 signal [15/sigterm] 9 PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
1 root 20 0 8892 304 268 S 0.0 0.0 0:00.12 init
7 root 20 0 8900 212 168 S 0.0 0.0 0:00.00 init
8 krishna+ 20 0 15104 3608 3516 S 0.0 0.0 0:00.20 bash
23 root 20 0 8900 216 172 S 0.0 0.0 0:00.01 init
24 krishna+ 20 0 15104 3616 3524 S 0.0 0.0 0:00.12 bash
40 krishna+ 20 0 12196 784 540 S 0.0 0.0 0:00.00 cat
41 krishna+ 20 0 15912 1900 1336 R 0.0 0.0 0:00.01 top
- Display specific user process. using top command with
-uoption will display specific users process details.
$top -u krishnaprasadkv
top - 17:09:54 up 27 min, 0 users, load average: 0.52, 0.58, 0.59
Tasks: 6 total, 1 running, 5 sleeping, 0 stopped, 0 zombie
%Cpu(s): 10.8 us, 9.0 sy, 0.0 ni, 79.7 id, 0.0 wa, 0.5 hi, 0.0 si, 0.0 st
KiB Mem : 16242768 total, 7342616 free, 8663676 used, 236476 buff/cache
KiB Swap: 21265404 total, 21100212 free, 165192 used. 7438236 avail Mem
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
45 krishna+ 20 0 15920 1916 1348 R 100.0 0.0 0:00.06 top
8 krishna+ 20 0 15104 3600 3500 S 0.0 0.0 0:00.21 bash
24 krishna+ 20 0 15104 3612 3424 S 0.0 0.0 0:00.13 bash
- Change delay or set screen refresh interval in top. By default screen refresh interval is 3.0 seconds, same can be change pressing
doption in running top command and change it as desired as shown below
top - 17:19:41 up 37 min, 0 users, load average: 0.52, 0.58, 0.59
Tasks: 6 total, 1 running, 5 sleeping, 0 stopped, 0 zombie
%Cpu(s): 13.1 us, 13.5 sy, 0.0 ni, 73.1 id, 0.0 wa, 0.3 hi, 0.0 si, 0.0 st
KiB Mem : 16242768 total, 7471712 free, 8534580 used, 236476 buff/cache
KiB Swap: 21265404 total, 21098532 free, 166872 used. 7567332 avail Mem
Change delay from 3.0 to 2 PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
45 krishna+ 20 0 15920 1980 1412 R 0.5 0.0 0:01.34 top
8 krishna+ 20 0 15104 3600 3500 S 0.0 0.0 0:00.21 bash
24 krishna+ 20 0 15104 3612 3424 S 0.0 0.0 0:00.13 bash
- Highlight running process. Press
zoption in running top command will display running process in color which may help you to identified running process easily.
Tasks: 6 total, 1 running, 5 sleeping, 0 stopped, 0 zombie
%Cpu(s): 8.6 us, 10.8 sy, 0.0 ni, 80.4 id, 0.0 wa, 0.2 hi, 0.0 si, 0.0 st
KiB Mem : 16242768 total, 7525756 free, 8480536 used, 236476 buff/cache
KiB Swap: 21265404 total, 21100312 free, 165092 used. 7621376 avail Mem
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
45 krishna+ 20 0 15920 2004 1436 R 0.5 0.0 0:02.00 top
8 krishna+ 20 0 15104 3600 3500 S 0.0 0.0 0:00.21 bash
24 krishna+ 20 0 15104 3612 3424 S 0.0 0.0 0:00.13 bash
- Save top command results. To save the running top command results output to a file.
$ top -n 1 -b > top-output.txt
Krishnaprasadkv:~$ top -n 1 -b >top-output.txt
krishnaprasadkv:~$ cat top-output.txt
top - 17:26:19 up 44 min, 0 users, load average: 0.52, 0.58, 0.59
Tasks: 7 total, 1 running, 6 sleeping, 0 stopped, 0 zombie
%Cpu(s): 11.6 us, 8.7 sy, 0.0 ni, 79.2 id, 0.0 wa, 0.5 hi, 0.0 si, 0.0 st
KiB Mem : 16242768 total, 7679060 free, 8327232 used, 236476 buff/cache
KiB Swap: 21265404 total, 21100520 free, 164884 used. 7774680 avail Mem
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
1 root 20 0 8892 300 264 S 0.0 0.0 0:00.12 init
7 root 20 0 8900 212 168 S 0.0 0.0 0:00.00 init
8 krishna+ 20 0 15104 3596 3496 S 0.0 0.0 0:00.21 bash
23 root 20 0 8900 216 172 S 0.0 0.0 0:00.01 init
24 krishna+ 20 0 15104 3616 3504 S 0.0 0.0 0:00.20 bash
45 krishna+ 20 0 15920 2000 1432 S 0.0 0.0 0:02.85 top
48 krishna+ 20 0 15768 1796 1324 R 0.0 0.0 0:00.01 top
- Getting top command help. By pressing
hto obtain top command help.
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 <Esc> to continue