Use top command in Linux 2016-09-29 06:05
We often use top command to see the tasks in Linux. There are many numbers in the output of top. In this page I will shortly introduce them. The output of top command is like following.
top - 14:46:30 up 197 days, 20:44, 4 users, load average: 0.05, 0.06, 0.02
Tasks: 103 total, 2 running, 101 sleeping, 0 stopped, 0 zombie
Cpu(s): 0.9%us, 0.0%sy, 0.0%ni, 98.7%id, 0.4%wa, 0.0%hi, 0.0%si, 0.0%st
Mem: 5993172k total, 5867316k used, 125856k free, 147540k buffers
Swap: 16777208k total, 0k used, 16777208k free, 3167192k cached
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
6372 root 20 0 1780m 50m 1896 S 13.6 0.9 641:32.67 mqttmsg
30959 root 20 0 2880m 919m 14m S 1.7 15.7 12:27.13 java
24781 root 20 0 1611m 151m 2208 S 1.3 2.6 51:12.51 mqttmsg
1430 root 20 0 1173m 11m 1240 S 1.0 0.2 1894:19 authserver
9765 root 20 0 850m 4584 1252 S 0.7 0.1 186:36.71 authserver
1 root 20 0 19232 1112 820 S 0.0 0.0 0:02.60 init
2 root 20 0 0 0 0 S 0.0 0.0 0:00.00 kthreadd
3 root RT 0 0 0 0 S 0.0 0.0 0:03.49 migration/0
4 root 20 0 0 0 0 S 0.0 0.0 7:41.93 ksoftirqd/0
5 root RT 0 0 0 0 S 0.0 0.0 0:00.00 migration/0
6 root RT 0 0 0 0 S 0.0 0.0 0:10.21 watchdog/0
7 root RT 0 0 0 0 S 0.0 0.0 0:04.88 migration/1
8 root RT 0 0 0 0 S 0.0 0.0 0:00.00 migration/1
9 root 20 0 0 0 0 S 0.0 0.0 14:00.37 ksoftirqd/1
10 root RT 0 0 0 0 S 0.0 0.0 0:11.88 watchdog/1
11 root 20 0 0 0 0 R 0.0 0.0 68:12.03 events/0
12 root 20 0 0 0 0 S 0.0 0.0 5:05.46 events/1
13 root 20 0 0 0 0 S 0.0 0.0 0:00.00 cgroup
14 root 20 0 0 0 0 S 0.0 0.0 0:01.52 khelper
15 root 20 0 0 0 0 S 0.0 0.0 0:00.00 netns
16 root 20 0 0 0 0 S 0.0 0.0 0:00.00 async/mgr
17 root 20 0 0 0 0 S 0.0 0.0 0:00.00 pm
18 root 20 0 0 0 0 S 0.0 0.0 0:19.03 sync_supers
19 root 20 0 0 0 0 S 0.0 0.0 0:22.28 bdi-default
20 root 20 0 0 0 0 S 0.0 0.0 0:00.00 kintegrityd/0
21 root 20 0 0 0 0 S 0.0 0.0 0:00.00 kintegrityd/1
22 root 20 0 0 0 0 S 0.0 0.0 1:35.37 kblockd/0
23 root 20 0 0 0 0 S 0.0 0.0 0:10.58 kblockd/1
24 root 20 0 0 0 0 S 0.0 0.0 0:00.00 kacpid
25 root 20 0 0 0 0 S 0.0 0.0 0:00.00 kacpi_notify
26 root 20 0 0 0 0 S 0.0 0.0 0:00.00 kacpi_hotplug
27 root 20 0 0 0 0 S 0.0 0.0 0:00.00 ata_aux
28 root 20 0 0 0 0 S 0.0 0.0 0:00.00 ata_sff/0
29 root 20 0 0 0 0 S 0.0 0.0 0:00.00 ata_sff/1
30 root 20 0 0 0 0 S 0.0 0.0 0:00.00 ksuspend_usbd
31 root 20 0 0 0 0 S 0.0 0.0 0:00.00 khubd
32 root 20 0 0 0 0 S 0.0 0.0 0:00.00 kseriod
33 root 20 0 0 0 0 S 0.0 0.0 0:00.00 md/0
34 root 20 0 0 0 0 S 0.0 0.0 0:00.00 md/1
35 root 20 0 0 0 0 S 0.0 0.0 0:00.00 md_misc/0
First line: this line shows this computer has been running 197 days 14 hours 46 minutes and 30 seconds. Maybe our computer won't keep running for such long time. But for a server it might be running several years. The time now is 20:44. 4 users means there are 4 users are operating this computer. load average show how busy the CPU is (maybe there are more than one CPUs in your environment). There are 3 numbers to show the load average in recent 1, 5 and 15 minutes. The smaller load average number means the lower resource usage.
Second line: this line shows the total tasks in this computer. How many tasks are running, sleeping or stopped right now? Now, there are 103 tasks need to be handled, but only one task is running. Most tasks are sleeping.
Third line: This line shows the percentage of different kind of tasks use CPU. 0.9%us means user program take 0.9% time of CPU. 0.4%wa means IO take 0.4% time of CPU. 98.7%id means 98.7% time of CPU is idle.
Fourth line: This line shows the memory usage. Total memory is 5993172k, 5867316k is used, and 125856k is free and 147540k in buffers. If in Windows free memory remain 125856/5993172 = 2%, you have to close some programs or add more memory. But in Linux is different from Windows. You can calculate the "free" memory in this way. Free memory = 125856k free + 147540k buffers + 3167192k cached = 3440588k. The free memory remain 3440588/5993172=57.4%.
Fifth line:This line shows the usage of swap. OS will transfer some memory data which is not used recently to swap. For more detail of swap size of CentOS click here. If the size of used swap changes frequently means data is transferred between memory and swap frequently. You need add more memory to your server.
The Rest: Shows every process detail every line. You can get the memory used and CPU time used. If the used CPU percentage larger than 100% means there are two CPUs or CPU cores in your computer and all of them are busy.