Monitor IO in Linux 2016-09-30 06:49
There are a lot of tools to monitor IO in Linux. iotop is one of the most common command to monitor IO of each process. iostat is another common commands. I will show you how to use them in this blog.
iotop
The output of it is like following.
Total DISK READ: 0.00 B/s | Total DISK WRITE: 364.42 K/s
TID PRIO USER DISK READ DISK WRITE SWAPIN IO> COMMAND
9789 be/4 root 0.00 B/s 7.29 K/s 0.00 % 32.54 % java -Djava.util.logging.config.file=/opt/web_app/tomcat_sdpk~at_sdpk_8084/temp org.apache.catalina.startup.Bootstrap start
357 be/3 root 0.00 B/s 61.95 K/s 0.00 % 20.02 % [jbd2/sda3-8]
3404 be/4 root 0.00 B/s 3.64 K/s 0.00 % 0.00 % java -Djava.util.logging.config.file=/opt/web_app/tomcat_file~at_file_8082/temp org.apache.catalina.startup.Bootstrap start
1391 be/4 root 0.00 B/s 7.29 K/s 0.00 % 0.00 % [flush-8:0]
25723 be/4 root 0.00 B/s 7.29 K/s 0.00 % 0.00 % java -Djava.util.logging.config.file=/opt/web_app/tomcat_hd_8~mcat_hd_8189/temp org.apache.catalina.startup.Bootstrap start
1 be/4 root 0.00 B/s 0.00 B/s 0.00 % 0.00 % init
2 be/4 root 0.00 B/s 0.00 B/s 0.00 % 0.00 % [kthreadd]
3 rt/4 root 0.00 B/s 0.00 B/s 0.00 % 0.00 % [migration/0]
4 be/4 root 0.00 B/s 0.00 B/s 0.00 % 0.00 % [ksoftirqd/0]
5 rt/4 root 0.00 B/s 0.00 B/s 0.00 % 0.00 % [stopper/0]
6 rt/4 root 0.00 B/s 0.00 B/s 0.00 % 0.00 % [watchdog/0]
7 rt/4 root 0.00 B/s 0.00 B/s 0.00 % 0.00 % [migration/1]
8 rt/4 root 0.00 B/s 0.00 B/s 0.00 % 0.00 % [stopper/1]
9 be/4 root 0.00 B/s 0.00 B/s 0.00 % 0.00 % [ksoftirqd/1]
10 rt/4 root 0.00 B/s 0.00 B/s 0.00 % 0.00 % [watchdog/1]
11 be/4 root 0.00 B/s 0.00 B/s 0.00 % 0.00 % [events/0]
12 be/4 root 0.00 B/s 0.00 B/s 0.00 % 0.00 % [events/1]
13 be/4 root 0.00 B/s 0.00 B/s 0.00 % 0.00 % [events/0]
14 be/4 root 0.00 B/s 0.00 B/s 0.00 % 0.00 % [events/1]
15 be/4 root 0.00 B/s 0.00 B/s 0.00 % 0.00 % [events_long/0]
16 be/4 root 0.00 B/s 0.00 B/s 0.00 % 0.00 % [events_long/1]
17 be/4 root 0.00 B/s 0.00 B/s 0.00 % 0.00 % [events_power_ef]
18 be/4 root 0.00 B/s 0.00 B/s 0.00 % 0.00 % [events_power_ef]
19 be/4 root 0.00 B/s 0.00 B/s 0.00 % 0.00 % [cgroup]
20 be/4 root 0.00 B/s 0.00 B/s 0.00 % 0.00 % [khelper]
21 be/4 root 0.00 B/s 0.00 B/s 0.00 % 0.00 % [netns]
22 be/4 root 0.00 B/s 0.00 B/s 0.00 % 0.00 % [async/mgr]
23 be/4 root 0.00 B/s 0.00 B/s 0.00 % 0.00 % [pm]
24 be/4 root 0.00 B/s 0.00 B/s 0.00 % 0.00 % [sync_supers]
25 be/4 root 0.00 B/s 0.00 B/s 0.00 % 0.00 % [bdi-default]
26 be/4 root 0.00 B/s 0.00 B/s 0.00 % 0.00 % [kintegrityd/0]
27 be/4 root 0.00 B/s 0.00 B/s 0.00 % 0.00 % [kintegrityd/1]
28 be/4 root 0.00 B/s 0.00 B/s 0.00 % 0.00 % [kblockd/0]
29 be/4 root 0.00 B/s 0.00 B/s 0.00 % 0.00 % [kblockd/1]
There are a lot of processes do not read or write. If you want it only show the processes doing I/O use this command like this iotop -o. If you want monitor the specify process use it like this iotop -p 9789.
iostat
This command is different from iotop it will show you the overview of IO instead of every process's. The output of it is like following.
Linux 2.6.32-573.22.1.el6.x86_64 (localhost.localdomain) 09/30/2016 _x86_64_ (2 CPU)
avg-cpu: %user %nice %system %iowait %steal %idle
2.36 0.00 0.44 2.22 0.00 94.97
Device: tps Blk_read/s Blk_wrtn/s Blk_read Blk_wrtn
sda 8.73 138.39 196.54 242392164 344226556
It display the IO status in block by default, if you want it display in kilobytes use this command like this iostat -k. (iotop display the IO status in kilobytes by default.) We can use -x parameter to show extended IO information. The output of iostat -x -k is like following.
Linux 2.6.32-573.22.1.el6.x86_64 (localhost.localdomain) 09/30/2016 _x86_64_ (2 CPU)
avg-cpu: %user %nice %system %iowait %steal %idle
2.36 0.00 0.44 2.22 0.00 94.97
Device: rrqm/s wrqm/s r/s w/s rkB/s wkB/s avgrq-sz avgqu-sz await svctm %util
sda 0.96 18.02 2.19 6.54 69.18 98.25 38.35 0.25 28.47 5.91 5.16
"%util" in the far right of the output means the usage of this disk. 5.16% is very low for the single disk computer. If this value is larger than 100% in the single disk computer that means IO is busy now. If there are many disk in your computer this value may larger than 100% but that may not mean IO is busy.