iostat command behaves contrary to the man page

[Lieven]

Ubuntu 18.10 cosmic

The iostat man page states the following:

[code]The first report generated by the iostat command provides statistics concerning the time since the system was booted, unless the -y option is used (in this case, this first report is omitted)[/code]

When entering the command [code]iostat -y[/code], i get only the first report generated by the iostat command, while it should display anything but the first report.

This seems to be a bug in version 12 of the sysstat package, because this problem did not happen with earlier versions.

Can something be done about this wrong behaviour?

[Karl Stenerud (kstenerud)]

Hi Lieven,

I've tried running with the -y options but haven't been able to reproduce this issue. The first entry is stats since system boot. With -y, it gives stats since the last report. Both bionic and cosmic behave the same way in this regard, as can be seen in the tps value in the first entry:

Setup:

# apt update && apt dist-upgrade -y && apt install -y sysstat

-------------------

On bionic:

root@tester:~# iostat mmcblk0 1
Linux 4.15.0-39-generic (tester) 11/20/18 _x86_64_ (4 CPU)

avg-cpu: %user %nice %system %iowait %steal %idle
          25.83 0.10 5.05 0.13 0.00 68.88

Device tps kB_read/s kB_wrtn/s kB_read kB_wrtn
mmcblk0 0.12 4.93 0.00 11668 0

^C
root@tester:~#
root@tester:~#
root@tester:~# iostat -y mmcblk0 1
Linux 4.15.0-39-generic (tester) 11/20/18 _x86_64_ (4 CPU)

avg-cpu: %user %nice %system %iowait %steal %idle
          36.11 0.00 5.56 0.00 0.00 58.33

Device tps kB_read/s kB_wrtn/s kB_read kB_wrtn
mmcblk0 0.00 0.00 0.00 0 0

^C

-----------------

On cosmic:

root@c:~# iostat mmcblk0 1
Linux 4.15.0-39-generic (c) 11/20/18 _x86_64_ (4 CPU)

avg-cpu: %user %nice %system %iowait %steal %idle
          26.26 0.10 5.11 0.13 0.00 68.39

Device tps kB_read/s kB_wrtn/s kB_read kB_wrtn
mmcblk0 1.03 42.28 0.00 11668 0

^C
root@c:~#
root@c:~#
root@c:~# iostat -y mmcblk0 1
Linux 4.15.0-39-generic (c) 11/20/18 _x86_64_ (4 CPU)

avg-cpu: %user %nice %system %iowait %steal %idle
           0.00 0.00 0.00 0.00 0.00 0.00

Device tps kB_read/s kB_wrtn/s kB_read kB_wrtn
mmcblk0 0.00 0.00 0.00 0 0

^C

-----------------

I can't proceed any further on this unless we have a reliable reproduction case. Please add a repro case in a comment and then change the status back from "invalid" to "new".

Thanks!

[Lieven (lieven-debels)]

Hi Karl

I executed the following commands both on cosmic and bionic:
iostat 1 5
iostat -y 1 5

As you can see from my attachment (iostat.txt) the -y command behaves different, or even erratic on cosmic.

Let me know if you need more info.

[Lieven (lieven-debels)]

Well, actually I installed the bionic version on cosmic, so I downgraded sysstat from version 12 to version 11.