Sar is part of Sysstat, a collection of performance monitoring tools for Linux.
Run sar 2
where interval in seconds measurements will taken shown at. sar outputs a variety of performance data. See the man page for information on all of the available diagnostics. For monitoring I/O you may use the -b
or -d
flags to view I/O transfer rates or block device activity respectively.
The feature that sets sar apart from tools like iotop is it's logging capability. Once logging is set up you may use sar -A
to view all information in the current days logfile or use -f
to specify a specific logfile you want to examine.
To make use of sar you first need to enable logging. When building from source make install –enable-install-cron
can be used to enable logging via cron. When installing a package, depending on your distribution, logging might be enabled by default or you may have to use either your init-system or create a cron-job to activate it. For details view the sysstat-documentation or the relevant documentation for your distribution.
The default output when running sar
looks like this:
Linux 4.4.3-1-ARCH (your-hostname) 03/10/2016 _x86_64_ (8 CPU) 02:52:49 PM CPU %user %nice %system %iowait %steal %idle 02:52:51 PM all 8.02 0.00 1.13 0.00 0.00 90.86 02:52:53 PM all 8.57 0.00 0.69 0.06 0.00 90.68 02:52:55 PM all 8.43 0.00 1.00 0.00 0.00 90.57 02:52:57 PM all 7.66 0.00 0.69 0.00 0.00 91.65
sar -bd 2
results in this output:
Linux 4.4.3-1-ARCH (your-hostname) 03/10/2016 _x86_64_ (8 CPU) 03:25:29 PM tps rtps wtps bread/s bwrtn/s 03:25:31 PM 59.00 0.00 59.00 0.00 47068.00 03:25:29 PM DEV tps rd_sec/s wr_sec/s avgrq-sz avgqu-sz await svctm %util 03:25:31 PM dev8-0 59.00 0.00 47068.00 797.76 2.24 37.91 0.76 4.50 03:25:31 PM dev8-32 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 03:25:31 PM dev8-16 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 03:25:31 PM tps rtps wtps bread/s bwrtn/s 03:25:33 PM 1.00 0.00 1.00 0.00 52.00 03:25:31 PM DEV tps rd_sec/s wr_sec/s avgrq-sz avgqu-sz await svctm %util 03:25:33 PM dev8-0 1.00 0.00 52.00 52.00 0.00 0.00 0.00 0.00 03:25:33 PM dev8-32 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 03:25:33 PM dev8-16 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00