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IOSTAT(1) | Linux User's Manual | IOSTAT(1) |
NAME¶
iostat - Report Central Processing Unit (CPU) statistics and input/output statistics for devices and partitions.SYNOPSIS¶
iostat [ -c ] [ -d ] [ -h ] [ -N ] [ -k | -m ] [ -t ] [ -V ] [ -x ] [ -z ] [ [ [ -T ] -g group_name ] { device [...] | ALL } ] [ -p [ device [,...] | ALL ] ] [ interval [ count ] ]DESCRIPTION¶
The iostat command is used for monitoring system input/output device loading by observing the time the devices are active in relation to their average transfer rates. The iostat command generates reports that can be used to change system configuration to better balance the input/output load between physical disks.REPORTS¶
The iostat command generates three types of reports, the CPU Utilization report, the Device Utilization report and the Network Filesystem report.- CPU Utilization Report
- The first report generated by the iostat command is
the CPU Utilization Report. For multiprocessor systems, the CPU values are
global averages among all processors. The report has the following format:
Show the percentage of CPU utilization that
occurred while executing at the user level (application).
Show the percentage of CPU utilization that
occurred while executing at the user level with nice priority.
Show the percentage of CPU utilization that
occurred while executing at the system level (kernel).
Show the percentage of time that the CPU or
CPUs were idle during which the system had an outstanding disk I/O
request.
Show the percentage of time spent in
involuntary wait by the virtual CPU or CPUs while the hypervisor was servicing
another virtual processor.
Show the percentage of time that the CPU or
CPUs were idle and the system did not have an outstanding disk I/O
request.
- Device Utilization Report
- The second report generated by the iostat command is
the Device Utilization Report. The device report provides statistics on a
per physical device or partition basis. Block devices and partitions for
which statistics are to be displayed may be entered on the command line.
If no device nor partition is entered, then statistics are displayed for
every device used by the system, and providing that the kernel maintains
statistics for it. If the ALL keyword is given on the command line,
then statistics are displayed for every device defined by the system,
including those that have never been used. Transfer rates are shown in 1K
blocks by default, unless the environment variable POSIXLY_CORRECT is set,
in which case 512-byte blocks are used. The report may show the following
fields, depending on the flags used:
This column gives the device (or partition)
name as listed in the /dev directory.
tps
Indicate the number of transfers per second
that were issued to the device. A transfer is an I/O request to the device.
Multiple logical requests can be combined into a single I/O request to the
device. A transfer is of indeterminate size.
Blk_read/s (kB_read/s, MB_read/s)
Indicate the amount of data read from the
device expressed in a number of blocks (kilobytes, megabytes) per second.
Blocks are equivalent to sectors and therefore have a size of 512 bytes.
Blk_wrtn/s (kB_wrtn/s, MB_wrtn/s)
Indicate the amount of data written to the
device expressed in a number of blocks (kilobytes, megabytes) per second.
Blk_read (kB_read, MB_read)
The total number of blocks (kilobytes,
megabytes) read.
Blk_wrtn (kB_wrtn, MB_wrtn)
The total number of blocks (kilobytes,
megabytes) written.
rrqm/s
The number of read requests merged per second
that were queued to the device.
wrqm/s
The number of write requests merged per second
that were queued to the device.
r/s
The number (after merges) of read requests
completed per second for the device.
w/s
The number (after merges) of write requests
completed per second for the device.
rsec/s (rkB/s, rMB/s)
The number of sectors (kilobytes, megabytes)
read from the device per second.
wsec/s (wkB/s, wMB/s)
The number of sectors (kilobytes, megabytes)
written to the device per second.
avgrq-sz
The average size (in sectors) of the requests
that were issued to the device.
avgqu-sz
The average queue length of the requests that
were issued to the device.
await
The average time (in milliseconds) for I/O
requests issued to the device to be served. This includes the time spent by
the requests in queue and the time spent servicing them.
r_await
The average time (in milliseconds) for read
requests issued to the device to be served. This includes the time spent by
the requests in queue and the time spent servicing them.
w_await
The average time (in milliseconds) for write
requests issued to the device to be served. This includes the time spent by
the requests in queue and the time spent servicing them.
svctm
The average service time (in milliseconds) for
I/O requests that were issued to the device. Warning! Do not trust this field
any more. This field will be removed in a future sysstat version.
%util
Percentage of CPU time during which I/O
requests were issued to the device (bandwidth utilization for the device).
Device saturation occurs when this value is close to 100%.
OPTIONS¶
- -c
- Display the CPU utilization report.
- -d
- Display the device utilization report.
- -g group_name { device [...] | ALL }
- Display statistics for a group of devices. The iostat command reports statistics for each individual device in the list then a line of global statistics for the group displayed as group_name and made up of all the devices in the list. The ALL keyword means that all the block devices defined by the system shall be included in the group.
- -h
- Make the Device Utilization Report easier to read by a human.
- -k
- Display statistics in kilobytes per second.
- -m
- Display statistics in megabytes per second.
- -N
- Display the registered device mapper names for any device mapper devices. Useful for viewing LVM2 statistics.
- -p [ { device [,...] | ALL } ]
- The -p option displays statistics for block devices and all their partitions that are used by the system. If a device name is entered on the command line, then statistics for it and all its partitions are displayed. Last, the ALL keyword indicates that statistics have to be displayed for all the block devices and partitions defined by the system, including those that have never been used.
- -T
- This option must be used with option -g and indicates that only global statistics for the group are to be displayed, and not statistics for individual devices in the group.
- -t
- Print the time for each report displayed. The timestamp format may depend on the value of the S_TIME_FORMAT environment variable (see below).
- -V
- Print version number then exit.
- -x
- Display extended statistics.
- -z
- Tell iostat to omit output for any devices for which there
was no activity during the sample period.
ENVIRONMENT¶
The iostat command takes into account the following environment variables:- S_TIME_FORMAT
- If this variable exists and its value is ISO then
the current locale will be ignored when printing the date in the report
header. The iostat command will use the ISO 8601 format
(YYYY-MM-DD) instead. The timestamp displayed with option -t will also be
compliant with ISO 8601 format.
- POSIXLY_CORRECT
- When this variable is set, transfer rates are shown in
512-byte blocks instead of the default 1K blocks.
EXAMPLES¶
iostatDisplay a single history since boot report for
all CPU and Devices.
iostat -d 2
Display a continuous device report at two
second intervals.
iostat -d 2 6
Display six reports at two second intervals
for all devices.
iostat -x sda sdb 2 6
Display six reports of extended statistics at
two second intervals for devices sda and sdb.
iostat -p sda 2 6
Display six reports at two second intervals
for device sda and all its partitions (sda1, etc.)
BUGS¶
/proc filesystem must be mounted for iostat to work.FILES¶
/proc/stat contains system statistics.AUTHOR¶
Sebastien Godard (sysstat <at> orange.fr)SEE ALSO¶
sar(1), pidstat(1), mpstat(1), vmstat(8), nfsiostat(1), cifsiostat(1)MAY 2012 | Linux |