IOSTAT(1)

NAME
iostat - Report Central Processing Unit (CPU) statistics and input/output statistics for devices and partitions.

SYNOPSIS
iostat [ -c | -d ] [ -k ] [ -t ] [ -V ] [ -x [ device ] ] [ 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.

The first report generated by the iostat command provides statistics concerning the time since the system was booted. Each subsequent report covers the time since the previous report. All statistics are reported each time the iostat command is run. The report consists of a CPU header row followed by a row of CPU statistics. On multiprocessor systems, CPU statistics are calculated system-wide as averages among all processors. A device header row is displayed followed by a line of statistics for each device that is configured.

The interval parameter specifies the amount of time in seconds between each report. The first report contains statistics for the time since system startup (boot). Each subsequent report contains statistics collected during the interval since the previous report. The count parameter can be specified in conjunction with the interval parameter. If the count parameter is specified, the value of count determines the number of reports generated at interval seconds apart. If the interval parameter is specified without the count parameter, the iostat command generates reports continuously.

REPORTS
The iostat command generates two types of reports, the CPU Utilization report and the Device Utilization 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:

    %user
        Show the percentage of CPU utilization that occurred while executing at the user level (application).
    %nice
        Show the percentage of CPU utilization that occurred while executing at the user level with nice priority.
    %sys
        Show the percentage of CPU utilization that occurred while executing at the system level (kernel).
    %idle
        Show the percentage of time that the CPU or CPUs were idle.

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. The report may show the following fields, depending on whether -x and -k options are used or not:

    Device:
        This column gives the device name, which is displayed as hdiskn with 2.2 kernels, for the nth device. It is displayed as devm-n with newer kernels, where m is the major number of the device, and n a distinctive number. When -x option is used, the device name as listed in the /dev directory is displayed.

    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
        Indicate the amount of data read from the drive expressed in a number of blocks per second. Blocks are equivalent to sectors with post 2.4 kernels and therefore have a size of 512 bytes. With older kernels, a block is of indeterminate size.

    Blk_wrtn/s
        Indicate the amount of data written to the drive expressed in a number of blocks per second.

    Blk_read
        The total number of blocks read.

    Blk_wrtn
        The total number of blocks written.

    kB_read/s
        Indicate the amount of data read from the drive expressed in kilobytes per second. Data displayed are valid only with kernels 2.4 and later.

    kB_wrtn/s
        Indicate the amount of data written to the drive expressed in kilobytes per second. Data displayed are valid only with kernels 2.4 and later.

    kB_read
        The total number of kilobytes read. Data displayed are valid only with kernels 2.4 and later.

    kB_wrtn
        The total number of kilobytes written. Data displayed are valid only with kernels 2.4 and later.

    rrqm/s
        The number of read requests merged per second that were issued to the device.

    wrqm/s
        The number of write requests merged per second that were issued to the device.

    r/s
        The number of read requests that were issued to the device per second.

    w/s
        The number of write requests that were issued to the device per second.

    rsec/s
        The number of sectors read from the device per second.

    wsec/s
        The number of sectors written to the device per second.

    rkB/s
        The number of kilobytes read from the device per second.

    wkB/s
        The number of kilobytes 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.

    svctm
        The average service time (in milliseconds) for I/O requests that were issued to the device.

    %util
        Percentage of CPU time during which I/O requests were issued to the device.

OPTIONS

-c  The -c option is exclusive of the -d option and displays only the cpu usage report.

-d  The -d option is exclusive of the -c option and displays only the device utilization report.

-k  Display statistics in kilobytes per second instead of blocks per second. Data displayed are valid only with kernels 2.4 and later.

-t  Print the time for each report displayed.

-V  Print version number and usage then exit.

-x device
    Display extended statistics. If no device is given on the command line, then extended statistics are displayed for every device registered in the /proc/partitions file. Please note that Linux kernel needs to be patched for this option to work.

ENVIRONMENT
The iostat command takes into account the following environment variable:

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 format (YYYY-MM-DD) instead.

EXAMPLES
iostat
    Display 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.

BUGS
/proc filesystem must be mounted for iostat to work.

FILE
/proc/stat contains system statisitics.

/proc/partitions contains statistics for the devices.

AUTHOR
Sebastien Godard <sebastien.godard@wanadoo.fr>

SEE ALSO
vmstat(8), sar(1), mpstat(1)

http://perso.wanadoo.fr/sebastien.godard/