Updated: 2021/Apr/14

IOSTAT(8)                   System Manager's Manual                  IOSTAT(8)

     iostat - report I/O statistics

     iostat [-CdDITxy] [-c count] [-w wait] [drives]

     iostat displays kernel I/O statistics on terminal, disk and CPU
     operations.  By default, iostat displays one line of statistics averaged
     over the machine's run time.  The use of -c presents successive lines
     averaged over the wait period.  The -I option causes iostat to print raw,
     unaveraged values.

     Only the last disk option specified (-d, -D, or -x) is used.

     The options are as follows:

     -c count    Repeat the display count times.  Unless the -I flag is in
                 effect, the first display is for the time since a reboot and
                 each subsequent report is for the time period since the last
                 display.  If no wait interval is specified, the default is 1

     -C          Show CPU statistics.  This is enabled by default unless the
                 -d, -D, -T, or -x flags are used.

     -d          Show disk statistics.  This is the default.  Displays
                 kilobytes per transfer, number of transfers, and megabytes
                 transferred.  Use of this flag disables display of CPU and
                 tty statistics.

     -D          Show alternative disk statistics.  Displays kilobytes
                 transferred, number of transfers, and time spent in
                 transfers.  Use of this flag disables the default display.

     -I          Show the running total values, rather than an average.

     -T          Show tty statistics.  This is enabled by default unless the
                 -C, -d, or -D flags are used.

     -w wait     Pause wait seconds between each display.  If no repeat count
                 is specified, the default is infinity.

     -x          Show extended disk statistics.  Each disk is displayed on a
                 line of its own with all available statistics.  This option
                 overrides all other display options, and all disks are
                 displayed unless specific disks are provided as arguments.
                 Additionally, separate read and write statistics are

     -y          Shows the extended statistics and additional queuing

     iostat displays its information in the following format:

           tin     characters read from terminals
           tout    characters written to terminals

           Disk operations.  The header of the field is the disk name and unit
           number.  If more drives are configured in the system that fit
           across the current display, iostat displays only those drives that
           fit on the display.  To force iostat to display specific drives,
           they may be supplied on the command line, either as names or
           fnmatch() patterns.

           KB/t    Kilobytes transferred per disk transfer
           t/s     transfers per second
           MB/s    Megabytes transferred per second
           The alternative display format, (selected with -D), presents the
           following values.
           KB      Kilobytes transferred
           xfr     Disk transfers
           time    Seconds spent in disk activity
           With the -y flag, the following queuing measurements are added
           wait    Number of I/O requests queued up
           actv    Number of currently active I/O requests
           wsvc_t  Average waiting time of an I/O request in milliseconds
           asvc_t  Average duration of an I/O request in milliseconds
           wtime   Seconds spent in the waiting queue.  Queuing data might not
                   be available from all drivers and is then shown as zeros.

           us      % of CPU time in user mode
           ni      % of CPU time in user mode running niced processes
           sy      % of CPU time in system mode
           in      % of CPU time in interrupt mode
           id      % of CPU time in idle mode

     fstat(1), netstat(1), nfsstat(1), ps(1), systat(1), vmstat(1),
     fnmatch(3), pstat(8)

     The sections starting with ``Interpreting system activity'' in Installing
     and Operating 4.3BSD.

     iostat appeared in Version 6 AT&T UNIX.  The -x option was added in
     NetBSD 1.4.  Collection of queueing values and the -y option were added
     in NetBSD 8.0.

NetBSD 9.99                      July 29, 2018                     NetBSD 9.99