iostat(8) BSD System Manager's Manual iostat(8)

NAME

 iostat -- report I/O statistics

SYNOPSIS

 iostat [-CUdKIoT?] [-c count] [-n devs] [-w wait] [drives]

DESCRIPTION

 Iostat displays kernel I/O statistics on terminal, device and cpu opera-
 tions. The first statistics that are printed are averaged over the sys-
 tem uptime. To get information about the current activity, a suitable
 wait time should be specified, so that the subsequent sets of printed
 statistics will be averaged over that time.
 The options are as follows:
 -? Display a usage statement and exit.
 -C Display CPU statistics. This is on by default, unless -d is speci-
 fied.
 -c Repeat the display count times. If no wait interval is specified,
 the default is 1 second.
 -d Display only device statistics. If this flag is turned on, only
 device statistics will be displayed, unless -C or -U or -T is also
 specfied to enable the display of CPU, load average or TTY statis-
 tics.
 -I Display total statstics for a given time period, rather than aver-
 age statistics for each second during that time period.
 -K In the blocks transferred display (-o), display block count in
 kilobytes rather then the device native block size.
 -n Display up to devs number of devices. iostat will display fewer
 devices if there aren't devs devices present.
 -o Display old-style iostat device statistics. Sectors per second,
 transfers per second, and miliseconds per seek are displayed. If
 -I is specified, total blocks/sectors, total transfers, and
 miliseconds per seek are displayed.
 -T Display TTY statistics. This is on by default, unless -d is speci-
 fied.
 -U Display system load averages. This is on by default, unless -d is
 specified.
 -w Pause wait seconds between each display. If no repeat count is
 specified, the default is infinity.
 Iostat displays its information in the following format:
 tty
 tin characters read from terminals
 tout characters written to terminals
 devices
 Device operations. The header of the field is the device name and
 unit number. iostat will display as many devices as will fit in a
 standard 80 column screen, or the maximum number of devices in the
 system, whichever is smaller. If -n is specified on the command
 line, iostat will display the smaller of the requested number of
 devices, and the maximum number of devices in the system. To force
 iostat to display specific drives, their names may be supplied on
 the command line. iostat will not display more devices than will
 fit in an 80 column screen, unless the -n argument is given on the
 command line to specify a maximum number of devices to display, or
 the list of specified devices exceeds 80 columns. If fewer devices
 are specified on the command line than will fit in an 80 column
 screen, iostat will show only the specified devices.
 The standard iostat device display shows the following statistics:
 KB/t kilobytes per transfer
 tps transfers per second
 MB/s megabytes per second
 The standard iostat device display, with the -I flag specified,
 shows the following statistics:
 KB/t kilobytes per transfer
 xfrs total number of transfers
 MB total number of megabytes transferred
 The old-style iostat display (using -o) shows the following statis-
 tics:
 sps sectors transferred per second
 tps transfers per second
 msps average milliseconds per transaction
 The old-style iostat display, with the -I flag specified, shows the
 following statistics:
 blk total blocks/sectors transferred
 xfr total transfers
 msps average milliseconds per transaction
 cpu
 us % of cpu time in user mode
 sy % of cpu time in system mode
 id % of cpu time in idle mode

EXAMPLES

 iostat -w 1 disk0 disk2
 Display statistics for the first and third disk devices device every sec-
 ond ad infinitum.
 iostat -c 2
 Display the statistics for the first four devices in the system twice,
 with a one second display interval.
 iostat -Iw 3
 Display total statistics every three seconds ad infinitum.
 iostat -odICTw 2 -c 9
 Display total statistics using the old-style output format 9 times, with
 a two second interval between each measurement/display. The -d flag gen-
 erally disables the TTY and CPU displays, but since the -T and -C flags
 are given, the TTY and CPU displays will be displayed.

SEE ALSO

 fstat(1) , netstat(1) , nfsstat(1) , ps(1) , pstat(8) 
 The sections starting with ``Interpreting system activity'' in Installing
 and Operating 4.3BSD.

HISTORY

 This version of iostat first appeared in FreeBSD 3.0.
BSD September 27, 2001 BSD