The
utility displays kernel
I/O
statistics on terminal, device and cpu operations.
The first statistics that are printed are averaged over the system 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:
-c
Repeat the display
count
times.
If no
wait
interval is specified, the default is 1 second.
-C
Display CPU statistics.
This is on by default, unless
-d
is specified.
-d
Display only device statistics.
If this flag is turned on, only device statistics will be displayed, unless
-C
or
-T
is also specified to enable the display of CPU or TTY statistics.
-h
Put
in
`top'
mode.
In this mode,
will show devices in order from highest to lowest bytes
per measurement cycle.
-I
Display total statistics for a given time period, rather than average
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.
-M
Extract values associated with the name list from the specified core
instead of the default
``/dev/kmem
''
-n
Display up to
devs
number of devices.
The
utility will display fewer devices if there are not
devs
devices present.
-N
Extract the name list from the specified system instead of the default
``/boot/kernel/kernel
''
-o
Display old-style
device statistics.
Sectors per second, transfers per second, and milliseconds per seek are
displayed.
If
-I
is specified, total blocks/sectors, total transfers, and
milliseconds per seek are displayed.
-t
Specify which types of devices to display.
There are three different categories of devices:
device type:
da
Direct Access devices
sa
Sequential Access devices
printer
Printers
proc
Processor devices
worm
Write Once Read Multiple devices
cd
CD devices
scanner
Scanner devices
optical
Optical Memory devices
changer
Medium Changer devices
comm
Communication devices
array
Storage Array devices
enclosure
Enclosure Services devices
floppy
Floppy devices
interface:
IDE
Integrated Drive Electronics devices
SCSI
Small Computer System Interface devices
other
Any other device interface
passthrough:
pass
Passthrough devices
The user must specify at least one device type, and may specify at most
one device type from each category.
Multiple device types in a single device type statement must be separated by
commas.
Any number of
-t
arguments may be specified on the command line.
All
-t
arguments are ORed together to form a matching expression against which
all devices in the system are compared.
Any device that fully matches any
-t
argument will be included in the
output, up to the number of devices that can be displayed in
80 columns, or the maximum number of devices specified by the user.
-T
Display TTY statistics.
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.
-x
Show extended disk statistics.
Each disk is displayed on a line of its own with all available statistics.
-z
If
-x
is specified, omit lines for devices with no activity.
-?
Display a usage statement and exit.
The
utility 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.
The
utility
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,
will display the smaller of the
requested number of devices, and the maximum number of devices in the system.
To force
to display specific drives, their names may be supplied on the command
line.
The
utility
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.
If fewer devices are specified on the command line than will fit in an 80
column screen,
will show only the specified devices.
The standard
device display shows the following statistics:
KB/t
kilobytes per transfer
tps
transfers per second
MB/s
megabytes per second
The standard
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 extended
device display, with the
-x
flag specified, shows the following statistics:
r/s
read operations per second
w/s
write operations per second
kr/s
kilobytes read per second
kw/s
kilobytes write per second
wait
transactions queue length
svc_t
average duration of transactions, in milliseconds
%b
% of time the device had one or more outstanding transactions
The old-style
display (using
-o
shows the following statistics:
sps
sectors transferred per second
tps
transfers per second
msps
average milliseconds per transaction
The old-style
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
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
FILES
/boot/kernel/kernel
Default kernel namelist.
/dev/kmem
Default memory file.
EXAMPLES
iostat -w 1 da0 da1 cd0
Display statistics for the first two Direct Access devices and the first
CDROM device every second ad infinitum.
iostat -c 2
Display the statistics for the first four devices in the system twice, with
a one second display interval.
iostat -t da -t cd -w 1
Display statistics for all CDROM and Direct Access devices every second
ad infinitum.
iostat -t da,scsi,pass -t cd,scsi,pass
Display statistics once for all SCSI passthrough devices that provide access
to either Direct Access or CDROM devices.
iostat -h -n 8 -w 1
Display up to 8 devices with the most I/O every second ad infinitum.
iostat -dh -t da -w 1
Omit the TTY and CPU displays, show devices in order of performance and
show only Direct Access devices every second ad infinitum.
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 generally disables the TTY and CPU displays, but since the
-T
and
-C
flags are given, the TTY and CPU displays will be displayed.
The use of
as a debugging tool for crash dumps is probably limited because there is
currently no way to get statistics that only cover the time immediately before
the crash.
