On Apache
Under GNU General Public License
2012-05-26 00:34 @38.107.179.238 Crawled by CCBot/1.0 (+http://www.commoncrawl.org/bot.html)
IOSTAT(1) Linux User's Manual IOSTAT(1)
NAME
iostat - Report Central Processing Unit (CPU) statistics and input/output statistics for
devices, partitions and network filesystems (NFS).
SYNOPSIS
iostat [ -c ] [ -d ] [ -N ] [ -n ] [ -h ] [ -k | -m ] [ -t ] [ -V ] [ -x ] [ 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 bal-
ance 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 con-
sists 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 config-
ured. When option -n is used, an NFS header row is displayed followed by a line of
statistics for each network filesystem that is mounted.
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 parame-
ter, the iostat command generates reports continuously.
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:
%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.
%system
Show the percentage of CPU utilization that occurred while executing at the
system level (kernel).
%iowait
Show the percentage of time that the CPU or CPUs were idle during which the
system had an outstanding disk I/O request.
%steal
Show the percentage of time spent in involuntary wait by the virtual CPU or
CPUs while the hypervisor was servicing another virtual processor.
%idle
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 for which statistics are to be displayed may be entered on the com-
mand line. Partitions may also be entered on the command line providing that option
-x is not used. If no device nor partition is entered, then statistics are dis-
played 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 statis-
tics are displayed for every device defined by the system, including those that
have never been used. The report may show the following fields, depending on the
flags used:
Device:
This column gives the device (or partition) name, which is displayed as
hdiskn with 2.2 kernels, for the nth device. It is displayed as devm-n with
2.4 kernels, where m is the major number of the device, and n a distinctive
number. With newer kernels, 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 indeter-
minate size.
Blk_read/s
Indicate the amount of data read from the device expressed in a number of
blocks per second. Blocks are equivalent to sectors with kernels 2.4 and
later 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 device 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 device expressed in kilobytes per
second.
kB_wrtn/s
Indicate the amount of data written to the device expressed in kilobytes per
second.
kB_read
The total number of kilobytes read.
kB_wrtn
The total number of kilobytes written.
MB_read/s
Indicate the amount of data read from the device expressed in megabytes per
second.
MB_wrtn/s
Indicate the amount of data written to the device expressed in megabytes per
second.
MB_read
The total number of megabytes read.
MB_wrtn
The total number of 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 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.
rMB/s
The number of megabytes read from the device per second.
wMB/s
The number of 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.
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
(bandwidth utilization for the device). Device saturation occurs when this
value is close to 100%.
Network Filesystem report
The Network Filesystem (NFS) report provides statistics for each mounted network
filesystem. The report shows the following fields:
Filesystem:
This columns shows the hostname of the NFS server followed by a colon and by
the directory name where the network filesystem is mounted.
rBlk_nor/s
Indicate the number of blocks read by applications via the read(2) system
call interface. A block has a size of 512 bytes.
wBlk_nor/s
Indicate the number of blocks written by applications via the write(2) sys-
tem call interface.
rBlk_dir/s
Indicate the number of blocks read from files opened with the O_DIRECT flag.
wBlk_dir/s
Indicate the number of blocks written to files opened with the O_DIRECT
flag.
rBlk_svr/s
Indicate the number of blocks read from the server by the NFS client via an
NFS READ request.
wBlk_svr/s
Indicate the number of blocks written to the server by the NFS client via an
NFS WRITE request.
rkB_nor/s
Indicate the number of kilobytes read by applications via the read(2) system
call interface.
wkB_nor/s
Indicate the number of kilobytes written by applications via the write(2)
system call interface.
rkB_dir/s
Indicate the number of kilobytes read from files opened with the O_DIRECT
flag.
wkB_dir/s
Indicate the number of kilobytes written to files opened with the O_DIRECT
flag.
rkB_svr/s
Indicate the number of kilobytes read from the server by the NFS client via
an NFS READ request.
wkB_svr/s
Indicate the number of kilobytes written to the server by the NFS client via
an NFS WRITE request.
rMB_nor/s
Indicate the number of megabytes read by applications via the read(2) system
call interface.
wMB_nor/s
Indicate the number of megabytes written by applications via the write(2)
system call interface.
rMB_dir/s
Indicate the number of megabytes read from files opened with the O_DIRECT
flag.
wMB_dir/s
Indicate the number of megabytes written to files opened with the O_DIRECT
flag.
rMB_svr/s
Indicate the number of megabytes read from the server by the NFS client via
an NFS READ request.
wMB_svr/s
Indicate the number of megabytes written to the server by the NFS client via
an NFS WRITE request.
rops/s
Indicate the number of read operations that were issued to the filesystem
per second.
wops/s
Indicate the number of write operations that were issued to the filesystem
per second.
OPTIONS
-c Display the CPU utilization report.
-d Display the device utilization report.
-h Make the NFS report displayed by option -n easier to read by a human.
-k Display statistics in kilobytes per second instead of blocks per second. Data dis-
played are valid only with kernels 2.4 and later.
-m Display statistics in megabytes per second instead of blocks or kilobytes per sec-
ond. Data displayed are valid only with kernels 2.4 and later.
-N Display the registered device mapper names for any device mapper devices. Useful
for viewing LVM2 statistics.
-n Display the network filesystem (NFS) report. This option works only with kernel
2.6.17 and later.
-p [ { device | ALL } ]
The -p option is exclusive of the -x option and 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 dis-
played. 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. Note that this option works only with post 2.5 kernels.
-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. This option is exclusive of the -p one, and works
with post 2.5 kernels since it needs /proc/diskstats file or a mounted sysfs to get
the statistics. This option may also work with older kernels (e.g. 2.4) only if
extended statistics are available in /proc/partitions (the kernel needs to be
patched for that).
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 8601 format (YYYY-MM-DD) instead. The timestamp displayed with option -t
will also be compliant with ISO 8601 format.
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.
iostat -x hda hdb 2 6
Display six reports of extended statistics at two second intervals for devices hda
and hdb.
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.
Extended statistics are available only with post 2.5 kernels.
FILES
/proc/stat contains system statistics.
/proc/uptime contains system uptime.
/proc/partitions contains disk statistics (for pre 2.5 kernels that have been patched).
/proc/diskstats contains disks statistics (for post 2.5 kernels).
/sys contains statistics for block devices (post 2.5 kernels).
/proc/self/mountstats contains statistics for network filesystems.
AUTHOR
Sebastien Godard (sysstat <at> orange.fr)
SEE ALSO
sar(1), pidstat(1), mpstat(1), vmstat(8)
http://pagesperso-orange.fr/sebastien.godard/
Linux MARCH 2008 IOSTAT(1)
Generated by $Id: phpMan.php,v 4.49 2006/02/26 13:18:18 chedong Exp $ Author: Che Dong
On Apache
Under GNU General Public License
2012-05-26 00:34 @38.107.179.238 Crawled by CCBot/1.0 (+http://www.commoncrawl.org/bot.html)