1IOSTAT(1) Linux User's Manual IOSTAT(1)
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6 iostat - Report Central Processing Unit (CPU) statistics and input/out‐
7 put statistics for devices, partitions and network filesystems (NFS).
8
10 iostat [ -c ] [ -d ] [ -N ] [ -n ] [ -h ] [ -k | -m ] [ -t ] [ -V ] [
11 -x ] [ -z ] [ device [...] | ALL ] [ -p [ device [,...] | ALL ] ] [
12 interval [ count ] ]
13
15 The iostat command is used for monitoring system input/output device
16 loading by observing the time the devices are active in relation to
17 their average transfer rates. The iostat command generates reports that
18 can be used to change system configuration to better balance the
19 input/output load between physical disks.
20 The first report generated by the iostat command provides statistics
22 concerning the time since the system was booted. Each subsequent report
23 covers the time since the previous report. All statistics are reported
24 each time the iostat command is run. The report consists of a CPU
25 header row followed by a row of CPU statistics. On multiprocessor sys‐
26 tems, CPU statistics are calculated system-wide as averages among all
27 processors. A device header row is displayed followed by a line of sta‐
28 tistics for each device that is configured. When option -n is used, an
29 NFS header row is displayed followed by a line of statistics for each
30 network filesystem that is mounted.
31 The interval parameter specifies the amount of time in seconds between
33 each report. The first report contains statistics for the time since
34 system startup (boot). Each subsequent report contains statistics col‐
35 lected during the interval since the previous report. The count parame‐
36 ter can be specified in conjunction with the interval parameter. If the
37 count parameter is specified, the value of count determines the number
38 of reports generated at interval seconds apart. If the interval parame‐
39 ter is specified without the count parameter, the iostat command gener‐
40 ates reports continuously.
41
44 The iostat command generates three types of reports, the CPU Utiliza‐
45 tion report, the Device Utilization report and the Network Filesystem
46 report.
47 CPU Utilization Report
49 The first report generated by the iostat command is the CPU Uti‐
50 lization Report. For multiprocessor systems, the CPU values are
51 global averages among all processors. The report has the fol‐
52 lowing format:
53 %user
55 Show the percentage of CPU utilization that occurred
56 while executing at the user level (application).
57 %nice
59 Show the percentage of CPU utilization that occurred
60 while executing at the user level with nice priority.
61 %system
63 Show the percentage of CPU utilization that occurred
64 while executing at the system level (kernel).
65 %iowait
67 Show the percentage of time that the CPU or CPUs were
68 idle during which the system had an outstanding disk I/O
69 request.
70 %steal
72 Show the percentage of time spent in involuntary wait by
73 the virtual CPU or CPUs while the hypervisor was servic‐
74 ing another virtual processor.
75 %idle
77 Show the percentage of time that the CPU or CPUs were
78 idle and the system did not have an outstanding disk I/O
79 request.
80 Device Utilization Report
82 The second report generated by the iostat command is the Device
83 Utilization Report. The device report provides statistics on a
84 per physical device or partition basis. Block devices and parti‐
85 tions for which statistics are to be displayed may be entered on
86 the command line. If no device nor partition is entered, then
87 statistics are displayed for every device used by the system,
88 and providing that the kernel maintains statistics for it. If
89 the ALL keyword is given on the command line, then statistics
90 are displayed for every device defined by the system, including
91 those that have never been used. The report may show the fol‐
92 lowing fields, depending on the flags used:
93 Device:
95 This column gives the device (or partition) name, which
96 is displayed as hdiskn with 2.2 kernels, for the nth
97 device. It is displayed as devm-n with 2.4 kernels, where
98 m is the major number of the device, and n a distinctive
99 number. With newer kernels, the device name as listed in
100 the /dev directory is displayed.
101 tps
103 Indicate the number of transfers per second that were
104 issued to the device. A transfer is an I/O request to the
105 device. Multiple logical requests can be combined into a
106 single I/O request to the device. A transfer is of inde‐
107 terminate size.
108 Blk_read/s
110 Indicate the amount of data read from the device
111 expressed in a number of blocks per second. Blocks are
112 equivalent to sectors with kernels 2.4 and later and
113 therefore have a size of 512 bytes. With older kernels, a
114 block is of indeterminate size.
115 Blk_wrtn/s
117 Indicate the amount of data written to the device
118 expressed in a number of blocks per second.
119 Blk_read
121 The total number of blocks read.
122 Blk_wrtn
124 The total number of blocks written.
125 kB_read/s
127 Indicate the amount of data read from the device
128 expressed in kilobytes per second.
129 kB_wrtn/s
131 Indicate the amount of data written to the device
132 expressed in kilobytes per second.
133 kB_read
135 The total number of kilobytes read.
136 kB_wrtn
138 The total number of kilobytes written.
139 MB_read/s
141 Indicate the amount of data read from the device
142 expressed in megabytes per second.
143 MB_wrtn/s
145 Indicate the amount of data written to the device
146 expressed in megabytes per second.
147 MB_read
149 The total number of megabytes read.
150 MB_wrtn
152 The total number of megabytes written.
153 rrqm/s
155 The number of read requests merged per second that were
156 queued to the device.
157 wrqm/s
159 The number of write requests merged per second that were
160 queued to the device.
161 r/s
163 The number of read requests that were issued to the
164 device per second.
165 w/s
167 The number of write requests that were issued to the
168 device per second.
169 rsec/s
171 The number of sectors read from the device per second.
172 wsec/s
174 The number of sectors written to the device per second.
175 rkB/s
177 The number of kilobytes read from the device per second.
178 wkB/s
180 The number of kilobytes written to the device per second.
181 rMB/s
183 The number of megabytes read from the device per second.
184 wMB/s
186 The number of megabytes written to the device per second.
187 avgrq-sz
189 The average size (in sectors) of the requests that were
190 issued to the device.
191 avgqu-sz
193 The average queue length of the requests that were issued
194 to the device.
195 await
197 The average time (in milliseconds) for I/O requests
198 issued to the device to be served. This includes the time
199 spent by the requests in queue and the time spent servic‐
200 ing them.
201 svctm
203 The average service time (in milliseconds) for I/O
204 requests that were issued to the device.
205 %util
207 Percentage of CPU time during which I/O requests were
208 issued to the device (bandwidth utilization for the
209 device). Device saturation occurs when this value is
210 close to 100%.
211 Network Filesystem report
213 The Network Filesystem (NFS) report provides statistics for each
214 mounted network filesystem. The report shows the following
215 fields:
216 Filesystem:
218 This columns shows the hostname of the NFS server fol‐
219 lowed by a colon and by the directory name where the net‐
220 work filesystem is mounted.
221 rBlk_nor/s
223 Indicate the number of blocks read by applications via
224 the read(2) system call interface. A block has a size of
225 512 bytes.
226 wBlk_nor/s
228 Indicate the number of blocks written by applications via
229 the write(2) system call interface.
230 rBlk_dir/s
232 Indicate the number of blocks read from files opened with
233 the O_DIRECT flag.
234 wBlk_dir/s
236 Indicate the number of blocks written to files opened
237 with the O_DIRECT flag.
238 rBlk_svr/s
240 Indicate the number of blocks read from the server by the
241 NFS client via an NFS READ request.
242 wBlk_svr/s
244 Indicate the number of blocks written to the server by
245 the NFS client via an NFS WRITE request.
246 rkB_nor/s
248 Indicate the number of kilobytes read by applications via
249 the read(2) system call interface.
250 wkB_nor/s
252 Indicate the number of kilobytes written by applications
253 via the write(2) system call interface.
254 rkB_dir/s
256 Indicate the number of kilobytes read from files opened
257 with the O_DIRECT flag.
258 wkB_dir/s
260 Indicate the number of kilobytes written to files opened
261 with the O_DIRECT flag.
262 rkB_svr/s
264 Indicate the number of kilobytes read from the server by
265 the NFS client via an NFS READ request.
266 wkB_svr/s
268 Indicate the number of kilobytes written to the server by
269 the NFS client via an NFS WRITE request.
270 rMB_nor/s
272 Indicate the number of megabytes read by applications via
273 the read(2) system call interface.
274 wMB_nor/s
276 Indicate the number of megabytes written by applications
277 via the write(2) system call interface.
278 rMB_dir/s
280 Indicate the number of megabytes read from files opened
281 with the O_DIRECT flag.
282 wMB_dir/s
284 Indicate the number of megabytes written to files opened
285 with the O_DIRECT flag.
286 rMB_svr/s
288 Indicate the number of megabytes read from the server by
289 the NFS client via an NFS READ request.
290 wMB_svr/s
292 Indicate the number of megabytes written to the server by
293 the NFS client via an NFS WRITE request.
294 ops/s
296 Indicate the number of operations that were issued to the
297 filesystem per second.
298 rops/s
300 Indicate the number of 'read' operations that were issued
301 to the filesystem per second.
302 wops/s
304 Indicate the number of 'write' operations that were
305 issued to the filesystem per second.
306
308 -c Display the CPU utilization report.
309 -d Display the device utilization report.
311 -h Make the NFS report displayed by option -n easier to read by a
313 human.
314 -k Display statistics in kilobytes per second instead of blocks per
316 second. Data displayed are valid only with kernels 2.4 and
317 later.
318 -m Display statistics in megabytes per second instead of blocks or
320 kilobytes per second. Data displayed are valid only with ker‐
321 nels 2.4 and later.
322 -N Display the registered device mapper names for any device mapper
324 devices. Useful for viewing LVM2 statistics.
325 -n Display the network filesystem (NFS) report. This option works
327 only with kernel 2.6.17 and later.
328 -p [ { device [,...] | ALL } ]
330 The -p option displays statistics for block devices and all
331 their partitions that are used by the system. If a device name
332 is entered on the command line, then statistics for it and all
333 its partitions are displayed. Last, the ALL keyword indicates
334 that statistics have to be displayed for all the block devices
335 and partitions defined by the system, including those that have
336 never been used. Note that this option works only with post 2.5
337 kernels.
338 -t Print the time for each report displayed. The timestamp format
340 may depend on the value of the S_TIME_FORMAT environment vari‐
341 able (see below).
342 -V Print version number then exit.
344 -x Display extended statistics. This option works with post 2.5
346 kernels since it needs /proc/diskstats file or a mounted sysfs
347 to get the statistics. This option may also work with older ker‐
348 nels (e.g. 2.4) only if extended statistics are available in
349 /proc/partitions (the kernel needs to be patched for that).
350 -z Tell iostat to omit output for any devices for which there was
352 no activity during the sample period.
353
356 The iostat command takes into account the following environment vari‐
357 able:
358 S_TIME_FORMAT
361 If this variable exists and its value is ISO then the current
362 locale will be ignored when printing the date in the report
363 header. The iostat command will use the ISO 8601 format (YYYY-
364 MM-DD) instead. The timestamp displayed with option -t will
365 also be compliant with ISO 8601 format.
366
369 iostat
370 Display a single history since boot report for all CPU and
371 Devices.
372 iostat -d 2
374 Display a continuous device report at two second intervals.
375 iostat -d 2 6
377 Display six reports at two second intervals for all devices.
378 iostat -x sda sdb 2 6
380 Display six reports of extended statistics at two second inter‐
381 vals for devices sda and sdb.
382 iostat -p sda 2 6
384 Display six reports at two second intervals for device sda and
385 all its partitions (sda1, etc.)
386
388 /proc filesystem must be mounted for iostat to work.
389 Extended statistics are available only with post 2.5 kernels.
391
393 /proc/stat contains system statistics.
394 /proc/uptime contains system uptime.
396 /proc/partitions contains disk statistics (for pre 2.5 kernels that
398 have been patched).
399 /proc/diskstats contains disks statistics (for post 2.5 kernels).
401 /sys contains statistics for block devices (post 2.5 kernels).
403 /proc/self/mountstats contains statistics for network filesystems.
405
407 Sebastien Godard (sysstat <at> orange.fr)
408
410 sar(1), pidstat(1), mpstat(1), vmstat(8)
411 http://pagesperso-orange.fr/sebastien.godard/
413Linux DECEMBER 2009 IOSTAT(1)