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 ] [ -k | -m ] [ -t ] [ -V ] [ -x ] [ device [
11 ... ] | ALL ] [ -p [ device | ALL ] ] [ interval [ count ] ]
12
14 The iostat command is used for monitoring system input/output device
15 loading by observing the time the devices are active in relation to
16 their average transfer rates. The iostat command generates reports that
17 can be used to change system configuration to better balance the
18 input/output load between physical disks.
19 The first report generated by the iostat command provides statistics
21 concerning the time since the system was booted. Each subsequent report
22 covers the time since the previous report. All statistics are reported
23 each time the iostat command is run. The report consists of a CPU
24 header row followed by a row of CPU statistics. On multiprocessor sys‐
25 tems, CPU statistics are calculated system-wide as averages among all
26 processors. A device header row is displayed followed by a line of sta‐
27 tistics for each device that is configured. When option -n is used, an
28 NFS header row is displayed followed by a line of statistics for each
29 network filesystem that is mounted.
30 The interval parameter specifies the amount of time in seconds between
32 each report. The first report contains statistics for the time since
33 system startup (boot). Each subsequent report contains statistics col‐
34 lected during the interval since the previous report. The count parame‐
35 ter can be specified in conjunction with the interval parameter. If the
36 count parameter is specified, the value of count determines the number
37 of reports generated at interval seconds apart. If the interval parame‐
38 ter is specified without the count parameter, the iostat command gener‐
39 ates reports continuously.
40
43 The iostat command generates three types of reports, the CPU Utiliza‐
44 tion report, the Device Utilization report and the Network Filesystem
45 report.
46 CPU Utilization Report
48 The first report generated by the iostat command is the CPU Uti‐
49 lization Report. For multiprocessor systems, the CPU values are
50 global averages among all processors. The report has the fol‐
51 lowing format:
52 %user
54 Show the percentage of CPU utilization that occurred
55 while executing at the user level (application).
56 %nice
57 Show the percentage of CPU utilization that occurred
58 while executing at the user level with nice priority.
59 %system
60 Show the percentage of CPU utilization that occurred
61 while executing at the system level (kernel).
62 %iowait
63 Show the percentage of time that the CPU or CPUs were
64 idle during which the system had an outstanding disk I/O
65 request.
66 %steal
67 Show the percentage of time spent in involuntary wait by
68 the virtual CPU or CPUs while the hypervisor was servic‐
69 ing another virtual processor.
70 %idle
71 Show the percentage of time that the CPU or CPUs were
72 idle and the system did not have an outstanding disk I/O
73 request.
74 Device Utilization Report
76 The second report generated by the iostat command is the Device
77 Utilization Report. The device report provides statistics on a
78 per physical device or partition basis. Block devices for which
79 statistics are to be displayed may be entered on the command
80 line. Partitions may also be entered on the command line provid‐
81 ing that option -x is not used. If no device nor partition is
82 entered, then statistics are displayed for every device used by
83 the system, and providing that the kernel maintains statistics
84 for it. If the ALL keyword is given on the command line, then
85 statistics are displayed for every device defined by the system,
86 including those that have never been used. The report may show
87 the following fields, depending on the flags used:
88 Device:
90 This column gives the device (or partition) name, which
91 is displayed as hdiskn with 2.2 kernels, for the nth
92 device. It is displayed as devm-n with 2.4 kernels, where
93 m is the major number of the device, and n a distinctive
94 number. With newer kernels, the device name as listed in
95 the /dev directory is displayed.
96 tps
98 Indicate the number of transfers per second that were
99 issued to the device. A transfer is an I/O request to the
100 device. Multiple logical requests can be combined into a
101 single I/O request to the device. A transfer is of inde‐
102 terminate size.
103 Blk_read/s
105 Indicate the amount of data read from the device
106 expressed in a number of blocks per second. Blocks are
107 equivalent to sectors with kernels 2.4 and later and
108 therefore have a size of 512 bytes. With older kernels, a
109 block is of indeterminate size.
110 Blk_wrtn/s
112 Indicate the amount of data written to the device
113 expressed in a number of blocks per second.
114 Blk_read
116 The total number of blocks read.
117 Blk_wrtn
119 The total number of blocks written.
120 kB_read/s
122 Indicate the amount of data read from the device
123 expressed in kilobytes per second.
124 kB_wrtn/s
126 Indicate the amount of data written to the device
127 expressed in kilobytes per second.
128 kB_read
130 The total number of kilobytes read.
131 kB_wrtn
133 The total number of kilobytes written.
134 MB_read/s
136 Indicate the amount of data read from the device
137 expressed in megabytes per second.
138 MB_wrtn/s
140 Indicate the amount of data written to the device
141 expressed in megabytes per second.
142 MB_read
144 The total number of megabytes read.
145 MB_wrtn
147 The total number of megabytes written.
148 rrqm/s
150 The number of read requests merged per second that were
151 queued to the device.
152 wrqm/s
154 The number of write requests merged per second that were
155 queued to the device.
156 r/s
158 The number of read requests that were issued to the
159 device per second.
160 w/s
162 The number of write requests that were issued to the
163 device per second.
164 rsec/s
166 The number of sectors read from the device per second.
167 wsec/s
169 The number of sectors written to the device per second.
170 rkB/s
172 The number of kilobytes read from the device per second.
173 wkB/s
175 The number of kilobytes written to the device per second.
176 rMB/s
178 The number of megabytes read from the device per second.
179 wMB/s
181 The number of megabytes written to the device per second.
182 avgrq-sz
184 The average size (in sectors) of the requests that were
185 issued to the device.
186 avgqu-sz
188 The average queue length of the requests that were issued
189 to the device.
190 await
192 The average time (in milliseconds) for I/O requests
193 issued to the device to be served. This includes the time
194 spent by the requests in queue and the time spent servic‐
195 ing them.
196 svctm
198 The average service time (in milliseconds) for I/O
199 requests that were issued to the device.
200 %util
202 Percentage of CPU time during which I/O requests were
203 issued to the device (bandwidth utilization for the
204 device). Device saturation occurs when this value is
205 close to 100%.
206 Network Filesystem report
208 The Network Filesystem (NFS) report provides statistics for each
209 mounted network filesystem. The report shows the following
210 fields:
211 Filesystem:
213 This columns shows the hostname of the NFS server fol‐
214 lowed by a colon and by the directory name where the net‐
215 work filesystem is mounted.
216 rBlk_nor/s
218 Indicate the number of blocks read by applications via
219 the read(2) system call interface. A block has a size of
220 512 bytes.
221 wBlk_nor/s
223 Indicate the number of blocks written by applications via
224 the write(2) system call interface.
225 rBlk_dir/s
227 Indicate the number of blocks read from files opened with
228 the O_DIRECT flag.
229 wBlk_dir/s
231 Indicate the number of blocks written to files opened
232 with the O_DIRECT flag.
233 rBlk_svr/s
235 Indicate the number of blocks read from the server by the
236 NFS client via an NFS READ request.
237 wBlk_svr/s
239 Indicate the number of blocks written to the server by
240 the NFS client via an NFS WRITE request.
241 rkB_nor/s
243 Indicate the number of kilobytes read by applications via
244 the read(2) system call interface.
245 wkB_nor/s
247 Indicate the number of kilobytes written by applications
248 via the write(2) system call interface.
249 rkB_dir/s
251 Indicate the number of kilobytes read from files opened
252 with the O_DIRECT flag.
253 wkB_dir/s
255 Indicate the number of kilobytes written to files opened
256 with the O_DIRECT flag.
257 rkB_svr/s
259 Indicate the number of kilobytes read from the server by
260 the NFS client via an NFS READ request.
261 wkB_svr/s
263 Indicate the number of kilobytes written to the server by
264 the NFS client via an NFS WRITE request.
265 rMB_nor/s
267 Indicate the number of megabytes read by applications via
268 the read(2) system call interface.
269 wMB_nor/s
271 Indicate the number of megabytes written by applications
272 via the write(2) system call interface.
273 rMB_dir/s
275 Indicate the number of megabytes read from files opened
276 with the O_DIRECT flag.
277 wMB_dir/s
279 Indicate the number of megabytes written to files opened
280 with the O_DIRECT flag.
281 rMB_svr/s
283 Indicate the number of megabytes read from the server by
284 the NFS client via an NFS READ request.
285 wMB_svr/s
287 Indicate the number of megabytes written to the server by
288 the NFS client via an NFS WRITE request.
289
291 -c Display the CPU utilization report.
292 -d Display the device utilization report.
294 -k Display statistics in kilobytes per second instead of blocks per
296 second. Data displayed are valid only with kernels 2.4 and
297 later.
298 -m Display statistics in megabytes per second instead of blocks or
300 kilobytes per second. Data displayed are valid only with ker‐
301 nels 2.4 and later.
302 -n Display the network filesystem (NFS) report. This option works
304 only with kernel 2.6.17 and later.
305 -p [ { device | ALL } ]
307 The -p option is exclusive of the -x option and displays statis‐
308 tics for block devices and all their partitions that are used by
309 the system. If a device name is entered on the command line,
310 then statistics for it and all its partitions are displayed.
311 Last, the ALL keyword indicates that statistics have to be dis‐
312 played for all the block devices and partitions defined by the
313 system, including those that have never been used. Note that
314 this option works only with post 2.5 kernels.
315 -t Print the time for each report displayed.
317 -V Print version number then exit.
319 -x Display extended statistics. This option is exclusive of the -p
321 one, and works with post 2.5 kernels since it needs
322 /proc/diskstats file or a mounted sysfs to get the statistics.
323 This option may also work with older kernels (e.g. 2.4) only if
324 extended statistics are available in /proc/partitions (the ker‐
325 nel needs to be patched for that).
326
329 The iostat command takes into account the following environment vari‐
330 able:
331 S_TIME_FORMAT
334 If this variable exists and its value is ISO then the current
335 locale will be ignored when printing the date in the report
336 header. The iostat command will use the ISO 8601 format (YYYY-
337 MM-DD) instead.
338
341 iostat
342 Display a single history since boot report for all CPU and
343 Devices.
344 iostat -d 2
346 Display a continuous device report at two second intervals.
347 iostat -d 2 6
349 Display six reports at two second intervals for all devices.
350 iostat -x hda hdb 2 6
352 Display six reports of extended statistics at two second inter‐
353 vals for devices hda and hdb.
354 iostat -p sda 2 6
356 Display six reports at two second intervals for device sda and
357 all its partitions (sda1, etc.)
358
360 /proc filesystem must be mounted for iostat to work.
361 On SMP machines iostat assumes that CPU #0 is never disabled. Indeed
363 iostat uses it to calculate the time interval.
364 Extended statistics are available only with post 2.5 kernels.
366
368 /proc/stat contains system statistics.
369 /proc/partitions contains disk statistics (for pre 2.5 kernels that
371 have been patched).
372 /proc/diskstats contains disks statistics (for post 2.5 kernels).
374 /sys contains statistics for block devices (post 2.5 kernels).
376 /proc/self/mountstats contains statistics for network filesystems.
378
380 Sebastien Godard (sysstat <at> wanadoo.fr)
381
383 sar(1), mpstat(1), vmstat(8)
384 http://perso.orange.fr/sebastien.godard/
386Linux JANUARY 2007 IOSTAT(1)