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 and partitions.
8
10 iostat [ -c ] [ -d ] [ -h ] [ -k | -m ] [ -N ] [ -s ] [ -t ] [ -V ] [
11 -x ] [ -y ] [ -z ] [ -j { ID | LABEL | PATH | UUID | ... } ] [ -o JSON
12 ] [ [ -H ] -g group_name ] [ --human ] [ -p [ device [,...] | ALL ] ] [
13 device [...] | ALL ] [ interval [ count ] ]
14
16 The iostat command is used for monitoring system input/output device
17 loading by observing the time the devices are active in relation to
18 their average transfer rates. The iostat command generates reports that
19 can be used to change system configuration to better balance the
20 input/output load between physical disks.
21 The first report generated by the iostat command provides statistics
23 concerning the time since the system was booted, unless the -y option
24 is used (in this case, this first report is omitted). Each subsequent
25 report covers the time since the previous report. All statistics are
26 reported each time the iostat command is run. The report consists of a
27 CPU header row followed by a row of CPU statistics. On multiprocessor
28 systems, CPU statistics are calculated system-wide as averages among
29 all processors. A device header row is displayed followed by a line of
30 statistics for each device that is configured.
31 The interval parameter specifies the amount of time in seconds between
33 each report. The count parameter can be specified in conjunction with
34 the interval parameter. If the count parameter is specified, the value
35 of count determines the number of reports generated at interval seconds
36 apart. If the interval parameter is specified without the count parame‐
37 ter, the iostat command generates reports continuously.
38
41 The iostat command generates two types of reports, the CPU Utilization
42 report and the Device Utilization report.
43 CPU Utilization Report
45 The first report generated by the iostat command is the CPU Uti‐
46 lization Report. For multiprocessor systems, the CPU values are
47 global averages among all processors. The report has the fol‐
48 lowing format:
49 %user
51 Show the percentage of CPU utilization that occurred
52 while executing at the user level (application).
53 %nice
55 Show the percentage of CPU utilization that occurred
56 while executing at the user level with nice priority.
57 %system
59 Show the percentage of CPU utilization that occurred
60 while executing at the system level (kernel).
61 %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
68 Show the percentage of time spent in involuntary wait by
69 the virtual CPU or CPUs while the hypervisor was servic‐
70 ing another virtual processor.
71 %idle
73 Show the percentage of time that the CPU or CPUs were
74 idle and the system did not have an outstanding disk I/O
75 request.
76 Device Utilization Report
78 The second report generated by the iostat command is the Device
79 Utilization Report. The device report provides statistics on a
80 per physical device or partition basis. Block devices and parti‐
81 tions for which statistics are to be displayed may be entered on
82 the command line. If no device nor partition is entered, then
83 statistics are displayed for every device used by the system,
84 and providing that the kernel maintains statistics for it. If
85 the ALL keyword is given on the command line, then statistics
86 are displayed for every device defined by the system, including
87 those that have never been used. Transfer rates are shown in 1K
88 blocks by default, unless the environment variable POSIXLY_COR‐
89 RECT is set, in which case 512-byte blocks are used. The report
90 may show the following fields, depending on the flags used:
91 Device:
93 This column gives the device (or partition) name as
94 listed in the /dev directory.
95 tps
97 Indicate the number of transfers per second that were
98 issued to the device. A transfer is an I/O request to the
99 device. Multiple logical requests can be combined into a
100 single I/O request to the device. A transfer is of inde‐
101 terminate size.
102 Blk_read/s (kB_read/s, MB_read/s)
104 Indicate the amount of data read from the device
105 expressed in a number of blocks (kilobytes, megabytes)
106 per second. Blocks are equivalent to sectors and there‐
107 fore have a size of 512 bytes.
108 Blk_wrtn/s (kB_wrtn/s, MB_wrtn/s)
110 Indicate the amount of data written to the device
111 expressed in a number of blocks (kilobytes, megabytes)
112 per second.
113 Blk_read (kB_read, MB_read)
115 The total number of blocks (kilobytes, megabytes) read.
116 Blk_wrtn (kB_wrtn, MB_wrtn)
118 The total number of blocks (kilobytes, megabytes) writ‐
119 ten.
120 r/s
122 The number (after merges) of read requests completed per
123 second for the device.
124 w/s
126 The number (after merges) of write requests completed per
127 second for the device.
128 sec/s (kB/s, MB/s)
130 The number of sectors (kilobytes, megabytes) read from or
131 written to the device per second.
132 rsec/s (rkB/s, rMB/s)
134 The number of sectors (kilobytes, megabytes) read from
135 the device per second.
136 wsec/s (wkB/s, wMB/s)
138 The number of sectors (kilobytes, megabytes) written to
139 the device per second.
140 rqm/s
142 The number of I/O requests merged per second that were
143 queued to the device.
144 rrqm/s
146 The number of read requests merged per second that were
147 queued to the device.
148 wrqm/s
150 The number of write requests merged per second that were
151 queued to the device.
152 %rrqm
154 The percentage of read requests merged together before
155 being sent to the device.
156 %wrqm
158 The percentage of write requests merged together before
159 being sent to the device.
160 areq-sz
162 The average size (in kilobytes) of the I/O requests that
163 were issued to the device.
164 Note: In previous versions, this field was known as
165 avgrq-sz and was expressed in sectors.
166 rareq-sz
168 The average size (in kilobytes) of the read requests that
169 were issued to the device.
170 wareq-sz
172 The average size (in kilobytes) of the write requests
173 that were issued to the device.
174 await
176 The average time (in milliseconds) for I/O requests
177 issued to the device to be served. This includes the time
178 spent by the requests in queue and the time spent servic‐
179 ing them.
180 r_await
182 The average time (in milliseconds) for read requests
183 issued to the device to be served. This includes the time
184 spent by the requests in queue and the time spent servic‐
185 ing them.
186 w_await
188 The average time (in milliseconds) for write requests
189 issued to the device to be served. This includes the time
190 spent by the requests in queue and the time spent servic‐
191 ing them.
192 aqu-sz
194 The average queue length of the requests that were issued
195 to the device.
196 Note: In previous versions, this field was known as
197 avgqu-sz.
198 svctm
200 The average service time (in milliseconds) for I/O
201 requests that were issued to the device. Warning! Do not
202 trust this field any more. This field will be removed in
203 a future sysstat version.
204 %util
206 Percentage of elapsed time during which I/O requests were
207 issued to the device (bandwidth utilization for the
208 device). Device saturation occurs when this value is
209 close to 100% for devices serving requests serially. But
210 for devices serving requests in parallel, such as RAID
211 arrays and modern SSDs, this number does not reflect
212 their performance limits.
213
215 -c Display the CPU utilization report.
216 -d Display the device utilization report.
218 -g group_name { device [...] | ALL }
220 Display statistics for a group of devices. The iostat command
221 reports statistics for each individual device in the list then a
222 line of global statistics for the group displayed as group_name
223 and made up of all the devices in the list. The ALL keyword
224 means that all the block devices defined by the system shall be
225 included in the group.
226 -H This option must be used with option -g and indicates that only
228 global statistics for the group are to be displayed, and not
229 statistics for individual devices in the group.
230 -h Make the Device Utilization Report easier to read by a human.
232 --human is enabled implicitly with this option.
233 --human
235 Print sizes in human readable format (e.g. 1.0k, 1.2M, etc.)
236 The units displayed with this option supersede any other default
237 units (e.g. kilobytes, sectors...) associated with the metrics.
238 -j { ID | LABEL | PATH | UUID | ... } [ device [...] | ALL ]
240 Display persistent device names. Options ID, LABEL, etc. specify
241 the type of the persistent name. These options are not limited,
242 only prerequisite is that directory with required persistent
243 names is present in /dev/disk. Optionally, multiple devices can
244 be specified in the chosen persistent name type. Because per‐
245 sistent device names are usually long, option
246 -k Display statistics in kilobytes per second.
248 -m Display statistics in megabytes per second.
250 -N Display the registered device mapper names for any device mapper
252 devices. Useful for viewing LVM2 statistics.
253 -o JSON
255 Display the statistics in JSON (Javascript Object Notation) for‐
256 mat. JSON output field order is undefined, and new fields may
257 be added in the future.
258 -p [ { device [,...] | ALL } ]
260 The -p option displays statistics for block devices and all
261 their partitions that are used by the system. If a device name
262 is entered on the command line, then statistics for it and all
263 its partitions are displayed. Last, the ALL keyword indicates
264 that statistics have to be displayed for all the block devices
265 and partitions defined by the system, including those that have
266 never been used. If option -j is defined before this option,
267 devices entered on the command line can be specified with the
268 chosen persistent name type.
269 -s Display a short (narrow) version of the report that should fit
271 in 80 characters wide screens.
272 -t Print the time for each report displayed. The timestamp format
274 may depend on the value of the S_TIME_FORMAT environment vari‐
275 able (see below).
276 -V Print version number then exit.
278 -x Display extended statistics.
280 -y Omit first report with statistics since system boot, if display‐
282 ing multiple records at given interval.
283 -z Tell iostat to omit output for any devices for which there was
285 no activity during the sample period.
286
289 The iostat command takes into account the following environment vari‐
290 ables:
291 POSIXLY_CORRECT
294 When this variable is set, transfer rates are shown in 512-byte
295 blocks instead of the default 1K blocks.
296 S_COLORS
299 When this variable is set, display statistics in color on the
300 terminal. Possible values for this variable are never, always
301 or auto (the latter is the default).
302 Please note that the color (being red, yellow, or some other
304 color) used to display a value is not indicative of any kind of
305 issue simply because of the color. It only indicates different
306 ranges of values.
307 S_COLORS_SGR
310 Specify the colors and other attributes used to display statis‐
311 tics on the terminal. Its value is a colon-separated list of
312 capabilities that defaults to
313 H=31;1:I=32;22:M=35;1:N=34;1:Z=34;22. Supported capabilities
314 are:
315 H= SGR (Select Graphic Rendition) substring for percentage
318 values greater than or equal to 75%.
319 I= SGR substring for device names.
322 M= SGR substring for percentage values in the range from 50%
325 to 75%.
326 N= SGR substring for non-zero statistics values.
329 Z= SGR substring for zero values.
332 S_TIME_FORMAT
335 If this variable exists and its value is ISO then the current
336 locale will be ignored when printing the date in the report
337 header. The iostat command will use the ISO 8601 format (YYYY-
338 MM-DD) instead. The timestamp displayed with option -t will
339 also be compliant with ISO 8601 format.
340
343 iostat
344 Display a single history since boot report for all CPU and
345 Devices.
346 iostat -d 2
348 Display a continuous device report at two second intervals.
349 iostat -d 2 6
351 Display six reports at two second intervals for all devices.
352 iostat -x sda sdb 2 6
354 Display six reports of extended statistics at two second inter‐
355 vals for devices sda and sdb.
356 iostat -p sda 2 6
358 Display six reports at two second intervals for device sda and
359 all its partitions (sda1, etc.)
360
362 /proc filesystem must be mounted for iostat to work.
363 Kernels older than 2.6.x are no longer supported.
365 The average service time (svctm field) value is meaningless, as I/O
367 statistics are now calculated at block level, and we don't know when
368 the disk driver starts to process a request. For this reason, this
369 field will be removed in a future sysstat version.
370
372 /proc/stat contains system statistics.
373 /proc/uptime contains system uptime.
375 /proc/diskstats contains disks statistics.
377 /sys contains statistics for block devices.
379 /proc/self/mountstats contains statistics for network filesystems.
381 /dev/disk contains persistent device names.
383
385 Sebastien Godard (sysstat <at> orange.fr)
386
388 sar(1), pidstat(1), mpstat(1), vmstat(8), tapestat(1), nfsiostat(1),
389 cifsiostat(1)
390 http://pagesperso-orange.fr/sebastien.godard/
392Linux JANUARY 2018 IOSTAT(1)