| 1 | .\" Copyright (c) 1980 Regents of the University of California. |
| 2 | .\" All rights reserved. The Berkeley software License Agreement |
| 3 | .\" specifies the terms and conditions for redistribution. |
| 4 | .\" |
| 5 | .\" @(#)iostat.8 6.1 (Berkeley) %G% |
| 6 | .\" |
| 7 | .TH IOSTAT 1 "" |
| 8 | .UC 4 |
| 9 | .SH NAME |
| 10 | iostat \- report I/O statistics |
| 11 | .SH SYNOPSIS |
| 12 | .B iostat |
| 13 | [ drives ] |
| 14 | [ interval [ count ] ] |
| 15 | .SH DESCRIPTION |
| 16 | .I Iostat |
| 17 | iteratively reports the number of characters read and written to terminals |
| 18 | per second, |
| 19 | and, for each disk, the number of transfers per second, kilobytes |
| 20 | transferred per second, |
| 21 | and the milliseconds per average seek. |
| 22 | It also gives the percentage of time the system has |
| 23 | spent in user mode, in user mode running low priority (niced) processes, |
| 24 | in system mode, and idling. |
| 25 | .PP |
| 26 | To compute this information, for each disk, seeks and data transfer completions |
| 27 | and number of words transferred are counted; |
| 28 | for terminals collectively, the number |
| 29 | of input and output characters are counted. |
| 30 | Also, each sixtieth of a second, |
| 31 | the state of each disk is examined |
| 32 | and a tally is made if the disk is active. |
| 33 | From these numbers and given the transfer rates |
| 34 | of the devices it is possible to determine |
| 35 | average seek times for each device. |
| 36 | .PP |
| 37 | The optional |
| 38 | .I interval |
| 39 | argument causes |
| 40 | .I iostat |
| 41 | to report once each |
| 42 | .I interval |
| 43 | seconds. |
| 44 | The first report is for all time since a reboot and each |
| 45 | subsequent report is for the last interval only. |
| 46 | .PP |
| 47 | The optional |
| 48 | .I count |
| 49 | argument restricts the number of reports. |
| 50 | .PP |
| 51 | If more than 4 disk drives are configured in the system, |
| 52 | .I iostat |
| 53 | displays only the first 4 drives, with priority given |
| 54 | to Massbus disk drives (i.e. if both Unibus and Massbus |
| 55 | drives are present and the total number of drives exceeds |
| 56 | 4, then some number of Unibus drives will not be displayed |
| 57 | in favor of the Massbus drives). To force |
| 58 | .I iostat |
| 59 | to display specific drives, their names may be supplied on |
| 60 | the command line. |
| 61 | .SH FILES |
| 62 | /dev/kmem |
| 63 | .br |
| 64 | /vmunix |
| 65 | .SH SEE ALSO |
| 66 | vmstat(1) |