.TH IOSTAT 1M .SH NAME iostat \- report I/O statistics .SH SYNOPSIS .B iostat [ option ] ... [ drive ] ... [ interval [ count ] ] .SH DESCRIPTION .I Iostat delves into the system and reports certain statistics kept about input-output activity. Information is kept about up to six different disks (HP, HM, HK, ML, RP, RL) and about typewriters. For each disk drive, I/O completions and number of words transferred are counted; for typewriters collectively, the number of input and output characters are counted. Also, each sixtieth of a second, the state of each disk drive is examined and a tally is made if the disk drive is active. The processor state is also examined, this tally goes into one of four categories, depending on whether the system is executing in user mode, in `nice' (background) user mode, in system mode, or idle. The .I iostat reports are for all types of activity, seeks as well as data transfers, on all drives that have had any I/O activity since the system was booted, inactive and nonexistent drives are ignored. .PP The optional .I drive argument allows the reports to be limited to a specified subset of the available drives. Up to six drive names, of the form; hp0, ml1, rl3, rp4, etc., may be specified. Reports will be generated for only those drives which exist and have been active. .PP The optional .I interval argument causes .I iostat to report once each .I interval seconds. The first report is for all time since a reboot and each subsequent report is for the last interval only. .PP The optional .I count argument restricts the number of reports. .PP With no option argument .I iostat reports for each disk the number of transfers per minute, the milliseconds per average seek, and the milliseconds per data transfer exclusive of seek time. It also gives the percentage of time the system has spend in each of the four categories mentioned above. .PP The following options are available: .TP .B \-t Report the number of characters of terminal IO per second as well. .TP .B \-i Report the percentage of time spend in each of the four categories mentioned above, the percentage of time each disk controller was active (seeking or transferring, the percentage of time any diks drive was active, and the percentage of time spent in `IO wait:' idle, but with a disk drive active. .TP .B \-s Report the raw timing information for each active disk drive. The information consists of; the disk controller name and drive number, the disk's transfer rate (microseconds/word), the percentage of the total system time that the drive had I/O activity, the number of transfers on that drive, and the number of words transferred by the drive. .TP .B \-b Report on the usage of I/O buffers. The report gives; the number of buffers in the pool, the number of buffered reads, number of read-ahead blocks, number of buffer cache hits, number of buffered writes, and the number of I/O operations on each buffer starting with the first one. .TP .B \-d Print the date and time at the head of the report. .TP .B \-a Print the total time in minutes at the end of the report. .SH FILES /dev/mem, /unix .SH BUGS The accuracy of the .I iostat reports is subject to the sixtieth of a second granularity of the system clock.