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.TH IOSTATS 4
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.SH NAME
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iostats \- file system to measure I/O
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.SH SYNOPSIS
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.B iostats
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[
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.B -d
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]
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[
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.B -f
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.I dbfile
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]
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.I cmd
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[
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.I args...
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]
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.SH DESCRIPTION
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.I Iostats
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is a user-level file server that interposes itself between a program
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and the regular file server, which
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allows it to gather statistics of file system
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use at the level of the Plan 9 file system protocol, 9P.
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After a program
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exits a report is printed on standard error.
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.PP
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The report consists of three sections.
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The first section reports the amount
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of user data in
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.B read
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and
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.B write
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messages sent by the program and the average rate at
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which the data was transferred.
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The
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.B protocol
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line reports the amount
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of data sent as message headers, that is,
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protocol overhead.
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The
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.B rpc
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line reports the
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total number of file system transactions.
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.PP
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The second section gives
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the number of messages, the fastest, slowest, and average turn around
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time and the amount of data involved with each 9P
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message type.
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The final section gives an I/O summary for each file used
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by the program in terms of opens, reads and writes.
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.PP
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If the
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.B -d
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flag is present, a debugging log including all traffic
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is written to
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.I dbfile
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(default
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.BR iostats.out ).
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.SH EXAMPLE
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Display summary of file I/O incurred by
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.IR ls (1):
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.IP
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.EX
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iostats ls
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.EE
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.PP
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Start a new shell, displaying all 9P traffic caused by the shell or its children:
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.IP
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.EX
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iostats -df /fd/1 rc
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.EE
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.SH SOURCE
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.B /sys/src/cmd/iostats
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.SH SEE ALSO
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.IR dup (3)
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.SH BUGS
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Poor clock resolution means that large amounts of I/O must be done to
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get accurate rate figures.
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.PP
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Can be fooled by programs that do fresh mounts outside its purview,
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or by the use of names of files with content that can vary by process (e.g.,
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.LR #d ,
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.LR /dev/cons ).