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diff -up man-pages-3.53/man5/proc.5.orig man-pages-3.53/man5/proc.5
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--- man-pages-3.53/man5/proc.5.orig 2013-07-31 08:45:56.000000000 +0200
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+++ man-pages-3.53/man5/proc.5 2013-08-02 13:00:55.062278000 +0200
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@@ -59,7 +59,7 @@
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.\" to see what information could be imported from that file
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.\" into this file.
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.\"
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-.TH PROC 5 2013-06-27 "Linux" "Linux Programmer's Manual"
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+.TH PROC 5 2013-08-01 "Linux" "Linux Programmer's Manual"
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.SH NAME
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proc \- process information pseudo-file system
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.SH DESCRIPTION
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@@ -350,9 +350,88 @@ file access mode and file status flags (
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.BR open (2)).
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The files in this directory are readable only by the owner of the process.
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-.\" FIXME document /proc/[pid]/io
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-.\" .TP
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-.\" .IR /proc/[pid]/io " (since kernel 2.6.20)"
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+.TP
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+.IR /proc/[pid]/io " (since kernel 2.6.20)"
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+.\" commit 7c3ab7381e79dfc7db14a67c6f4f3285664e1ec2
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+This file contains I/O statistics for the process, for example:
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+.in +4n
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+.nf
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+
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+.RB "#" " cat /proc/3828/io"
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+rchar: 323934931
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+wchar: 323929600
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+syscr: 632687
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+syscw: 632675
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+read_bytes: 0
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+write_bytes: 323932160
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+cancelled_write_bytes: 0
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+.fi
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+.in
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+
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+The fields are as follows:
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+.RS
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+.TP
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+.IR rchar ": characters read"
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+The number of bytes which this task has caused to be read from storage.
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+This is simply the sum of bytes which this process passed to
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+.BR read (2)
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+and similar system calls.
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+It includes things such as terminal I/O and
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+is unaffected by whether or not actual
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+physical disk I/O was required (the read might have been satisfied from
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+pagecache).
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+.TP
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+.IR wchar ": characters written"
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+The number of bytes which this task has caused, or shall cause to be written
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+to disk.
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+Similar caveats apply here as with
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+.IR rchar .
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+.TP
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+.IR syscr ": read syscalls"
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+Attempt to count the number of read I/O operations\(emthat is,
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+system calls such as
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+.BR read (2)
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+and
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+.BR pread (2).
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+.TP
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+.IR syscw ": write syscalls"
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+Attempt to count the number of write I/O operations\(emthat is,
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+system calls such as
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+.BR write (2)
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+and
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+.BR pwrite (2).
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+.TP
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+.IR read_bytes ": bytes read"
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+Attempt to count the number of bytes which this process really did cause to
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+be fetched from the storage layer.
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+This is accurate for block-backed filesystems.
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+.TP
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+.IR write_bytes ": bytes written"
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+Attempt to count the number of bytes which this process caused to be sent to
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+the storage layer.
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+.TP
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+.IR cancelled_write_bytes :
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+The big inaccuracy here is truncate.
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+If a process writes 1MB to a file and then deletes the file,
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+it will in fact perform no writeout.
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+But it will have been accounted as having caused 1MB of write.
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+In other words: this field represents the number of bytes which this process
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+caused to not happen, by truncating pagecache.
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+A task can cause "negative" I/O too.
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+If this task truncates some dirty pagecache,
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+some I/O which another task has been accounted for
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+(in its
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+.IR write_bytes )
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+will not be happening.
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+.RE
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+.IP
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+.IR Note :
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+In the current implementation, things are a bit racy on 32-bit systems:
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+if process A reads process B's
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+.I /proc/[pid]/io
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+while process B is updating one of these 64-bit counters,
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+process A could see an intermediate result.
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+.RE
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.TP
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.IR /proc/[pid]/limits " (since kernel 2.6.24)"
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This file displays the soft limit, hard limit, and units of measurement
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