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iosnoop(1m)                                     USER COMMANDS                                    iosnoop(1m)



NAME
       iosnoop - snoop I/O events as they occur. Uses DTrace.

SYNOPSIS
       iosnoop [-a|-A|-Deghinostv] [-d device] [-f filename] [-m mount_point] [-n name] [-p PID]

DESCRIPTION
       iosnoop  prints  I/O events as they happen, with useful details such as UID, PID, block number, size,
       filename, etc.

       This is useful to determine the process responsible for using the disks, as well as details  on  what
       activity  the  process  is  requesting. Behaviour such as random or sequential I/O can be observed by
       reading the block numbers.

       Since this uses DTrace, only the root user or users with the dtrace_kernel  privilege  can  run  this
       command.

OPTIONS
       -a     print all data

       -A     dump all data, space delimited

       -D     print time delta, us (elapsed)

       -e     print device name

       -i     print device instance

       -n     print major and minor numbers

       -o     print disk delta time, us

       -s     print start time, us

       -t     print completion time, us

       -v     print completion time, string

       -d device
              instance name to snoop (eg, dad0)

       -f filename
              full pathname of file to snoop

       -m mount_point
              mountpoint for filesystem to snoop

       -n name
              process name

       -p PID process ID


EXAMPLES
       Default output, print I/O activity as it occurs,
              # iosnoop


       Print human readable timestamps,
              # iosnoop -v


       Print major and minor numbers,
              # iosnoop -n


       Snoop events on the root filesystem only,
              # iosnoop -m /


FIELDS
       UID    User ID

       PID    Process ID

       PPID   Parent Process ID

       COMM   command name for the process

       ARGS   argument listing for the process

       SIZE   size of the operation, bytes

       BLOCK  disk  block for the operation (location. relative to this filesystem.  more useful with the -n
              option to print major and minor numbers)

       STIME  timestamp for the disk request, us

       TIME   timestamp for the disk completion, us

       DELTA  elapsed time from request to completion, us (this is the elapsed time from  the  disk  request
              (strategy) to the disk completion (iodone))

       DTIME  time  for  disk  to complete request, us (this is the time for the disk to complete that event
              since it's last event (time between iodones), or, the time to the strategy  if  the  disk  had
              been idle)

       STRTIME
              timestamp for the disk completion, string

       DEVICE device name

       INS    device instance number

       D      direction, Read or Write

       MOUNT  mount point

       FILE   filename (basename) for I/O operation


NOTES
       When  filtering on PID or process name, be aware that poor disk event times may be due to events that
       have been filtered away, for example another process that may be seeking the disk heads elsewhere.


DOCUMENTATION
       See the DTraceToolkit for further documentation under the Docs directory. The DTraceToolkit docs  may
       include full worked examples with verbose descriptions explaining the output.

EXIT
       iosnoop will run forever until Ctrl-C is hit.

AUTHOR
       Brendan Gregg [Sydney, Australia]

SEE ALSO
       iotop(1M), dtrace(1M)




version 1.50                                    Jul 25, 2005                                     iosnoop(1m)