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. Be-
       haviour such as random or sequential I/O can be observed by reading the block numbers.

       Since this uses DTrace, only users with root privileges 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  num-
	      bers)

       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 ver-
       bose 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)