iosnoop(1m) USER COMMANDS iosnoop(1m)
iosnoop - snoop I/O events as they occur. Uses DTrace.
iosnoop [-a|-A|-Deghinostv] [-d device] [-f filename] [-m mount_point] [-n name] [-p PID]
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.
-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
instance name to snoop (eg, dad0)
full pathname of file to snoop
mountpoint for filesystem to snoop
-p PID process ID
Default output, print I/O activity as it occurs,
Print human readable timestamps,
# iosnoop -v
Print major and minor numbers,
# iosnoop -N
Snoop events on the root filesystem only,
# iosnoop -m /
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-
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
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)
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
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.
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.
iosnoop will run forever until Ctrl-C is hit.
Brendan Gregg [Sydney, Australia]
version 1.50 Jul 25, 2005 iosnoop(1m)