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. Behaviour 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.

print all data
dump all data, space delimited
print time delta, us (elapsed)
print device name
print device instance
print major and minor numbers
print disk delta time, us
print start time, us
print completion time, us
print completion time, string
instance name to snoop (eg, dad0)
full pathname of file to snoop
mountpoint for filesystem to snoop
process name
process ID

# iosnoop
# iosnoop -v
# iosnoop -N
# iosnoop -m /

User ID
Process ID
Parent Process ID
command name for the process
argument listing for the process
size of the operation, bytes
disk block for the operation (location. relative to this filesystem. more useful with the -N option to print major and minor numbers)
timestamp for the disk request, us
timestamp for the disk completion, us
elapsed time from request to completion, us (this is the elapsed time from the disk request (strategy) to the disk completion (iodone))
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 name
device instance number
direction, Read or Write
mount point
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 verbose descriptions explaining the output.

iosnoop will run forever until Ctrl-C is hit.

Brendan Gregg [Sydney, Australia]

iotop(1M), dtrace(1M)

July 25, 2005 version 1.50