Snoop I/O events as they occur. Uses DTrace.
Syntax iosnoop [-a|-A|-Deghinostv] [-d device] [-f filename] [-m mount_point] [-n name] [-p PID] Key -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
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.
iosnoop will run forever until Ctrl-C is hit.
Default output, print I/O activity as they are executed:
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 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
"Physical fitness is not only one of the most important keys to a healthy body, it is the basis of dynamic and creative intellectual activity" ~ John Fitzgerald Kennedy
dtrace - generic front-end to the DTrace facility
opensnoop - Snoop file opens as they occur
Top 10 DTrace scripts - Brandan Gregg (author of the dtrace book)