iosnoop - macOS


iosnoop is a command-line utility used on macOS to monitor disk I/O activity in real time. Primarily developed for troubleshooting and analyzing system performance, it helps users and system administrators understand how different applications interact with the disk. This tool is especially valuable for performance analysis in development environments, debugging during application testing, and routine system monitoring.


The basic syntax of the iosnoop command is:

iosnoop [options]


iosnoop supports several options that modify its behavior:

  • -h: Display help message and exit.
  • -p PID: Only trace I/O for the provided process ID (PID).
  • -n NAME: Only trace I/O for processes with the given name.
  • -d DEVICE: Trace I/O on a specific device.
  • -f FILENAME: Trace I/O on the specified filename.
  • -v: Increase verbosity of the output.
  • -t: Include a timestamp in each output line.
  • -m MIN_MS: Trace only I/O operations that take longer than MIN_MS milliseconds.

Each option tailors the output of iosnoop to fit specific needs, helping filter and analyze disk I/O more efficiently.


  1. Basic Usage: Monitor all disk I/O activity.
  2. Filter by Process ID: Monitor disk I/O for a specific PID.
    iosnoop -p 1234
  3. Filter by Program Name: Monitor disk I/O for processes named “Finder”.
    iosnoop -n Finder
  4. Verbose Output with Timestamps: Get detailed output with timestamps for each I/O event.
    iosnoop -vt

Common Issues

  • Permission Errors: Users might encounter permission issues if iosnoop is not run as root. Using sudo to start iosnoop usually resolves these errors.
  • High Output Volume: In systems with heavy disk usage, the output can be overwhelming. Use filters like -p, -n, or -m to reduce output to manageable levels.


iosnoop can work collaboratively with other macOS tools:

  • grep: Filter output for specific data.
    iosnoop | grep "specific-data"
  • awk or sed: Analyze or format output.
    iosnoop | awk '{print $1, $2}'

For advanced monitoring, you can also script around iosnoop to trigger alerts or log data for later analysis.

  • iostat: Reports CPU statistics and I/O statistics for disks.
  • iotop: Display an updated list of disk I/O utilization by process.

For more details, consult the man pages of these commands or online resources specific to Unix-based system performance monitoring tools.