opensnoop - macOS

Overview

opensnoop is a powerful utility that continuously monitors file and directory openings within a specified scope. It provides detailed information about each access attempt, including the target file or directory, process ID (PID), process name, file access flags, and more. opensnoop is invaluable for debugging and troubleshooting file access issues, detecting unauthorized access, and gathering forensic evidence.

Syntax

opensnoop [-hvVaL] [-s set_size] [-t timeout] [ pid... | [ -n ] port ]

Options/Flags

  • -h, –help: Displays the help message.
  • -v, –verbose: Enables verbose output, providing additional information about each event.
  • -V, –version: Displays the version information.
  • -a, –all_events: Monitors all events, including file openings, reads, writes, and deletes.
  • -L, –listen_ports: Captures opensnoop events from a specified TCP/IP port.
  • -n, –numeric_pid: Displays PIDs in numeric form instead of resolving to process names.
  • -s set_size: Sets the maximum size (in bytes) of the buffer used to store events. Default: 4 MB.
  • -t timeout: Sets the maximum time (in seconds) to wait for events before terminating. Default: No timeout.

Examples

  • Monitor file openings for a specific process:
opensnoop -p 1234
  • Monitor file openings on port 8080 in numeric PID mode:
opensnoop -Ln 8080 -n
  • Monitor all events and capture data from port 443:
opensnoop -a -L 443

Common Issues

  • No events captured: Ensure the target process or port is active and performing file operations.
  • PID resolution issues: If PIDs are not resolved to process names, consider using -n to display numeric PIDs.
  • Buffer overflow: If the event buffer is overflowing, increase the buffer size using -s.

Integration

opensnoop can be integrated with other macOS commands for advanced tasks. For instance, opensnoop‘s output can be piped to grep to filter specific events:

opensnoop | grep "open"
  • lsof: Lists open files and processes.
  • fstat: Displays file status information.
  • strace: Traces system calls and signals.