aseqdump

aseqdump [-h | -v] [-p client[:port]] [-s size] [-t time]

-h, --help
    Display usage summary and exit.

-v, --version
    Print version information and exit.

-p, --port client[:port]
    Subscribe to queue of given client and port (default: system:timer). Use aseqlist to list ports.

-s, --bufsize size
    Set maximum sysex buffer size in bytes (default: 512).

-t, --timeout time
    Set read timeout in seconds (default: 1).

aseqdump is a command-line utility from the ALSA (Advanced Linux Sound Architecture) utils package. It monitors and prints MIDI events from specified ALSA sequencer ports in human-readable text format, making it ideal for debugging MIDI applications, sequencer connections, and audio workflows.

By default, it subscribes to the system:timer port and outputs events like note-on/note-off, control changes, program changes, sysex messages, and timestamps to stdout. Each event shows details such as type, channel, key, velocity, and parameter values. This verbosity helps diagnose timing issues, connection problems, or unexpected MIDI data in Linux sound setups.

aseqdump runs continuously until interrupted (Ctrl+C), using non-blocking reads with a configurable timeout. It's lightweight, requires no special MIDI hardware, and works with software synthesizers or virtual ports created by tools like aconnect.

Common use cases include testing MIDI keyboards, inspecting JACK/ALSA bridges, or logging sequencer activity for analysis.

Requires read access to ALSA sequencer (/dev/snd/seq). High event rates may flood output or consume CPU. Does not support input ports natively; use with aconnect for routing. Interrupt with Ctrl+C.

aseqdump -p 14:0
Monitor default ALSA MIDI input port.

aseqdump -p hw:0,0 > midi.log
Dump events to file for later review.

type=NoteOn abs=12345.678 ch=0 note=60 vel=100
type=Control abs=12346.012 ch=0 ctrl=7 val=100

Part of alsa-utils since ALSA 0.9.x (circa 2002). Developed by ALSA team for sequencer debugging; evolved with kernel sequencer API changes in Linux 2.6+.

aconnect(1), aseqlist(1), amidi(1), aseqnet(1)