For ALSA MIDI sequencer, the patchbay program can create an input sequencer port, and subscribe it to System:announce (0:1) to receive ALSA notifications about these events: client start/exit, port start/exit, port subscribed/unsubscribed. You can try this with aseqdump, like the following sample session: $ aseqdump -p 0:1 Waiting for data. Press Ctrl+C to end. Source Event Ch Data 0:1 Port subscribed 0:1 -> 128:0 0:1 Client start client 129 0:1 Client start client 130 0:1 Port start 129:0 0:1 Port start 130:0 0:1 Client start client 131 0:1 Port start 131:0 0:1 Port subscribed 129:0 -> 131:0 ... 0:1 Port unsubscribed 129:0 -> 131:0 0:1 Port exit 129:0 0:1 Client exit client 129 0:1 Port exit 130:0 0:1 Client exit client 130 0:1 Port exit 131:0 0:1 Client exit client 131 ... Regards, Pedro