Rosegarden supports the JACK transport mechanism for synchronising its transport with other JACK applications on the same computer. To activate it, go to -> and check the box.
When the JACK transport is in use, all of the applications that are subscribed to it share a common transport control, and you can start, stop, and move the transport from any one of them.
Many Linux audio applications that use the JACK audio server also support JACK transport: consult their documentation for details of whether and how.
Rosegarden supports MIDI Time Code (MTC) synchronisation in master and slave modes. This is particularly useful for synchronising the Rosegarden transport with a hardware MTC-capable device, or with software running on other computers connected via MIDI.
To make Rosegarden the MTC Master, so that it will control any MTC slave device or application connected to it, go to -> and in the MIDI page's MIDI Sync tab, select "MTC Master" from the MIDI Time Code menu. To make Rosegarden an MTC Slave so that Rosegarden's transport will automatically be synchronised with incoming MTC events, select "MTC Slave".