The format of the message-source field in a message on a single-chassis system depends on whether the message was generated on the local Routing Engine or the other Routing Engine (on a system with two Routing Engines installed and operational). Messages from the other Routing Engine appear only if its configuration includes the other-routing-engine statement at the [edit system syslog host] hierarchy level.
hostname process[process-ID]
hostname reX process[process-ID]
hostname is the hostname of the local Routing Engine.
process[process-ID] is the name and PID of the process that generated the message. If the reX field also appears, the process is running on the other Routing Engine. If a process does not report its PID, the [process-ID] part does not appear.
reX indicates that the other Routing Engine generated the message (X is 0 or 1).