You can enter the monitor start command to display real-time additions to system logs and trace files:
user@host> monitor start filename
When the device adds a record to the file specified by filename, the record is displayed on the screen. For example, if you have configured a system log file named system-log (by including the syslog statement at the [edit system] hierarchy level), you can enter the monitor start system-log command to display the records added to the system log.
To display a list of files that are being monitored, enter the monitor list command. To stop the display of records for a specified file, enter the monitor stop filename command.