Installation script of linux classic server creates isc_monitor1 file with the root owner and group. (user that runs installation procedure).
As a result, server cannot access this file, hence monitoring capabilities does not work.

The bug is caused by code in linux/classic/postinstall.sh.in and classiclibrary.sh.in.

This code from postinstall.sh.in creates and assings correct (firebird) owner on sc_init1 isc_lock1 isc_event1 files:
 
    for i in isc_init1 isc_lock1 isc_event1
      do
        FileName=$i.`hostname`
        touch $FileName
      done

    # Create log
    touch firebird.log


    # Update ownership and SUID bits for programs.
    chown -R $RunUser:$RunUser $FBRootDir

isc_monitor1 file is created next by code in function fixFilePermissions from classiclibrary.sh.in

    for i in isc_init1 isc_lock1 isc_event1 isc_monitor1
    do
        FileName=$i.`hostname`
                touch $FileName
        chmod ug=rw,o= $FileName
    done

This code is not correct as it does not change owner of touched isc_* files.
IMHO there should be only one place in code that creates all of isc_* files and assigns correct permissions to them.