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
# Create 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
chmod ug=rw,o= $FileName
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.