ntop doesn't start - open of /var/lib/ntop/prefsCache.db failed: Can't be writer

Question

I've installed ntop on centos 5.9 using yum. But it doesn't start. I'm getting this error:

 Wed Mar 20 10:22:44 2013  **ERROR** ....open of /var/lib/ntop/prefsCache.db failed: Can't be writer
Wed Mar 20 10:22:44 2013  Possible solution: please use '-P <directory>'
Wed Mar 20 10:22:44 2013  **FATAL_ERROR** GDBM open failed, ntop shutting down...
Wed Mar 20 10:22:44 2013  CLEANUP[t47669729537792]: ntop caught signal 2 [state=2]
Wed Mar 20 10:22:44 2013  ntop is now quitting...
Wed Mar 20 10:25:01 2013  NOTE: Interface merge enabled by default
Wed Mar 20 10:25:01 2013  Initializing gdbm databases
Wed Mar 20 10:25:01 2013  **ERROR** ....open of /var/lib/ntop/prefsCache.db failed: Can't be writer
Wed Mar 20 10:25:01 2013  Possible solution: please use '-P <directory>'
Wed Mar 20 10:25:01 2013  **FATAL_ERROR** GDBM open failed, ntop shutting down...
Wed Mar 20 10:25:01 2013  CLEANUP[t47959862075136]: ntop caught signal 2 [state=2]
Wed Mar 20 10:25:01 2013  ntop is now quitting...

I set permissions 777 to /var/lib/ntop and all files in it. Still doesn't work.

Solution 1

Fixed it by killing ntop service, changing owner to ntop and starting it again

Solution 2

Try entering

ps -ax | grep ntop

into terminal to view ntop processes running, then type

sudo kill-9 (process #'s)

replacing (process #'s) with the process ids shown.

Make sure that when your done using ntop you ctrl+C to quit, not ctrl+z. Using control z leaves a "stray" ntop program running.