check program times out

Dear list,

I’m trying to monitor an USB port.

The script „checkUSB.sh“ returns „error“ or „exists“ (successfully tested in Terminal as root).

Monit runs as root but with

check program checkUSB with path "/usr/local/sbin/checkUSB.sh"
    if content != "exists" then alert

never returns. The process runs forever and is then killed by timeout.

Apr  1 08:19:01 asterisk monit[5301]: 'checkUSB' program timed out after 5.017 m. Killing program with pid 5321
Apr  1 08:19:01 asterisk monit[5301]: 'checkUSB' content match on program output:#012#012
Apr  1 08:24:02 asterisk monit[5301]: 'checkUSB' program timed out after 5.017 m. Killing program with pid 5527
Apr  1 08:24:02 asterisk monit[5301]: 'checkUSB' content match on program output:#012#012
Apr  1 08:29:03 asterisk monit[5301]: 'checkUSB' program timed out after 5.017 m. Killing program with pid 5560
Apr  1 08:29:03 asterisk monit[5301]: 'checkUSB' content match on program output:#012#012

What could be wrong here?

Thanks in advance!

Tino