Please note that if netxmsd is started without root permissions, ICMP and SNMP traps will not work (RAW sockets required for ICMP and SNMP traps are received on port 162).
If you running modern Linux you can set capabilities to overcome that:
sudo /sbin/setcap cap_net_bind_service,cap_net_raw=ep /opt/netxms/bin/netxmsd
To verify:
1) check with getcap:$ /sbin/getcap /opt/netxms/bin/netxmsd
/opt/netxms/bin/netxmsd = cap_net_bind_service,cap_net_raw+ep
2) This error should not appear anymore on log file: "[ERROR] Unable to bind socket to port 162 in function SNMPTrapReceiver: Permission denied"
P.S. setcap/getcap are from package libcap2-bin