$ ping 8.8.8.8 ping: socket: Operation not permitted
# setcap cap_net_admin,cap_net_raw+p /bin/ping
# getcap /bin/ping /bin/ping = cap_net_admin,cap_net_raw+p
$ ping 8.8.8.8 PING 8.8.8.8 (8.8.8.8) 56(84) bytes of data.
If You occured the problem in /var/log/zabbix-agent/zabbix_agentd.log
Message from <Zabbix Server IP> is missing header. Message ignored.
Downgrade Zabbix Agent from 4.x to your server version.
# apt-get remove zabbix-agent
Download appropriate version from http://repo.zabbix.com/zabbix/3.0/debian/pool/main/z/zabbix/
# wget http://repo.zabbix.com/zabbix/3.0/debian/pool/main/z/zabbix/zabbix-agent_3.0.28-1%2Bbuster_amd64.deb
install it
# dpkg -i zabbix-agent_3.0.28-1+buster_amd64.deb
lock if for future upgrades
# apt-mark hold zabbix-agent
unmask
# systemctl unmask zabbix-agent
enable and start
# systemctl enable zabbix-agent
# systemctl start zabbix-agent
Stop avahi
# systemctl disable avahi-daemon
Enable rc.local capability/compatibility
# echo $'#!/bin/sh -e\nexit 0'