On any Linux OS only the root user is allowed to send ICMP echo requests. The distributions use different approaches to allow any user to use the
ping command. But these special rights don't apply to frontman.
In order to perform ICMP echo requests on CentOS6 you must allow any unprivileged user to do so. You do so by changing a kernel setting by executing the command
sysctl -w net.ipv4.ping_group_range="0 2147483647"
You can verify the command was successfully by executing
sysctl -a|grep net.ipv4.ping_group_range.
[[email protected] ~]# sysctl -a|grep net.ipv4.ping_group_rangenet.ipv4.ping_group_range = 0 2147483647
This command is executed during the installation of the RPM package in the background and normally you must not execute it manually. But in some cases, these settings are not written to disk so they don't survive a reboot. After a reboot frontman fails to execute ICMP echo requests and all your ping checks are marked as failed resulting in false alerts.
Right after the reboot check your kernel settings again. If you get the following results, the needed settings got lost.
[[email protected] ~]# sysctl -a|grep net.ipv4.ping_group_rangenet.ipv4.ping_group_range = 1 0
To make these settings reboot-safe, execute the following command. A reboot is not necessary.
echo 'net.ipv4.ping_group_range = 0 2147483647' > /etc/sysctl.d/net-ipv4.confsysctl -w net.ipv4.ping_group_range="0 2147483647"