I found icmpping items become unsupported state when zabbix-server is interrupted by any signal, such as SIGUSR1 (runtime control) or others.

I tested on Zabbix-4.0.29 on CentOS 7, but it can occur on other versions and platforms.

Here is zabbix_server.log messages.

  7268:20210318:151118.309 item "test02:icmpping[,2,2000,,2000]" became not supported: fping failed: no output
  7276:20210318:151124.360 item "test01:icmpping[,2,2000,,2000]" became not supported: fping failed: 10.2.190.177 : [0], 84 bytes, 0.27 ms (0.27 avg, 0% loss)

It looks fping unexpectedly exited and zabbix-server could not get fping results.

I investigated the cause and figured out that fgets() returns NULL and set errno=EINTR if it is interrupted by a signal. But zabbix-server does not check errno and break fgets() loop.

So we maybe need to retry to call fgets() in the case. I made a patch to fix the problem. Would you mind checking it?

Steps to reproduce:

1. install zabbix-server
2. add hosts and configure icmpping items
3. keep executing runtime control many times (e.g., zabbix_server -R log_level_increase)
4. icmpping items become unsupported

Result:
zabbix-server can not get fping result and icmpping items become unsupported.
Expected:
icmpping does not become unsupported.

P.S., similar problems might occur elsewhere using fgets(), but I have not checked.