system.hostname returns ZBX_NOTSUPPORTED if parameter is specified on Linux. The parameter should be ignored according to documentation.

zabbix@linux-host:~$ zabbix_get -s localhost -k agent.version
2.2.2
zabbix@linux-host:~$ zabbix_get -s localhost -k system.hostname
linux-host
zabbix@linux-host:~$ zabbix_get -s localhost -k system.hostname[host]
ZBX_NOTSUPPORTED
zabbix@linux-host:~$ zabbix_get -s localhost -k system.hostname[netbios]
ZBX_NOTSUPPORTED