Fixed hostname validation and write behavior

src/include/network/services/dns.rb

@@ -64,7 +64,7 @@ def initialize_network_services_dns(include_target)
       @widget_descr_dns = {
         "HOSTNAME"        => {
           "widget"            => :textentry,
-          "label"             => Label.HostName,
+          "label"             => "Static H&ostname",
           "opt"               => [],
           "help"              => Ops.get_string(@help, "hostname_global", ""),
           "valid_chars"       => Hostname.ValidChars,
@@ -433,15 +433,10 @@ def HandleResolverData(key, _event)
     # @param _event [Hash] the event being handled
     # @return whether valid
     def ValidateHostname(key, _event)
-      dhn = dhcp? && use_dhcp_hostname?
-      # If the names are set by dhcp, the user may enter backup values
-      # here - N#28427. That is, host and domain name are optional then.
-      # For static config, they are mandatory.
-      value = Convert.to_string(UI.QueryWidget(Id(key), :Value))
-
-      return Hostname.Check(value) if !dhn || value != ""
+      value = UI.QueryWidget(Id(key), :Value).to_s
 
-      true
+      # empty hostname is allowed - /etc/hostname gets cleared in such case
+      value.empty? || Hostname.Check(value)
     end
 
     # Validator for the search list

src/lib/y2network/sysconfig/hostname_writer.rb

@@ -73,8 +73,10 @@ def update_sysconfig_dhcp(hostname, old_hostname)
       #
       # @param hostname [Y2Network::Hostname] Hostname configuration
       def update_hostname(hostname)
-        Yast::Execute.on_target!("/usr/bin/hostname", hostname.hostname.split(".")[0])
-        Yast::SCR.Write(Yast::Path.new(".target.string"), HOSTNAME_PATH, "#{hostname.hostname}\n")
+        # 1) when user asked for ereasing hostname from /etc/hostname, we keep runtime as it is
+        # 2) we will write whatever user wants even FQDN - no changes under the hood
+        Yast::Execute.on_target!("/usr/bin/hostname", hostname.static) if !hostname.static.empty?
+        Yast::SCR.Write(Yast::Path.new(".target.string"), HOSTNAME_PATH, hostname.static.empty? ? hostname.static : "#{hostname.static}\n")
       end
     end
   end