Updated grub.cfg with explanation

files/grub.cfg

@@ -1,8 +1,35 @@
+# This file was deployed by Puppet and is under Smart Proxy control. Click on
+# "Build PXE Default" button to overwrite it. Puppet is prevented managing this
+# file by default, this can be enforced via --foreman-proxy-tftp-replace-grub2-cfg
+# foreman-installer option or Puppet parameter.
+
 insmod regexp
 
-set net_pxe_mac=$net_default_mac
+# On Debian/Ubuntu grub2 does not have patch for loading MAC-based configs. Also due to bug
+# in RHEL 7.4 files are loaded with an extra ":" character at the end. This workarounds both
+# cases, make sure "regexp.mod" file is present on the TFTP. For more info see:
+# https://bugzilla.redhat.com/show_bug.cgi?id=1370642#c70
 regexp --set=1:m1 --set=2:m2 --set=3:m3 --set=4:m4 --set=5:m5 --set=6:m6 '^([0-9a-f]{1,2})\:([0-9a-f]{1,2})\:([0-9a-f]{1,2})\:([0-9a-f]{1,2})\:([0-9a-f]{1,2})\:([0-9a-f]{1,2})' "$net_default_mac"
-mac_dashed=${m1}-${m2}-${m3}-${m4}-${m5}-${m6}
+mac=${m1}-${m2}-${m3}-${m4}-${m5}-${m6}
+configfile=/grub2/grub.cfg-01-$mac
+source "$configfile"
+
+# If MAC-specific config is not found, attempt to boot from local drive.
+
+default=local_chain_hd0
+timeout=20
+
+menuentry 'Chainload into BIOS bootloader on first disk' --id local_chain_hd0 {
+  set root=(hd0,0)
+  chainloader +1
+}
+
+menuentry 'Chainload into BIOS bootloader on second disk' --id local_chain_hd1 {
+  set root=(hd1,0)
+  chainloader +1
+}
 
-mac_configfile=$prefix/grub.cfg-01-$mac_dashed
-source "$mac_configfile"
+menuentry 'Third disk - for EFI or Discovery click on Build PXE Default'' --id local_chain_hd2 {
+  set root=(hd2,0)
+  chainloader +1
+}