GNU bug report logs - #23496
grub2 does not support the legacy command "write"

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Elmar Stellnberger <estellnb <at> elstel.org>
To: submit <at> debbugs.gnu.org
Subject: grub2 does not support the legacy command "write"
Date: Mon, 9 May 2016 19:26:06 +0200

   Package: grub
   Version: 1:2.02.beta2-6

   I have tried to dd the boot image of the Ultimate Boot CD into a 
hard disk partition in order to boot it from there. Then I have 
converted the menu.lst as used by Grub1 on that CD image by 
grub-menulst2cfg. As it turned out most entries are no more bootable 
with grub2 because of the 'write' command being no more supported. As 
Jordan_U has told me on #grub this command would no more be supported 
due to security reasons.
  However my objection against abandoning support for the write command 
is that it can happily and safely be used together with ram disks as the 
Ultimate Boot CD does.
  Anyone here who would mind to implement the write command for Grub2? 
I would really believe that Grub2 should be backward compatible!
  Using Grub1 in addition to Grub2 has not proven to be a good 
alternative as it can not access iso9660 file systems when booted over a 
virtual floppy image. Up to now there is also no CD emulation; what 
works with Grub1 though is to enter the following manually when booting 
with another old physical grub1-bootcd:

  root (hd0,17)
  configfile (hd0,17)/boot/grub/menu.lst

Message #8 received at 23496 <at> debbugs.gnu.org (full text, mbox):

From: Elmar Stellnberger <estellnb <at> elstel.org>
To: 23496 <at> debbugs.gnu.org
Subject: Re: bug#23496: Acknowledgement (grub2 does not support the legacy
 command "write")
Date: Mon, 9 May 2016 23:08:34 +0200

  My idea about the write command is that it could serve as a 
replacement for kernel parameters whenever an OS needs to be 
chainloaded. That way also non-directly supported OSes like Windows or 
DOS or any new not yet supported ones could be customized.

  The command found for fdubcd.img.gz is:
write --offset=15 /bin/setargs.bat ubcdcmd=keydisk\r\n

It simply replaces the given file for the given string at the given 
offset. The file itself contains sufficient spaces at the given position 
in order to hold for the parameter passed via write. As already said 
there are no additional security/safety considerations necessary as long 
as the file resides inside a RAM disk.

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