Date: Sun, 12 May 2013 23:54:45 -0400 (EDT) From: Garrett Wollman <wollman@hergotha.csail.mit.edu> To: jdc@koitsu.org Cc: freebsd-stable@freebsd.org Subject: Re: Reinstalling boot blocks on a ZFS-only system Message-ID: <201305130354.r4D3sjUu017172@hergotha.csail.mit.edu> In-Reply-To: <20130513032838.GA76253@icarus.home.lan> References: <A6940C2F-17B4-4ECF-85B6-BA8CB335486E@distal.com> <201305130314.r4D3EKaJ016781@hergotha.csail.mit.edu>
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In article <20130513032838.GA76253@icarus.home.lan>, jdc@koitsu.org write: >https://wiki.freebsd.org/RootOnZFS/GPTZFSBoot > >5. Install the Protected MBR (pmbr) and gptzfsboot loader Bug #1: "Protective", not "Protected". > Fixit# gpart bootcode -b /mnt2/boot/pmbr -p /mnt2/boot/gptzfsboot -i 1 ad0 > > This may fail with an "operation not permitted" error message, since the > kernel likes to protect critical parts of the disk. If this happens for > you, run: > > Fixit# sysctl kern.geom.debugflags=0x10 I suppose the bit that's missing here is: ...and then file a bug report, with severity "serious" and priority "high", because this indicates that something is seriously broken in the kernel's implementation of GPT partitioning. The only way this step can fail (absent bugs) is if something (other than gpart) has either the whole-disk device or the partition 1 device open in exclusive mode, which is a "can't happen" condition at this stage in an installation. (Well, it can happen if the disk you are in the process of destroying has a still-mounted filesystem on it, which is what the code is supposed to prevent!) This little bit of cargo-culting used to be necessary for *MBR* and *bsdlabel* partitioning, before the days of "gpart bootcode", to update the boot0 and embedded partition-boot (boot1) blocks while the filesystem was mounted, because the bsdlabel boot blocks are stored in the first 64k of the root filesystem. When using GPT, the boot blocks are stored in the boot partition, which doesn't have a mountable filesystem on it, so should never be open for write except when gpart bootcode is doing the deed. -GAWollman
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