fb14e73cb4
superblock has a check-hash error, an error message noting the superblock check-hash failure is printed and the mount fails. The administrator then runs fsck to repair the filesystem and when successful, the filesystem can once again be mounted. This approach fails if the filesystem in question is a root filesystem from which you are trying to boot. Here, the loader fails when trying to access the filesystem to get the kernel to boot. So it is necessary to allow the loader to ignore the superblock check-hash error and make a best effort to read the kernel. The filesystem may be suffiently corrupted that the read attempt fails, but there is no harm in trying since the loader makes no attempt to write to the filesystem. Once the kernel is loaded and starts to run, it attempts to mount its root filesystem. Once again, failure means that it breaks to its prompt to ask where to get its root filesystem. Unless you have an alternate root filesystem, you are stuck. Since the root filesystem is initially mounted read-only, it is safe to make an attempt to mount the root filesystem with the failed superblock check-hash. Thus, when asked to mount a root filesystem with a failed superblock check-hash, the kernel prints a warning message that the root filesystem superblock check-hash needs repair, but notes that it is ignoring the error and proceeding. It does mark the filesystem as needing an fsck which prevents it from being enabled for writing until fsck has been run on it. The net effect is that the reboot fails to single user, but at least at that point the administrator has the tools at hand to fix the problem. Reported by: Rick Macklem (rmacklem@) Discussed with: Warner Losh (imp@) Sponsored by: Netflix
FreeBSD Source:
This is the top level of the FreeBSD source directory. This file
was last revised on:
FreeBSD
FreeBSD is an operating system used to power modern servers, desktops, and embedded platforms. A large community has continually developed it for more than thirty years. Its advanced networking, security, and storage features have made FreeBSD the platform of choice for many of the busiest web sites and most pervasive embedded networking and storage devices.
For copyright information, please see the file COPYRIGHT in this directory. Additional copyright information also exists for some sources in this tree - please see the specific source directories for more information.
The Makefile in this directory supports a number of targets for building components (or all) of the FreeBSD source tree. See build(7), config(8), https://www.freebsd.org/doc/en_US.ISO8859-1/books/handbook/makeworld.html, and https://www.freebsd.org/doc/en_US.ISO8859-1/books/handbook/kernelconfig.html for more information, including setting make(1) variables.
Source Roadmap:
bin System/user commands.
cddl Various commands and libraries under the Common Development
and Distribution License.
contrib Packages contributed by 3rd parties.
crypto Cryptography stuff (see crypto/README).
etc Template files for /etc.
gnu Various commands and libraries under the GNU Public License.
Please see gnu/COPYING* for more information.
include System include files.
kerberos5 Kerberos5 (Heimdal) package.
lib System libraries.
libexec System daemons.
release Release building Makefile & associated tools.
rescue Build system for statically linked /rescue utilities.
sbin System commands.
secure Cryptographic libraries and commands.
share Shared resources.
stand Boot loader sources.
sys Kernel sources.
sys/<arch>/conf Kernel configuration files. GENERIC is the configuration
used in release builds. NOTES contains documentation of
all possible entries.
tests Regression tests which can be run by Kyua. See tests/README
for additional information.
tools Utilities for regression testing and miscellaneous tasks.
usr.bin User commands.
usr.sbin System administration commands.
For information on synchronizing your source tree with one or more of the FreeBSD Project's development branches, please see:
https://www.freebsd.org/doc/en_US.ISO8859-1/books/handbook/current-stable.html