freebsd-dev/etc/mtree
Kirk McKusick c7996ddf80 Create a new GEOM utility, gunion(8).
The gunion(8) utility is used to track changes to a read-only disk on
a writable disk. Logically, a writable disk is placed over a read-only
disk. Write requests are intercepted and stored on the writable
disk. Read requests are first checked to see if they have been
written on the top (writable disk) and if found are returned. If
they have not been written on the top disk, then they are read from
the lower disk.

The gunion(8) utility can be especially useful if you have a large
disk with a corrupted filesystem that you are unsure of how to
repair. You can use gunion(8) to place another disk over the corrupted
disk and then attempt to repair the filesystem. If the repair fails,
you can revert all the changes in the upper disk and be back to the
unchanged state of the lower disk thus allowing you to try another
approach to repairing it. If the repair is successful you can commit
all the writes recorded on the top disk to the lower disk.

Another use of the gunion(8) utility is to try out upgrades to your
system. Place the upper disk over the disk holding your filesystem
that is to be upgraded and then run the upgrade on it. If it works,
commit it; if it fails, revert the upgrade.

Further details can be found in the gunion(8) manual page.

Reviewed by: Chuck Silvers, kib (earlier version)
tested by:   Peter Holm
Differential Revision: https://reviews.freebsd.org/D32697
2022-02-28 16:36:08 -08:00
..
BSD.debug.dist Merge llvm-project main llvmorg-13-init-16847-g88e66fa60ae5 2021-11-13 21:39:49 +01:00
BSD.include.dist Create a new GEOM utility, gunion(8). 2022-02-28 16:36:08 -08:00
BSD.lib32.dist Install 32-bit libcrypto engines in /usr/lib32/engines instead of 2020-06-01 18:58:09 +00:00
BSD.release.dist
BSD.root.dist Add support for jail.conf.d 2021-09-10 00:30:04 -05:00
BSD.sendmail.dist BSD.sendmail.dist: simplify mqueue group name setting 2020-03-22 16:55:20 +00:00
BSD.tests.dist Integrate contrib/file/tests with kyua/atf 2022-02-16 13:02:45 -06:00
BSD.usr.dist Append Keyboard Layout specified option for using VNC. 2022-01-20 23:49:27 +01:00
BSD.var.dist bhyve/snapshot: drop mkdir when creating the unix domain socket 2021-02-22 11:31:07 -09:00
Makefile libsoft: Remove support for installing libsoft 2022-01-06 22:34:10 -07:00
README

$FreeBSD$

Note: If you modify these files, please keep hier(7) updated!

These files are used to create empty file hierarchies for building the
system into.  Some notes about working with them are placed here to try
and keep them in good working order.

    a)  The files use 4 space indentation, and other than in the header
        comments, should not contain any tabs.  An indentation of 4 is
        preferable to the standard indentation of 8 because the indentation
        of levels in these files can become quite deep causing the line to
        overflow 80 characters.

        This also matches with the files generated when using the
        mtree -c option, which was implemented that way for the same reason.

    b)  Only directories should be listed here.

    c)  The listing should be kept in filename sorted order.

    d)  Sanity checking changes to these files can be done by following
        this procedure (the sed -e is ugly, but fixing mtree -c to
        not emit the trailing white space would be even uglier):

            mkdir /tmp/MTREE
            mtree -deU -f BSD.X.dist -p /tmp/MTREE
            mtree -cdin -k uname,gname,mode -p /tmp/MTREE | \
		sed -e 's/ *$//' >BSD.X.new
            diff -u BSD.X.dist BSD.X.new
            rm -r /tmp/MTREE

        Note that you will get some differences about /set lines,
        and uname= gname= on certain directory areas, mainly man page
        sections.  This is caused by mtree not having a look ahead
        mechanism for making better selections for these as it
        traverses the hierarchy.

        The BSD.X.new file should NOT be committed, as it will be missing
        the correct header, and important keywords like ``nochange''.
        Simply use the diff for a sanity check to make sure things are in
        the correct order and correctly indented.

    e)  Further sanity checking of the system builds with DESTDIR=/someplace
        are more complicated, but can often catch missing entries in these
        files.  I tend to run this more complete sanity check shortly after
        the target date for a new release is announced.

        If you want details on it bug me about it via email to
        rgrimes@FreeBSD.org.