In this GRN, Marcel Moolenaar overhauled the logic for mounting
the root file system on bootup: |------------------------------------------------------------------------ |r214006 | marcel | 2010-10-17 22:01:53 -0700 (Sun, 17 Oct 2010) | 20 lines | | Re-implement the root mount logic using a recursive approach, whereby each |root file system (starting with devfs and a synthesized configuration) can |contain directives for mounting another file system as root. |------------------------------------------------------------------------ This commit adds a mount.conf(8) man page which documents the root mount logic. mount.conf(8) also provides some examples for the /.mount.conf file, which can be used to change the root mount behavior. Reviewed by: marcel bjk
This commit is contained in:
Craig Rodrigues
parent
171863ac75
commit
0d6422dd87
@ -3,7 +3,7 @@
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PROG= mount
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SRCS= mount.c mount_fs.c getmntopts.c vfslist.c
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MAN= mount.8
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MAN= mount.8 mount.conf.8
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# We do NOT install the getmntopts.3 man page.
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DPADD= ${LIBUTIL}
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252
sbin/mount/mount.conf.8
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252
sbin/mount/mount.conf.8
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.\" Copyright (c) 2013 Marcel Moolenaar
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.\" Copyright (c) 2013 Craig Rodrigues
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.\" All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE AUTHORS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHORS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" $FreeBSD$
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.\"
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.\"
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.Dd July 7, 2013
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.Dt MOUNT.CONF 8
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.Os
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.Sh NAME
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.Nm mount.conf
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.Nd root file system mount configuration file
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.Sh SYNOPSIS
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.Pa /.mount.conf
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.Sh DESCRIPTION
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During the bootup process, the
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.Fx
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kernel will try to mount the root file system
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using the logic in the
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.Fn vfs_mountroot
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function in
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.Pa src/sys/kern/vfs_mountroot.c .
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The root mount logic can be described as follows:
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.Bl -enum
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.It
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The kernel will synthesize in memory a config file
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with default directives for mounting
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the root file system.
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The logic for this is in
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.Fn vfs_mountroot_conf0 .
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.It
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The kernel will first mount
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.Xr devfs 8
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as the root file system.
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.It
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Next, the kernel will parse the in-memory config file created in step 1
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and try to mount the actual root file system.
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See
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.Sx FILE FORMAT
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for the format of the config file.
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.It
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When the actual root file system is mounted,
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.Xr devfs
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will be re-mounted on the
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.Pa /dev
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directory.
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.It
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If a
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.Pa /.mount.conf
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file does not exist in the root file system which was
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just mounted, the root mount logic stops here.
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.It
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If a
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.Pa /.mount.conf
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file exists in the root file system which was just mounted,
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this file will be parsed, and the kernel will use this new config
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file to try to re-mount the root file system.
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See
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.Sx FILE FORMAT
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for the format of the config file.
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.It
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If the new root file system has a
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.Pa /.mount
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directory, the old root file system will be re-mounted
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on
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.Pa /.mount .
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.It
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The root mount logic will go back to step 4.
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.El
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.Pp
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The root mount logic is recursive, and step 8 will
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be repeated as long as each new root file system
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which is mounted has a
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.Pa /.mount.conf
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file.
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.Sh FILE FORMAT
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The kernel parses each line in
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.Pa .mount.conf
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and then tries to perform the action specified on that line as soon as it is parsed.
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.Bl -tag -width "XXXXXXXXXX"
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.It Ic #
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A line beginning with a # is a comment and is ignored.
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.It Ic {FS}:{MOUNTPOINT} {OPTIONS}
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The kernel will try to mount this in an
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operation equivalent to:
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.Bd -literal -offset indent
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mount -t {FS} -o {OPTIONS} {MOUNTPOINT} /
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.Ed
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.Pp
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If this is successfully mounted,
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further lines in
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.Pa .mount.conf
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are ignored.
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If all lines in
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.Pa .mount.conf
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have been processed and no root file system has been successfully
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mounted, then the action specified by
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.Ic .onfail
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is performed.
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.It Ic .ask
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When the kernel processes this line, a
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.Li mountroot>
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command-line prompt is displayed.
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At this prompt, the operator can enter the
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the root mount.
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.It Ic .md Ar file
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Create a memory backed
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.Xr md 4
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virtual disk, using
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.Ar file
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as the backing store.
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.It Ic .onfail Ar [panic|reboot|retry|continue]
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If after parsing all the lines in
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.Pa .mount.conf
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the kernel is unable to mount a root file system,
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the
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.Ic .onfail
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directive tells the kernel what action to perform.
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.It Ic .timeout Ar N
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Before trying to mount a root file system,
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if the root mount device does not exist, wait at most
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.Ar N
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seconds for the device to appear before trying to mount it.
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If
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.Ic .timeout
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is not specified, the default timeout is 3 seconds.
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.El
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.Sh EXAMPLES
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The following example
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.Pa .mount.conf
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will direct the kernel to try mounting the root file system
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first as an ISO CD9660 file system on
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.Pa /dev/cd0 ,
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then if that does not work, as an ISO CD9660 file system on
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.Pa /dev/acd0 ,
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and then if that does not work, as a UFS file system on
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.Pa /dev/ada0s1a .
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If that does not work, a
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.Li mountroot>
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command-line prompt will be displayed where the operator
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can manually enter the root file system to mount.
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Finally if that does not work, the kernel will panic.
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.Bd -literal -offset indent
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.Li .onfail panic
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.LI .timeout 3
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cd9660:/dev/cd0 ro
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.Li .timeout 0
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cd9660:/dev/acd0 ro
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.Li .timeout 3
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ufs:/dev/ada0s1a
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.Li .ask
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.Ed
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.Pp
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The following example
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.Pa .mount.conf
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will direct the kernel to create a
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.Xr md 4
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memory disk attached to the file
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.Pa /data/OS-1.0.iso
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and then mount the ISO CD9660 file system
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on the md device which was just created.
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The last line is a comment which is ignored.
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.Bd -literal -offset indent
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.Li .timeout 3
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.Li .md /data/OS-1.0.iso
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.Li cd9600:/dev/md# ro
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.Li # Can also use cd9660:/dev/md0 ro
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.Ed
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.Pp
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The following example
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.Pa .mount.conf
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will direct the kernel to create a
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.Xr md 4
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memory disk attached to the file
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.Pa /data/base.ufs.uzip
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and then mount the UFS file system
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on the md uzip device which was just created
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by the
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.Xr geom_uzip 4
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driver.
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.Bd -literal -offset indent
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.Li .md /data/base.ufs.uzip
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.Li ufs:/dev/md#.uzip ro
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.Li # Can also use ufs:/dev/md0.uzip ro
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.Ed
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.Pp
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The following example
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.Pa .mount.conf
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will direct the kernel to do a unionfs
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mount on a directory
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.Pa /jail/freebsd-8-stable
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which has a
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.Xr chroot 2
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environment.
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.Bd -literal -offset indent
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.Li .timeout 3
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.Li unionfs:/jail/freebsd-8-stable
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.Ed
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.Sh NOTES
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For each root file system which is mounted, a
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.Pa /dev
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directory
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.Em must
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exist so that the root mount logic can properly re-mount
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.Xr devfs 8 .
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If this directory does not exist, the system
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may hang during the bootup process.
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.Sh SEE ALSO
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.Xr boot 8 ,
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.Xr boot.config 5 ,
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.Xr fstab 5 ,
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.Xr loader 8 ,
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.Xr mount 8 ,
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.Xr md 4 ,
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.Xr nmount 2
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.Sh HISTORY
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The
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.Nm
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file first appeared in
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.Fx 9.0 .
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.Sh AUTHORS
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.An -nosplit
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The root mount logic in the
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.Fx
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kernel which parses
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.Pa /.mount.conf
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was written by
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.An Marcel Moolenaar Aq marcel@FreeBSD.org .
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This man page was written by
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.An Craig Rodrigues Aq rodrigc@FreeBSD.org .
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