mount.conf.8

.\" Copyright (c) 2013 Marcel Moolenaar
.\" Copyright (c) 2013 Craig Rodrigues
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.Dd October 17, 2013
.Dt MOUNT.CONF 8
.Os
.Sh NAME
.Nm mount.conf
.Nd root file system mount configuration file
.Sh SYNOPSIS
.Pa /.mount.conf
.Sh DESCRIPTION
During the bootup process, the
.Fx
kernel will try to mount the root file system
using the logic in the
.Fn vfs_mountroot
function in
.Pa src/sys/kern/vfs_mountroot.c .
The root mount logic can be described as follows:
.Bl -enum
.It
The kernel will synthesize in memory a config file
with default directives for mounting
the root file system.
The logic for this is in
.Fn vfs_mountroot_conf0 .
.It
The kernel will first mount
.Xr devfs 8
as the root file system.
.It
Next, the kernel will parse the in-memory config file created in step 1
and try to mount the actual root file system.
See
.Sx FILE FORMAT
for the format of the config file.
.It
When the actual root file system is mounted,
.Xr devfs 5
will be re-mounted on the
.Pa /dev
directory.
.It
If a
.Pa /.mount.conf
file does not exist in the root file system which was
just mounted, the root mount logic stops here.
.It
If a
.Pa /.mount.conf
file exists in the root file system which was just mounted,
this file will be parsed, and the kernel will use this new config
file to try to re-mount the root file system.
See
.Sx FILE FORMAT
for the format of the config file.
.It
If the new root file system has a
.Pa /.mount
directory, the old root file system will be re-mounted
on
.Pa /.mount .
.It
The root mount logic will go back to step 4.
.El
.Pp
The root mount logic is recursive, and step 8 will
be repeated as long as each new root file system
which is mounted has a
.Pa /.mount.conf
file.
.Sh FILE FORMAT
The kernel parses each line in
.Pa .mount.conf
and then tries to perform the action specified on that line as soon as it is parsed.
.Bl -tag -width "XXXXXXXXXX"
.It Ic #
A line beginning with a # is a comment and is ignored.
.It Ic {FS}:{MOUNTPOINT} {OPTIONS}
The kernel will try to mount this in an
operation equivalent to:
.Bd -literal -offset indent
mount -t {FS} -o {OPTIONS} {MOUNTPOINT} /
.Ed
.Pp
If this is successfully mounted,
further lines in
.Pa .mount.conf
are ignored.
If all lines in
.Pa .mount.conf
have been processed and no root file system has been successfully
mounted, then the action specified by
.Ic .onfail
is performed.
.It Ic .ask
When the kernel processes this line, a
.Li mountroot>
command-line prompt is displayed.
At this prompt, the operator can enter the
the root mount.
.It Ic .md Ar file
Create a memory backed
.Xr md 4
virtual disk, using
.Ar file
as the backing store.
.It Ic .onfail Ar [panic|reboot|retry|continue]
If after parsing all the lines in
.Pa .mount.conf
the kernel is unable to mount a root file system,
the
.Ic .onfail
directive tells the kernel what action to perform.
.It Ic .timeout Ar N
Before trying to mount a root file system,
if the root mount device does not exist, wait at most
.Ar N
seconds for the device to appear before trying to mount it.
If
.Ic .timeout
is not specified, the default timeout is 3 seconds.
.El
.Sh EXAMPLES
The following example
.Pa .mount.conf
will direct the kernel to try mounting the root file system
first as an ISO CD9660 file system on
.Pa /dev/cd0 ,
then if that does not work, as an ISO CD9660 file system on
.Pa /dev/cd1 ,
and then if that does not work, as a UFS file system on
.Pa /dev/ada0s1a .
If that does not work, a
.Li mountroot>
command-line prompt will be displayed where the operator
can manually enter the root file system to mount.
Finally if that does not work, the kernel will panic.
.Bd -literal -offset indent
.Li .onfail panic
.Li .timeout 3
cd9660:/dev/cd0 ro
.Li .timeout 0
cd9660:/dev/cd1 ro
.Li .timeout 3
ufs:/dev/ada0s1a
.Li .ask
.Ed
.Pp
The following example
.Pa .mount.conf
will direct the kernel to create a
.Xr md 4
memory disk attached to the file
.Pa /data/OS-1.0.iso
and then mount the ISO CD9660 file system
on the md device which was just created.
The last line is a comment which is ignored.
.Bd -literal -offset indent
.Li .timeout 3
.Li .md /data/OS-1.0.iso
.Li cd9600:/dev/md# ro
.Li # Can also use cd9660:/dev/md0 ro
.Ed
.Pp
The following example
.Pa .mount.conf
will direct the kernel to create a
.Xr md 4
memory disk attached to the file
.Pa /data/base.ufs.uzip
and then mount the UFS file system
on the md uzip device which was just created
by the
.Xr geom_uzip 4
driver.
.Bd -literal -offset indent
.Li .md /data/base.ufs.uzip
.Li ufs:/dev/md#.uzip ro
.Li # Can also use ufs:/dev/md0.uzip ro
.Ed
.Pp
The following example
.Pa .mount.conf
will direct the kernel to do a unionfs
mount on a directory
.Pa /jail/freebsd-8-stable
which has a
.Xr chroot 2
environment.
.Bd -literal -offset indent
.Li .timeout 3
.Li unionfs:/jail/freebsd-8-stable
.Ed
.Sh NOTES
For each root file system which is mounted, a
.Pa /dev
directory
.Em must
exist so that the root mount logic can properly re-mount
.Xr devfs 8 .
If this directory does not exist, the system
may hang during the bootup process.
.Sh SEE ALSO
.Xr nmount 2 ,
.Xr md 4 ,
.Xr boot.config 5 ,
.Xr fstab 5 ,
.Xr boot 8 ,
.Xr loader 8 ,
.Xr mount 8
.Sh HISTORY
The
.Nm
file first appeared in
.Fx 9.0 .
.Sh AUTHORS
.An -nosplit
The root mount logic in the
.Fx
kernel which parses
.Pa /.mount.conf
was written by
.An Marcel Moolenaar Aq Mt marcel@FreeBSD.org .
This man page was written by
.An Craig Rodrigues Aq Mt rodrigc@FreeBSD.org .