MOUNT.CONF(5) FreeBSD File Formats Manual MOUNT.CONF(5)
NAME
mount.conf - root file system mount configuration file
SYNOPSIS
/.mount.conf
DESCRIPTION
During the bootup process, the FreeBSD kernel will try to mount the root
file system using the logic in the vfs_mountroot() function in
src/sys/kern/vfs_mountroot.c. The root mount logic can be described as
follows:
1. The kernel will synthesize in memory a config file with default
directives for mounting the root file system. The logic for this is
in vfs_mountroot_conf0().
2. The kernel will first mount devfs(5) as the root file system.
3. Next, the kernel will parse the in-memory config file created in
step 1 and try to mount the actual root file system. See FILE
FORMAT for the format of the config file.
4. When the actual root file system is mounted, devfs(5) will be re-
mounted on the /dev directory.
5. If a /.mount.conf file does not exist in the root file system which
was just mounted, the root mount logic stops here.
6. If a /.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 FILE
FORMAT for the format of the config file.
7. If the new root file system has a /.mount directory, the old root
file system will be re-mounted on /.mount.
8. The root mount logic will go back to step 4.
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 /.mount.conf file.
FILE FORMAT
The kernel parses each line in .mount.conf and then tries to perform the
action specified on that line as soon as it is parsed.
# A line beginning with a # is a comment and is ignored.
{FS}:{MOUNTPOINT} {OPTIONS}
The kernel will try to mount this in an operation equivalent
to:
mount -t {FS} -o {OPTIONS} {MOUNTPOINT} /
If this is successfully mounted, further lines in .mount.conf
are ignored. If all lines in .mount.conf have been processed
and no root file system has been successfully mounted, then
the action specified by .onfail is performed.
.ask When the kernel processes this line, a mountroot> command-
line prompt is displayed. At this prompt, the operator can
enter the root mount.
.md file Create a memory backed md(4) virtual disk, using file as the
backing store.
.onfail [panic|reboot|retry|continue]
If after parsing all the lines in .mount.conf the kernel is
unable to mount a root file system, the .onfail directive
tells the kernel what action to perform.
.timeout N Before trying to mount a root file system, if the root mount
device does not exist, wait at most N seconds for the device
to appear before trying to mount it. If .timeout is not
specified, the default timeout is 3 seconds.
EXAMPLES
The following example .mount.conf will direct the kernel to try mounting
the root file system first as an ISO CD9660 file system on /dev/cd0, then
if that does not work, as an ISO CD9660 file system on /dev/cd1, and then
if that does not work, as a UFS file system on /dev/ada0s1a. If that
does not work, a 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.
.onfail panic
.timeout 3
cd9660:/dev/cd0 ro
.timeout 0
cd9660:/dev/cd1 ro
.timeout 3
ufs:/dev/ada0s1a
.ask
The following example .mount.conf will direct the kernel to create a
md(4) memory disk attached to the file /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.
.timeout 3
.md /data/OS-1.0.iso
cd9600:/dev/md# ro
# Can also use cd9660:/dev/md0 ro
The following example .mount.conf will direct the kernel to create a
md(4) memory disk attached to the file /data/base.ufs.uzip and then mount
the UFS file system on the md uzip device which was just created by the
geom_uzip(4) driver.
.md /data/base.ufs.uzip
ufs:/dev/md#.uzip ro
# Can also use ufs:/dev/md0.uzip ro
The following example .mount.conf will direct the kernel to do a unionfs
mount on a directory /jail/freebsd-8-stable which has a chroot(2)
environment.
.timeout 3
unionfs:/jail/freebsd-8-stable
NOTES
For each root file system which is mounted, a /dev directory must exist
so that the root mount logic can properly re-mount devfs(5). If this
directory does not exist, the system may hang during the bootup process.
SEE ALSO
nmount(2), md(4), boot.config(5), fstab(5), boot(8), loader(8), mount(8)
HISTORY
The mount.conf file first appeared in FreeBSD 9.0.
AUTHORS
The root mount logic in the FreeBSD kernel which parses /.mount.conf was
written by Marcel Moolenaar <marcel@FreeBSD.org>. This man page was
written by Craig Rodrigues <rodrigc@FreeBSD.org>.
FreeBSD 13.1-RELEASE-p6 October 17, 2013 FreeBSD 13.1-RELEASE-p6
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