mount.conf
— root
file system mount configuration file
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:
- 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
().
- The kernel will first mount
devfs(5)
as the root file system.
- 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.
- When the actual root file system is mounted,
devfs(5)
will be re-mounted on the /dev directory.
- If a /.mount.conf file does not exist in the root
file system which was just mounted, the root mount logic stops here.
- 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.
- If the new root file system has a /.mount
directory, the old root file system will be re-mounted on
/.mount.
- 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.
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.
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
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.
The mount.conf
file first appeared in
FreeBSD 9.0.
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>.