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.Dd June 2, 2018
.Dt INITRD 7
.Os
.Sh NAME
.Nm initrd
.Nd initial ramdisk image as early userland
.Sh DESCRIPTION
The
.Nm
is a small initial ramdisk image that packs a minimal
.Xr init 8 ,
basic
.Xr rc 8
scripts, and many other statically linked tools, such as various
.Xr mount 8
utilities,
.Xr lvm 8 ,
.Xr cryptsetup 8 ,
.Xr tcplay 8 ,
as well as some networking tools.
The
.Nm
is a nice early userland and is required to help mount the root
partition residing on an encrypted device or LVM.
.Pp
The statically linked tools are known as the
.Dq rescue tools
and shipped at
.Pa /rescue .
The inclusion of such rescue tools makes
.Nm
can provide with a powerful rescue environment to fix severe problems,
e.g., the root partition cannot be mounted.
Users can also choose to boot into the rescue mode from the bootloader
menu.
.Pp
The
.Nm
is a
.Xr md 4
image formatted with the
.Xr UFS 5
filesystem.
It is created by the
.Dq initrd
target of the
.Xr build 7
framework, and is compressed and installed at
.Pa /boot/kernel/initrd.img.gz .
The following configurations should be added to
.Pa /boot/loader.conf
to make use of the
.Nm
image:
.Bd -literal -offset indent
initrd.img_load="YES"
initrd.img_type="md_image"
vfs.root.mountfrom="ufs:md0s0"
.Ed
.Pp
Then, the
.Dq vfs.root.realroot
kernel environment variable can be configured to specify how to
mount the real root partition.
Its general syntax is:
.Bd -literal -offset indent
vfs.root.realroot="<type>:[arg1[:arg2[:...]]]"
.Ed
.Pp
Currently, the supported types of real root partition are:
.Pa local ,
.Pa crypt ,
and
.Pa tcplay .
The
.Pa local
type allows to mount any local filesystem that does not require any
special setup apart from the initial discovery and calling the
.Xr mount 8
program.
The general format is as follows:
.Bd -literal -offset indent
vfs.root.realroot="local:<FS-TYPE>:<DEVICE-PATH>[:<OPTIONS>]"
.Ed
.Pp
The
.Pa crypt
and
.Pa tcplay
types allow to mount volumes supported by
.Xr cryptsetup 8
and
.Xr tcplay 8 ,
respectively.
The device will be set up after asking the user for the key,
and this volume will then be mounted as the root.
The general formats are as follows:
.Bd -literal -offset indent
vfs.root.realroot="crypt:<FS-TYPE>:<DEVICE-PATH>:<MAPPING-NAME>[:<OPTIONS>]"

vfs.root.realroot="tcplay:<FS-TYPE>:<DEVICE-PATH>:<MAPPING-NAME>[:<OPTIONS>]"
.Ed
.Sh FILES
.Bl -tag -width "/boot/kernel/initrd.img.gz"
.It Pa /boot/kernel/initrd.img.gz
Location of the compressed
.Nm
image.
.El
.Sh EXAMPLES
.Bd -literal -offset indent
vfs.root.realroot="local:ufs:/dev/vg00/lv0[:OPTIONS]"

vfs.root.realroot="crypt:ufs:/dev/ad0s0a:secvolume[:OPTIONS]"

vfs.root.realroot="crypt:hammer2:/dev/serno/XXXXXX.s1d:root[:OPTIONS]"
.Ed
.Sh SEE ALSO
.Xr md 4 ,
.Xr loader.conf 5 ,
.Xr build 7 ,
.Xr cryptsetup 8 ,
.Xr lvm 8 ,
.Xr tcplay 8
.Sh HISTORY
The
.Nm
manual page first appeared in
.Dx 5.3 .
.Sh AUTHORS
The
.Nm
manual page was written by
.An Aaron LI Aq Mt aly@aaronly.me .
.Sh BUGS
The
.Nm
image occupies about 10-15 MB wired memory and cannot be freed after
chrooting to the real root partition.