freebsd/sbin/mdconfig/mdconfig.8

.\" Copyright (c) 1993 University of Utah.
.\" Copyright (c) 1980, 1989, 1991, 1993
.\"	The Regents of the University of California.  All rights reserved.
.\" Copyright (c) 2000
.\"	Poul-Henning Kamp  All rights reserved.
.\"
.\" This code is derived from software contributed to Berkeley by
.\" the Systems Programming Group of the University of Utah Computer
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.\"     @(#)vnconfig.8	8.1 (Berkeley) 6/5/93
.\" from: src/usr.sbin/vnconfig/vnconfig.8,v 1.19 2000/12/27 15:30:29
.\"
.\" $FreeBSD$
.\"
.Dd November 6, 2004
.Dt MDCONFIG 8
.Os
.Sh NAME
.Nm mdconfig
.Nd configure and enable memory disks
.Sh SYNOPSIS
.Nm
.Fl a
.Fl t Ar type
.Op Fl n
.Oo Fl o Oo Cm no Oc Ns Ar option Oc ...
.Op Fl f Ar file
.Op Fl s Ar size
.Op Fl S Ar sectorsize
.Op Fl u Ar unit
.Op Fl x Ar sectors/track
.Op Fl y Ar heads/cyl
.Nm
.Fl d
.Fl u Ar unit
.Nm
.Fl l
.Op Fl n
.Op Fl u Ar unit
.Sh DESCRIPTION
The
.Nm
utility configures and enables
.Xr md 4
devices.
.Pp
Options indicate an action to be performed:
.Bl -tag -width indent
.It Fl a
Attach a memory disk.
This will configure and attach a memory disk with the
parameters specified and attach it to the system.
.It Fl d
Detach a memory disk from the system and release all resources.
.It Fl t Ar type
Select the type of the memory disk.
.Bl -tag -width "preload"
.It Cm malloc
Storage for this type of memory disk is allocated with
.Xr malloc 9 .
This limits the size to the malloc bucket limit in the kernel.
If the
.Fl o Cm reserve
option is not set, creating and filling a large
malloc-backed memory disk is a very easy way to
panic a system.
.It Cm vnode
A file specified with
.Fl f Ar file
becomes the backingstore for this memory disk.
.It Cm swap
Swap space is used to back this memory disk.
.El
.It Fl f Ar file
Filename to use for the vnode type memory disk. Options
.Fl a
and
.Fl t Ar vnode
are implied if not specified.
.It Fl l
List configured devices.
If given with
.Fl u ,
display details about that particular device.
.It Fl n
When printing md device names, print only the unit number without the
md prefix.
.It Fl s Ar size
Size of the memory disk.
.Ar Size
is the number of 512 byte sectors unless suffixed with a
.Cm b , k , m , g ,
or
.Cm t
which
denotes byte, kilobyte, megabyte, gigabyte and terabyte respectively. Options
.Fl a
and
.Fl t Ar swap
are implied if not specified.
.It Fl S Ar sectorsize
Sectorsize to use for malloc backed device.
.It Fl x Ar sectors/track
See the description of the
.Fl y
option below.
.It Fl y Ar heads/cylinder
For
.Cm malloc
or
.Cm vnode
backed devices, the
.Fl x
and
.Fl y
options can be used to specify a synthetic geometry.
This is useful for constructing bootable images for later download to
other devices.
.It Fl o Oo Cm no Oc Ns Ar option
Set or reset options.
.Bl -tag -width indent
.It Oo Cm no Oc Ns Cm async
For
.Cm vnode
backed devices: avoid
.Dv IO_SYNC
for increased performance but
at the risk of deadlocking the entire kernel.
.It Oo Cm no Oc Ns Cm reserve
Allocate and reserve all needed storage from the start, rather than as needed.
.It Oo Cm no Oc Ns Cm cluster
Enable clustering on this disk.
.It Oo Cm no Oc Ns Cm compress
Enable/Disable compression features to reduce memory usage.
.It Oo Cm no Oc Ns Cm force
Disable/Enable extra sanity checks to prevent the user from doing something
that might adversely affect the system.
.It Oo Cm no Oc Ns Cm readonly
Enable/Disable readonly mode.
.El
.It Fl u Ar unit
Request a specific unit number for the
.Xr md 4
device instead of automatic allocation.
.El
.Sh EXAMPLES
To create a 4 megabyte
.Xr malloc 9
backed memory disk.
The name of the allocated unit will be output on stdout like
.Dq Li md3 :
.Pp
.Dl mdconfig -a -t malloc -s 4m
.Pp
To create a disk named
.Pa /dev/md4
with
.Pa /tmp/boot.flp
as backing:
.Pp
.Dl mdconfig -a -t vnode -f /tmp/boot.flp -u 4
.Pp
To detach and free all resources used by
.Pa /dev/md4 :
.Pp
.Dl mdconfig -d -u 4
.Pp
To create and mount a 128MByte swap backed file system on
.Pa /tmp :
.Bd -literal -offset indent
mdconfig -a -t swap -s 128M -u 10
newfs -U /dev/md10
mount /dev/md10 /tmp
chmod 1777 /tmp
.Ed
.Pp
To create a 5MB file-backed disk (
.Fl -a
and
.Fl -t Ar vnode
are implied):
.Bd -literal -offset indent
dd if=/dev/zero of=somebackingfile bs=1k count=5k
mdconfig -f somebackingfile -u 0
bsdlabel -w md0 auto
newfs md0c
mount /dev/md0c /mnt
.Ed
.Sh SEE ALSO
.Xr md 4 ,
.Xr bsdlabel 8 ,
.Xr fdisk 8 ,
.Xr mdmfs 8 ,
.Xr malloc 9
.Sh HISTORY
The
.Nm
utility first appeared in
.Fx 5.0
as a cleaner replacement for the
.Xr vn 4
and
.Xr vnconfig 8
combo.
.Sh AUTHORS
The
.Nm
utility was written by
.An Poul-Henning Kamp
.Aq phk@FreeBSD.org .