.\" Copyright (c) 1996
.\"	Mike Pritchard <mpp@FreeBSD.org>.  All rights reserved.
.\"
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.\" Jan-Simon Pendry.
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.Dd June 30, 2022
.Dt DEVFS 4
.Os
.Sh NAME
.Nm devfs
.Nd device file system
.Sh SYNOPSIS
.Bd -literal
devfs	/dev	devfs rw 0 0
.Ed
.Sh DESCRIPTION
The device file system, or
.Nm ,
provides access to kernel's device
namespace in the global file system namespace.
The conventional mount point is
.Pa /dev .
.Pp
The file system includes several directories, links, symbolic links
and devices, some of which can also be written.
In a chroot'ed
environment,
.Xr devfs 8
can be used to create a new
.Pa /dev
mount point.
.Pp
The
.Xr mknod 8
tool can be used to recover deleted device entries under
.Nm .
.Pp
The
.Xr fdescfs 4
filesystem is an alternate means for populating
.Pa /dev/fd .
The character devices that both
.Nm
and
.Xr fdescfs 4
present in
.Pa /dev/fd
correspond to the open file descriptors of the process
accessing the directory.
.Nm
only creates files for the standard file descriptors
.Pa 0 ,
.Pa 1
and
.Pa 2 .
.Xr fdescfs 4
creates files for all open descriptors.
.Pp
The options are as follows:
.Bl -tag -width indent
.It Fl o Ar options
Use the specified mount
.Ar options ,
as described in
.Xr mount 8 .
The following devfs file system-specific options are available:
.Bl -tag -width indent
.It Cm ruleset Ns No = Ns Ar ruleset
Set ruleset number
.Ar ruleset
as the current ruleset for the mount-point and apply all its rules.
If the ruleset number
.Ar ruleset
does not exist, an empty ruleset with the number
.Ar ruleset
is created.
See
.Xr devfs 8
for more information on working with devfs rulesets.
.El
.El
.Sh FILES
.Bl -tag -width /dev/XXXX -compact
.It Pa /dev
The normal
.Nm
mount point.
.El
.Sh EXAMPLES
To mount a
.Nm
volume located on
.Pa /mychroot/dev :
.Pp
.Dl "mount -t devfs devfs /mychroot/dev"
.Sh SEE ALSO
.Xr fdescfs 4 ,
.Xr devfs 8 ,
.Xr mount 8 ,
.Xr make_dev 9
.Sh HISTORY
The
.Nm
file system first appeared in
.Fx 2.0 .
It became the preferred method for accessing devices in
.Fx 5.0
and the only method in
.Fx 6.0 .
The
.Nm
manual page first appeared in
.Fx 2.2 .
.Sh AUTHORS
The
.Nm
manual page was written by
.An Mike Pritchard Aq Mt mpp@FreeBSD.org .