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.\" $FreeBSD: src/share/man/man5/tmpfs.5,v 1.7 2010/01/29 15:11:50 jh Exp $
.\"
.Dd February 2, 2010
.Dt TMPFS 5
.Os
.Sh NAME
.Nm tmpfs
.Nd "efficient memory file system"
.Sh SYNOPSIS
To compile this driver into the kernel,
place the following line in your
kernel configuration file:
.Bd -ragged -offset indent
.Cd "options TMPFS"
.Ed
.Pp
Alternatively, to load the driver as a
module at boot time, place the following line in
.Xr loader.conf 5 :
.Bd -literal -offset indent
tmpfs_load="YES"
.Ed
.Sh OPTIONS
The following options are available when
mounting
.Nm
file systems:
.Bl -tag -width indent
.It Cm gid
root group id.
.It Cm uid
root user id.
.It Cm mode
permissions in octal format.
.It Cm inodes
maximum number of inodes.
.It Cm size
maximum size for the file system.
.It Cm maxfilesize
maximum file size of the file system.
.El
.Sh DESCRIPTION
In the
.Dx
implementation,
.Nm
filesystems are backed by swap space.
Only memory pressure will cause data to be backed to swap.
Normal filesystem operations such as
.Fn fsync ,
buffer cache flushing, and vnode recycling have no effect.
.Pp
.Nm
stores meta-data in wired kernel memory.
Meta-data is not backed by swap so care must be taken if using
.Nm
to store large numbers of small files.
.Pp
It is recommended that a large amount of swap space be reserved on modern
.Dx
platforms to accommodate
.Nm
and other subsystems.
32-bit kernels can accommodate 32G of swap by default while 64-bit kernels
can accommodate 512G of swap by default.
These defaults can be increased though it should be noted that 32-bit
kernels are ultimately limited by the amount of KVM available in its
small 32-bit address space.
.Pp
.Nm
will allocate and deallocate swap backing store on the fly based on usage.
By default
.Nm
allows up to 100% of swap space to be used.
If this is not desirable then the size option should be used to limit
its size.
.Pp
Every option that accepts a numerical value as its argument can take a
trailing
.Sq b
to indicate bytes (the default), a trailing
.Sq k
to indicate kilobytes, a trailing
.Sq M
to indicate megabytes or a trailing
.Sq G
to indicate gigabytes.
Note that both lowercase and uppercase forms of these letters are allowed.
.Sh EXAMPLES
To mount a
.Nm
memory file system:
.Pp
.Dl "mount -t tmpfs tmpfs /tmp"
.Sh SEE ALSO
.Xr fstab 5 ,
.Xr mount_nfs 8 ,
.Xr mount_tmpfs 8 ,
.Xr swapcache 8
.Sh HISTORY
The
.Nm
driver first appeared in
.Dx 2.5 .
.Sh AUTHORS
.An -nosplit
The
.Nm
kernel implementation was written by
.An Julio M. Merino Vidal Aq Mt jmmv@NetBSD.org
as a Google SoC project.
.Pp
.An Rohit Jalan
and others ported it from
.Nx
to
.Fx .
.Pp
.An Naoya Sugioka
and others ported it from
.Nx
to
.Dx .
.Pp
This manual page was written by
.An Xin LI Aq Mt delphij@FreeBSD.org .
.Sh BUGS
To mount NFS exported
.Nm
.Dx
NFS client need to disable ReaddirPlus, see
.Xr mount_nfs 8 .