'\" te
.\" Copyright (c) 1990, Sun Microsystems, Inc.
.\" The contents of this file are subject to the terms of the Common Development and Distribution License (the "License").  You may not use this file except in compliance with the License.
.\" You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE or http://www.opensolaris.org/os/licensing.  See the License for the specific language governing permissions and limitations under the License.
.\" When distributing Covered Code, include this CDDL HEADER in each file and include the License file at usr/src/OPENSOLARIS.LICENSE.  If applicable, add the following below this CDDL HEADER, with the fields enclosed by brackets "[]" replaced with your own identifying information: Portions Copyright [yyyy] [name of copyright owner]
.TH TMPFS 7FS "Oct 9, 1990"
.SH NAME
tmpfs \- memory based file system
.SH SYNOPSIS
.LP
.nf
#include <sys/mount.h>

\fB\fR\fBmount\fR (\fB\fR\fIspecial\fR, \fB\fR\fIdirectory\fR, \fB\fR\fIMS_DATA\fR, \fB\fR\fI"tmpfs"\fR, \fB\fR\fINULL\fR, \fB\fR\fI0\fR);
.fi

.SH DESCRIPTION
.sp
.LP
\fBtmpfs\fR is a memory based file system which uses kernel resources relating
to the \fBVM\fR system and page cache as a file system. Once mounted, a
\fBtmpfs\fR file system provides standard file operations and semantics.
\fBtmpfs\fR is so named because files and directories are not preserved across
reboot or unmounts, all files residing on a  \fBtmpfs\fR file system that is
unmounted will be lost.
.sp
.LP
\fBtmpfs\fR file systems can be mounted with the command:
.sp
.in +2
.nf
\fBmount \fR\fB-F\fR\fB tmpfs swap \fR\fIdirectory\fR
.fi
.in -2

.sp
.LP
Alternatively, to mount a  \fBtmpfs\fR file system on \fB/tmp\fR at multi-user
startup time (maximizing possible performance improvements), add the following
line to \fB/etc/vfstab\fR:
.sp
.in +2
.nf
\fBswap \(mi/tmp tmpfs \(mi yes \(mi\fR
.fi
.in -2

.sp
.LP
\fBtmpfs\fR is designed as a performance enhancement which is achieved by
caching the writes to files residing on a  \fBtmpfs\fR file system. Performance
improvements are most noticeable when a large number of short lived files are
written and accessed on a \fBtmpfs\fR file system. Large compilations with
\fBtmpfs\fR mounted on \fB/tmp\fR are a good example of this.
.sp
.LP
Users of \fBtmpfs\fR should be aware of some constraints involved in mounting a
\fBtmpfs\fR file system. The resources used by \fBtmpfs\fR are the same as
those used when commands are executed (for example, swap space allocation).
This means that  large sized  \fBtmpfs\fR files can affect the amount of space
left over for programs to execute. Likewise, programs requiring large amounts
of memory use up the space available to \fBtmpfs\fR. Users running into this
constraint (for example, running out of space on \fBtmpfs\fR) can allocate more
swap space by using the \fBswap\fR(1M) command.
.sp
.LP
Another constraint is that the number of files available in a  \fBtmpfs\fR file
system is calculated based on the physical memory of the machine  and not the
size of the swap device/partition. If you have too many files, \fBtmpfs\fR will
print a warning message and you will be unable to create new files. You cannot
increase this limit by adding swap space.
.sp
.LP
Normal file system writes are scheduled to be written to a permanent storage
medium along with all control information associated with the file (for
example, modification time, file permissions). \fBtmpfs\fR control information
resides only in memory and never needs to be written to permanent storage. File
data remains in core until memory demands are sufficient to cause pages
associated with \fBtmpfs\fR to be reused at which time they are copied out to
swap.
.sp
.LP
An additional mount option can be specified to control the size of an
individual \fBtmpfs\fR file system.
.SH SEE ALSO
.sp
.LP
\fBdf\fR(1M), \fBmount\fR(1M), \fBmount_tmpfs\fR(1M), \fBswap\fR(1M),
\fBmmap\fR(2), \fBmount\fR(2), \fBumount\fR(2), \fBvfstab\fR(4)
.sp
.LP
\fISystem Administration Guide: Basic Administration\fR
.SH DIAGNOSTICS
.sp
.LP
If \fBtmpfs\fR runs out of space, one of the following messages will display in
the console.
.sp
.ne 2
.na
\fB\fB\fIdirectory\fR: File system full, swap space limit exceeded\fR\fR
.ad
.sp .6
.RS 4n
This message appears because a page could not be allocated while writing to a
file. This can occur if \fBtmpfs\fR is attempting to write more than it is
allowed, or if currently executing programs are using a lot of memory. To make
more space available, remove unnecessary files, exit from some programs, or
allocate more swap space using \fBswap\fR(1M).
.RE

.sp
.ne 2
.na
\fB\fB\fIdirectory\fR: File system full, memory allocation failed\fR\fR
.ad
.sp .6
.RS 4n
\fBtmpfs\fR ran out of physical memory while attempting to create a new file or
directory. Remove unnecessary files or directories or install more physical
memory.
.RE

.SH WARNINGS
.sp
.LP
Files and directories on a \fBtmpfs\fR file system are not preserved across
reboots or unmounts. Command scripts or programs which count on this will not
work as expected.
.SH NOTES
.sp
.LP
Compilers do not necessarily use \fB/tmp\fR to write intermediate files
therefore missing some significant performance benefits. This can be remedied
by setting the environment variable \fBTMPDIR\fR to \fB/tmp\fR. Compilers use
the value in this environment variable as the name of the directory to store
intermediate files.
.sp
.LP
\fBswap\fR to a \fBtmpfs\fR file is not supported.
.sp
.LP
\fBdf\fR(1M) output is of limited accuracy since a \fBtmpfs\fR file system size
is not static and the space available to \fBtmpfs\fR is dependent on the swap
space demands of the entire system.