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.TH TMPFS 5 2017-05-03 "Linux" "Linux Programmer's Manual"

.SH NAME

tmpfs \- a virtual memory filesystem

.SH DESCRIPTION

The

.B tmpfs

facility allows the creation of filesystems whose contents reside

in virtual memory.

Since the files on such filesystems typically reside in RAM,

file access is extremely fast.

.PP

The filesystem is automatically created when mounting

a filesystem with the type

.BR tmpfs

via a command such as the following:

.PP

.in +4n

.EX

$ sudo mount \-t tmpfs -o size=10M tmpfs /mnt/mytmpfs

.EE

.in

.PP

A

.B tmpfs

filesystem has the following properties:

.IP * 3

The filesystem can employ swap space when physical memory pressure

demands it.

.IP *

The

.I size

option can be used to specify an upper limit on the size of the filesystem.

(The default size is half of the available RAM size.)

The filesystem consumes only as much physical memory and swap space

as is required to store the current contents of the filesystem.

.IP *

During a remount operation

.RI ( "mount\ \-o\ remount" ),

the filesystem size can be changed

(without losing the existing contents of the filesystem).

.PP

If a

.B tmpfs

filesystem is unmounted, its contents are discarded (lost).

.SH VERSIONS

The

.B tmpfs

facility was added in Linux 2.4, as a successor to the older

.B ramfs

facility, which did not provide limit checking or

allow for the use of swap space.

.SH NOTES

For a description of the mount options that may be employed when mounting a

.B tmpfs

filesystem, see

.BR mount (8).

.PP

In order for user-space tools and applications to create

.B tmpfs

filesystems, the kernel must be configured with the

.B CONFIG_TMPFS

option.

.PP

The

.BR tmpfs

filesystem supports extended attributes (see

.BR xattr (7)),

but

.I user

extended attributes are not permitted.

.PP

An internal shared memory filesystem is used for

System V shared memory

.RB ( shmget (2))

and shared anonymous mappings

.RB ( mmap (2)

with the

.B MAP_SHARED

and

.BR MAP_ANONYMOUS

flags).

This filesystem is available regardless of whether

the kernel was configured with the

.B CONFIG_TMPFS

option.

.PP

A

.B tmpfs

filesystem mounted at

.IR /dev/shm

as used for the implementation of POSIX shared memory

.RB ( shm_overview (7))

and POSIX semaphores

.RB ( sem_overview (7)).

.PP

The amount of memory consumed by all

.B tmpfs

filesystems is shown in the

.I Shmem

field of

.IR /proc/meminfo

and in the

.I shared

field displayed by

.BR free (1).

.PP

The

.B tmpfs

facility was formerly called

.BR shmfs .

.SH SEE ALSO

.BR df (1),

.BR du (1),

.BR memfd_create (2),

.BR mmap (2),

.BR shm_open (3),

.BR mount (8)

.PP

The kernel source file

.IR Documentation/filesystems/tmpfs.txt .

.SH COLOPHON

This page is part of release 4.15 of the Linux

.I man-pages

project.

A description of the project,

information about reporting bugs,

and the latest version of this page,

can be found at

\%https://www.kernel.org/doc/man\-pages/.