TMPFS

NAME

DESCRIPTION

The filesystem is automatically created when mounting a filesystem with the type tmpfs via a command such as the following:

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

A tmpfs filesystem has the following properties:

*

The filesystem can employ swap space when physical memory pressure demands it.

*

The filesystem consumes only as much physical memory and swap space as is required to store the current contents of the filesystem.

*

During a remount operation (mount -o remount), the filesystem size can be changed (without losing the existing contents of the filesystem).

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

Mount options

size=bytes

Specify an upper limit on the size of the filesystem. The size is given in bytes, and rounded up to entire pages.

The size may have a k, m, or g suffix for Ki, Mi, Gi (binary kilo (kibi), binary mega (mebi), and binary giga (gibi)).

The size may also have a % suffix to limit this instance to a percentage of physical RAM.

The default, when neither size nor nr_blocks is specified, is size=50%.

nr_blocks=blocks

The same as size, but in blocks of PAGE_CACHE_SIZE.

Blocks may be specified with k, m, or g suffixes like size, but not a % suffix.

nr_inodes=inodes

The maximum number of inodes for this instance. The default is half of the number of your physical RAM pages, or (on a machine with highmem) the number of lowmem RAM pages, whichever is smaller.

Inodes may be specified with k, m, or g suffixes like size, but not a % suffix.

mode=mode

Set initial permissions of the root directory.

gid=gid (since Linux 2.5.7)

Set the initial group ID of the root directory.

uid=uid (since Linux 2.5.7)

Set the initial user ID of the root directory.

huge=huge_option (since Linux 4.7.0)

Set the huge table memory allocation policy for all files in this instance (if CONFIG_TRANSPARENT_HUGE_PAGECACHE is enabled).

The huge_option value is one of the following:

never

Do not allocate huge pages. This is the default.

always

Attempt to allocate huge pages every time a new page is needed.

within_size

Only allocate huge page if it will be fully within i_size. Also respect fadvise(2)/madvise(2) hints

advise

Only allocate huge pages if requested with fadvise(2)/madvise(2).

deny

For use in emergencies, to force the huge option off from all mounts.

force

Force the huge option on for all mounts; useful for testing.

mpol=mpol_option (since Linux 2.6.15)

Set the NUMA memory allocation policy for all files in this instance (if CONFIG_NUMA is enabled).

The mpol_option value is one of the following:

default

Use the process allocation policy (see set_mempolicy(2)).

prefer:node

Preferably allocate memory from the given node.

bind:nodelist

Allocate memory only from nodes in nodelist.

interleave

Allocate from each node in turn.

interleave:nodelist

Allocate from each node of in turn.

local

Preferably allocate memory from the local node.

In the above, nodelist is a comma-separated list of decimal numbers and ranges that specify NUMA nodes. A range is a pair of hyphen-separated decimal numbers, the smallest and largest node numbers in the range. For example, mpol=bind:0-3,5,7,9-15.

VERSIONS

NOTES

The tmpfs filesystem supports extended attributes (see xattr(7)), but user extended attributes are not permitted.

An internal shared memory filesystem is used for System V shared memory (shmget(2)) and shared anonymous mappings (mmap(2) with the MAP_SHARED and MAP_ANONYMOUS flags). This filesystem is available regardless of whether the kernel was configured with the CONFIG_TMPFS option.

A tmpfs filesystem mounted at /dev/shm is used for the implementation of POSIX shared memory (shm_overview(7)) and POSIX semaphores (sem_overview(7)).

The amount of memory consumed by all tmpfs filesystems is shown in the Shmem field of /proc/meminfo and in the shared field displayed by free(1).

The tmpfs facility was formerly called shmfs.  

SEE ALSO

The kernel source files Documentation/filesystems/tmpfs.txt and Documentation/admin-guide/mm/transhuge.rst.  

COLOPHON

Index

NAME

DESCRIPTION

Mount options

VERSIONS

NOTES

SEE ALSO

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