tmpfs - a virtual memory filesystem
The 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.
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
- 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
If a tmpfs filesystem is unmounted, its contents are
The tmpfs filesystem supports the following mount options:
- 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,
- 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.
- 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.
- 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:
- Do not allocate huge pages. This is the default.
- Attempt to allocate huge pages every time a new page is needed.
- Only allocate huge page if it will be fully within i_size. Also
respect fadvise(2)/madvise(2) hints
- Only allocate huge pages if requested with
- For use in emergencies, to force the huge option off from all mounts.
- 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:
- Use the process allocation policy (see set_mempolicy(2)).
- Preferably allocate memory from the given node.
- Allocate memory only from nodes in nodelist.
- Allocate from each node in turn.
- Allocate from each node of in turn.
- Preferably allocate memory from the local node.
The tmpfs facility was added in Linux 2.4, as a successor to the older
ramfs facility, which did not provide limit checking or allow for the
use of swap space.
In order for user-space tools and applications to create tmpfs
filesystems, the kernel must be configured with the CONFIG_TMPFS
- 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
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
A tmpfs filesystem mounted at /dev/shm is used for
the implementation of POSIX shared memory (shm_overview(7)) and POSIX
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.
df(1), du(1), memfd_create(2), mmap(2),
set_mempolicy(2), shm_open(3), mount(8)
The kernel source files Documentation/filesystems/tmpfs.txt
This page is part of release 5.05 of the Linux 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/.