# man > tmpfs(5) [_tmpfs_(5)](https://www.chedong.com/phpMan.php/man/tmpfs/5/markdown) File Formats Manual [_tmpfs_(5)](https://www.chedong.com/phpMan.php/man/tmpfs/5/markdown) ## NAME tmpfs - a virtual memory filesystem ## DESCRIPTION The **tmpfs **facility allows the creation of filesystems whose contents reside in virtual mem‐ ory. 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 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 The **tmpfs **filesystem supports the following 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 limit is removed if the size is **0**. 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. The limit is removed if the number is **0**. Inodes may be specified with **k**, **m**, or **g **suffixes like **size**, but not a % suffix. **noswap**(since Linux 6.4) Disables swap. Remounts must respect the original settings. By default swap is en‐ abled. **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 **CON‐** **FIG_TRANSPARENT_HUGEPAGE **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 **fad‐** [**vise**(2)](https://www.chedong.com/phpMan.php/man/vise/2/markdown) and [**madvise**(2)](https://www.chedong.com/phpMan.php/man/madvise/2/markdown) hints **advise **Only allocate huge pages if requested with [**fadvise**(2)](https://www.chedong.com/phpMan.php/man/fadvise/2/markdown) or [**madvise**(2)](https://www.chedong.com/phpMan.php/man/madvise/2/markdown). **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)](https://www.chedong.com/phpMan.php/man/setmempolicy/2/markdown)). **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 small‐ est and largest node numbers in the range. For example, _mpol=bind:0-3,5,7,9-15_. ## VERSIONS 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. ## NOTES In order for user-space tools and applications to create **tmpfs **filesystems, the kernel must be configured with the **CONFIG_TMPFS **option. The **tmpfs **filesystem supports extended attributes (see [**xattr**(7)](https://www.chedong.com/phpMan.php/man/xattr/7/markdown)), but _user_ extended attrib‐ utes are not permitted. An internal shared memory filesystem is used for System V shared memory ([**shmget**(2)](https://www.chedong.com/phpMan.php/man/shmget/2/markdown)) and shared anonymous mappings ([**mmap**(2)](https://www.chedong.com/phpMan.php/man/mmap/2/markdown) 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)](https://www.chedong.com/phpMan.php/man/shmoverview/7/markdown)) and POSIX semaphores ([**sem_overview**(7)](https://www.chedong.com/phpMan.php/man/semoverview/7/markdown)). 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)](https://www.chedong.com/phpMan.php/man/free/1/markdown). The **tmpfs **facility was formerly called **shmfs**. ## SEE ALSO [**df**(1)](https://www.chedong.com/phpMan.php/man/df/1/markdown), [**du**(1)](https://www.chedong.com/phpMan.php/man/du/1/markdown), [**memfd_create**(2)](https://www.chedong.com/phpMan.php/man/memfdcreate/2/markdown), [**mmap**(2)](https://www.chedong.com/phpMan.php/man/mmap/2/markdown), [**set_mempolicy**(2)](https://www.chedong.com/phpMan.php/man/setmempolicy/2/markdown), [**shm_open**(3)](https://www.chedong.com/phpMan.php/man/shmopen/3/markdown), [**mount**(8)](https://www.chedong.com/phpMan.php/man/mount/8/markdown) The kernel source files _Documentation/filesystems/tmpfs.txt_ and _Documentation/ad‐_ _min-guide/mm/transhuge.rst_. Linux man-pages 6.7 2023-10-31 [_tmpfs_(5)](https://www.chedong.com/phpMan.php/man/tmpfs/5/markdown)