tmpfs(5) - Linux manual page (original) (raw)
tmpfs(5) File Formats Manual tmpfs(5)
NAME top
tmpfs - a virtual memory filesystemDESCRIPTION top
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 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 enabled.
**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**=_hugeoption_ (since Linux 4.7.0)
Set the huge table memory allocation policy for all files
in this instance (if **CONFIG_TRANSPARENT_HUGEPAGE** is
enabled).
The _hugeoption_ 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
_isize_. Also respect **fadvise**(2) and [madvise(2)](../man2/madvise.2.html)
hints
**advise** Only allocate huge pages if requested with
**fadvise**(2) or [madvise(2)](../man2/madvise.2.html).
**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**=_mpoloption_ (since Linux 2.6.15)
Set the NUMA memory allocation policy for all files in this
instance (if **CONFIG_NUMA** is enabled).
The _mpoloption_ value is one of the following:
**default**
Use the process allocation policy (see
[set_mempolicy(2)](../man2/set%5Fmempolicy.2.html)).
**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 top
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 top
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)](../man7/xattr.7.html)),
but _user_ extended attributes are not permitted.
An internal shared memory filesystem is used for System V shared
memory ([shmget(2)](../man2/shmget.2.html)) and shared anonymous mappings ([mmap(2)](../man2/mmap.2.html) 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)](../man7/shm%5Foverview.7.html)) and POSIX
semaphores ([sem_overview(7)](../man7/sem%5Foverview.7.html)).
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)](../man1/free.1.html).
The **tmpfs** facility was formerly called **shmfs**.SEE ALSO top
[df(1)](../man1/df.1.html), [du(1)](../man1/du.1.html), [memfd_create(2)](../man2/memfd%5Fcreate.2.html), [mmap(2)](../man2/mmap.2.html), [set_mempolicy(2)](../man2/set%5Fmempolicy.2.html),
[shm_open(3)](../man3/shm%5Fopen.3.html), [mount(8)](../man8/mount.8.html)
The kernel source files _Documentation/filesystems/tmpfs.txt_ and
_Documentation/admin-guide/mm/transhuge.rst_.COLOPHON top
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man-pages@man7.orgLinux man-pages 6.10 2024-05-02 tmpfs(5)
Pages that refer to this page:fallocate(2), lseek(2), madvise(2), memfd_create(2), mmap(2), remap_file_pages(2), seccomp_unotify(2), swapon(2), UFFDIO_API(2const), shm_open(3), filesystems(5), namespace.conf(5), proc_meminfo(5), proc_pid_status(5), proc_vmstat(5), sysfs(5), cgroups(7), keyrings(7), shm_overview(7), user_namespaces(7), mount(8), systemd-fstab-generator(8)