NAME

       tmpfs - a virtual memory filesystem

DESCRIPTION

       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=huge_option (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 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) and madvise(2) hints

              advise Only allocate huge pages if requested with fadvise(2) or 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

       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)),  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

       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       and
       Documentation/admin-guide/mm/transhuge.rst.