TMPFS(5)                    Linux Programmer's Manual                   TMPFS(5)

       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 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:

              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

              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

              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:

              never  Do not allocate huge pages.  This is the default.

              always Attempt to allocate huge pages every time a new page is

                     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

              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

       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.

              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.

       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 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

       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

       The tmpfs facility was formerly called shmfs.

       df(1), du(1), memfd_create(2), mmap(2), set_mempolicy(2), shm_open(3),

       The kernel source files Documentation/filesystems/tmpfs.txt and

       This page is part of release 5.13 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

Linux                              2021-03-22                           TMPFS(5)