NAME | DESCRIPTION | VERSIONS | NOTES | SEE ALSO | COLOPHON

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

NAME         top

       tmpfs - a virtual memory filesystem

DESCRIPTION         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 filesys‐
          tem.

       *  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 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, which‐
              ever is smaller.

              Inodes may be specified with k, m, or g suffixes like size,
              but not a % suffix.

       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_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
                     needed.

              within_size
                     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
                     fadvise(2)/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         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)), 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         top

       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/vm/transhuge.txt.

COLOPHON         top

       This page is part of release 4.16 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/.

Linux                            2018-02-09                         TMPFS(5)

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