tmpfs(5) — Linux manual page

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
          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 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.

              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/admin-guide/mm/transhuge.rst.

COLOPHON         top

       This page is part of release 5.11 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                          2021-03-22                       TMPFS(5)

Pages that refer to this page: fallocate(2)fanotify_mark(2)ioctl_userfaultfd(2)lseek(2)madvise(2)memfd_create(2)mmap(2)remap_file_pages(2)swapon(2)shm_open(3)filesystems(5)proc(5)sysfs(5)cgroups(7)keyrings(7)user_namespaces(7)mount(8)systemd-fstab-generator(8)