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 size option can be used to specify an upper limit on the size
          of the filesystem.  (The default size is half of the available RAM
          size.)  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).

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

       For a description of the mount options that may be employed when
       mounting a tmpfs filesystem, see mount(8).

       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 as 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), mount(8)

       The kernel source file Documentation/filesystems/tmpfs.txt.

COLOPHON         top

       This page is part of release 4.11 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                            2017-05-03                         TMPFS(5)

Pages that refer to this page: fallocate(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)cgroups(7)keyrings(7)user_namespaces(7)