tmpfs(5)

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 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

   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

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

   In order to for user-space  tools  and  applications  to  create  tmpfs
   filesystems,  the  kernel  must  be  configured  with  the CONFIG_TMPFS
   option.

   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

   df(1), du(1), mount(8)

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

COLOPHON

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   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/.

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