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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	 typi-
       cally 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

       *  During  a  remount operation (mount -o remount), the filesystem size
	  can be changed (without losing the existing contents of the filesys-

       If a tmpfs filesystem is unmounted, its contents are discarded (lost).

       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.

       For a description of the mount options that may be employed when mount-
       ing 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

       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

       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), mount(8)

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

       This  page  is  part of release 4.10 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				  2016-11-07			      TMPFS(5)