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man:tmpfs

TMPFS(5) Linux Programmer's Manual 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  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 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 filesys-

        tem).
     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   fad-
                   vise(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 test-
                   ing.
     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 num-
            bers 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

     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

     In order for user-space tools and applications to create tmpfs filesys-
     tems, 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

     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  Docu-
     mentation/vm/transhuge.txt.

COLOPHON

     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)

/data/webs/external/dokuwiki/data/pages/man/tmpfs.txt · Last modified: 2019/05/17 09:32 by 127.0.0.1

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