# tmpfs

## 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 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 limit is removed if the size is **0**.
    
                  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.  The limit is removed if the
                  number is **0**.
    
                  Inodes may be specified with **k** , **m** , or **g** suffixes like **size** ,
                  but not a % suffix.
    
           **noswap**(since Linux 6.4)
                  Disables swap.  Remounts must respect the original
                  settings.  By default swap is enabled.
    
           **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_HUGEPAGE** 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) and madvise(2)
                         hints
    
                  **advise** Only allocate huge pages if requested with
                         **fadvise**(2) or 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



           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**
           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**.
    


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