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-.\" Copyright (c) 2016 by Michael Kerrisk <mtk.manpages@gmail.com>
-.\"
-.\" SPDX-License-Identifier: Linux-man-pages-copyleft
-.\"
-.TH tmpfs 5 2023-10-31 "Linux man-pages 6.7"
-.SH NAME
-tmpfs \- a virtual memory filesystem
-.SH DESCRIPTION
-The
-.B 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.
-.P
-The filesystem is automatically created when mounting
-a filesystem with the type
-.B tmpfs
-via a command such as the following:
-.P
-.in +4n
-.EX
-$ sudo mount \-t tmpfs \-o size=10M tmpfs /mnt/mytmpfs
-.EE
-.in
-.P
-A
-.B tmpfs
-filesystem has the following properties:
-.IP \[bu] 3
-The filesystem can employ swap space when physical memory pressure
-demands it.
-.IP \[bu]
-The filesystem consumes only as much physical memory and swap space
-as is required to store the current contents of the filesystem.
-.IP \[bu]
-During a remount operation
-.RI ( "mount\ \-o\ remount" ),
-the filesystem size can be changed
-(without losing the existing contents of the filesystem).
-.P
-If a
-.B tmpfs
-filesystem is unmounted, its contents are discarded (lost).
-.\" See mm/shmem.c:shmem_parse_options for options it supports.
-.SS Mount options
-The
-.B tmpfs
-filesystem supports the following mount options:
-.TP
-.BR size "=\fIbytes\fP"
-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
-.BR 0 .
-.IP
-The size may have a
-.BR k ,
-.BR m ,
-or
-.B g
-suffix for Ki, Mi, Gi (binary kilo (kibi), binary mega (mebi), and binary giga
-(gibi)).
-.IP
-The size may also have a % suffix to limit this instance to a percentage of
-physical RAM.
-.IP
-The default, when neither
-.B size
-nor
-.B nr_blocks
-is specified, is
-.IR size=50% .
-.TP
-.BR nr_blocks "=\fIblocks\fP"
-The same as
-.BR size ,
-but in blocks of
-.BR PAGE_CACHE_SIZE .
-.IP
-Blocks may be specified with
-.BR k ,
-.BR m ,
-or
-.B g
-suffixes like
-.BR size ,
-but not a % suffix.
-.TP
-.BR nr_inodes "=\fIinodes\fP"
-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
-.BR 0 .
-.IP
-Inodes may be specified with
-.BR k ,
-.BR m ,
-or
-.B g
-suffixes like
-.BR size ,
-but not a % suffix.
-.TP
-.BR noswap "(since Linux 6.4)"
-.\" commit 2c6efe9cf2d7841b75fe38ed1adbd41a90f51ba0
-Disables swap.
-Remounts must respect the original settings.
-By default swap is enabled.
-.TP
-.BR mode "=\fImode\fP"
-Set initial permissions of the root directory.
-.TP
-.BR gid "=\fIgid\fP (since Linux 2.5.7)"
-.\" Technically this is also in some version of Linux 2.4.
-.\" commit 099445b489625b80b1d6687c9b6072dbeaca4096
-Set the initial group ID of the root directory.
-.TP
-.BR uid "=\fIuid\fP (since Linux 2.5.7)"
-.\" Technically this is also in some version of Linux 2.4.
-.\" commit 099445b489625b80b1d6687c9b6072dbeaca4096
-Set the initial user ID of the root directory.
-.TP
-.BR huge "=\fIhuge_option\fR (since Linux 4.7.0)"
-.\" commit 5a6e75f8110c97e2a5488894d4e922187e6cb343
-Set the huge table memory allocation policy for all files in this instance (if
-.B CONFIG_TRANSPARENT_HUGEPAGE
-is enabled).
-.IP
-The
-.I huge_option
-value is one of the following:
-.RS
-.TP
-.B never
-Do not allocate huge pages.
-This is the default.
-.TP
-.B always
-Attempt to allocate huge pages every time a new page is needed.
-.TP
-.B within_size
-Only allocate huge page if it will be fully within
-.IR i_size .
-Also respect
-.BR fadvise (2)
-and
-.BR madvise (2)
-hints
-.TP
-.B advise
-Only allocate huge pages if requested with
-.BR fadvise (2)
-or
-.BR madvise (2).
-.TP
-.B deny
-For use in emergencies, to force the huge option off from all mounts.
-.TP
-.B force
-Force the huge option on for all mounts; useful for testing.
-.RE
-.TP
-.BR mpol "=\fImpol_option\fR (since Linux 2.6.15)"
-.\" commit 7339ff8302fd70aabf5f1ae26e0c4905fa74a495
-Set the NUMA memory allocation policy for all files in this instance (if
-.B CONFIG_NUMA
-is enabled).
-.IP
-The
-.I mpol_option
-value is one of the following:
-.RS
-.TP
-.B default
-Use the process allocation policy (see
-.BR set_mempolicy (2)).
-.TP
-.BR prefer ":\fInode\fP"
-Preferably allocate memory from the given
-.IR node .
-.TP
-.BR bind ":\fInodelist\fP"
-Allocate memory only from nodes in
-.IR nodelist .
-.TP
-.B interleave
-Allocate from each node in turn.
-.TP
-.BR interleave ":\fInodelist\fP"
-Allocate from each node of
-.I in
-turn.
-.TP
-.B local
-Preferably allocate memory from the local node.
-.RE
-.IP
-In the above,
-.I 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,
-.IR mpol=bind:0\-3,5,7,9\-15 .
-.SH VERSIONS
-The
-.B tmpfs
-facility was added in Linux 2.4, as a successor to the older
-.B ramfs
-facility, which did not provide limit checking or
-allow for the use of swap space.
-.SH NOTES
-In order for user-space tools and applications to create
-.B tmpfs
-filesystems, the kernel must be configured with the
-.B CONFIG_TMPFS
-option.
-.P
-The
-.B tmpfs
-filesystem supports extended attributes (see
-.BR xattr (7)),
-but
-.I user
-extended attributes are not permitted.
-.P
-An internal shared memory filesystem is used for
-System V shared memory
-.RB ( shmget (2))
-and shared anonymous mappings
-.RB ( mmap (2)
-with the
-.B MAP_SHARED
-and
-.B MAP_ANONYMOUS
-flags).
-This filesystem is available regardless of whether
-the kernel was configured with the
-.B CONFIG_TMPFS
-option.
-.P
-A
-.B tmpfs
-filesystem mounted at
-.I /dev/shm
-is used for the implementation of POSIX shared memory
-.RB ( shm_overview (7))
-and POSIX semaphores
-.RB ( sem_overview (7)).
-.P
-The amount of memory consumed by all
-.B tmpfs
-filesystems is shown in the
-.I Shmem
-field of
-.I /proc/meminfo
-and in the
-.I shared
-field displayed by
-.BR free (1).
-.P
-The
-.B tmpfs
-facility was formerly called
-.BR shmfs .
-.SH SEE ALSO
-.BR df (1),
-.BR du (1),
-.BR memfd_create (2),
-.BR mmap (2),
-.BR set_mempolicy (2),
-.BR shm_open (3),
-.BR mount (8)
-.P
-The kernel source files
-.I Documentation/filesystems/tmpfs.txt
-and
-.IR Documentation/admin\-guide/mm/transhuge.rst .