diff options
Diffstat (limited to 'man5/tmpfs.5')
| -rw-r--r-- | man5/tmpfs.5 | 271 |
1 files changed, 271 insertions, 0 deletions
diff --git a/man5/tmpfs.5 b/man5/tmpfs.5 new file mode 100644 index 0000000..8e4d063 --- /dev/null +++ b/man5/tmpfs.5 @@ -0,0 +1,271 @@ +.\" Copyright (c) 2016 by Michael Kerrisk <mtk.manpages@gmail.com> +.\" +.\" SPDX-License-Identifier: Linux-man-pages-copyleft +.\" +.TH tmpfs 5 2023-07-28 "Linux man-pages 6.05.01" +.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. +.PP +The filesystem is automatically created when mounting +a filesystem with the type +.B tmpfs +via a command such as the following: +.PP +.in +4n +.EX +$ sudo mount \-t tmpfs \-o size=10M tmpfs /mnt/mytmpfs +.EE +.in +.PP +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). +.PP +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. +.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. +.IP +Inodes may be specified with +.BR k , +.BR m , +or +.B g +suffixes like +.BR size , +but not a % suffix. +.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. +.PP +The +.B tmpfs +filesystem supports extended attributes (see +.BR xattr (7)), +but +.I user +extended attributes are not permitted. +.PP +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. +.PP +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)). +.PP +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). +.PP +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) +.PP +The kernel source files +.I Documentation/filesystems/tmpfs.txt +and +.IR Documentation/admin\-guide/mm/transhuge.rst . |