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
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 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
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).
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
mounting a tmpfs filesystem, see mount(8).
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 as 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.
df(1), du(1), memfd_create(2), mmap(2), shm_open(3), mount(8)
The kernel source file Documentation/filesystems/tmpfs.txt.
This page is part of release 4.12 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 2017-05-03 TMPFS(5)
Pages that refer to this page: fallocate(2), ioctl_userfaultfd(2), lseek(2), madvise(2), memfd_create(2), mmap(2), remap_file_pages(2), swapon(2), shm_open(3), filesystems(5), proc(5), cgroups(7), keyrings(7), user_namespaces(7)