1TMPFS(5)                   Linux Programmer's Manual                  TMPFS(5)
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NAME

6       tmpfs - a virtual memory filesystem
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DESCRIPTION

9       The  tmpfs  facility  allows the creation of filesystems whose contents
10       reside in virtual memory.  Since the files on  such  filesystems  typi‐
11       cally reside in RAM, file access is extremely fast.
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13       The filesystem is automatically created when mounting a filesystem with
14       the type tmpfs via a command such as the following:
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16           $ sudo mount -t tmpfs -o size=10M tmpfs /mnt/mytmpfs
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18       A tmpfs filesystem has the following properties:
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20       *  The filesystem can employ swap space when physical  memory  pressure
21          demands it.
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23       *  The size option can be used to specify an upper limit on the size of
24          the filesystem.  (The default size is  half  of  the  available  RAM
25          size.)   The  filesystem  consumes  only as much physical memory and
26          swap space as is required to  store  the  current  contents  of  the
27          filesystem.
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29       *  During  a  remount operation (mount -o remount), the filesystem size
30          can be changed (without losing the existing contents of the filesys‐
31          tem).
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33       If a tmpfs filesystem is unmounted, its contents are discarded (lost).
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VERSIONS

36       The  tmpfs facility was added in Linux 2.4, as a successor to the older
37       ramfs facility, which did not provide limit checking or allow  for  the
38       use of swap space.
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NOTES

41       For a description of the mount options that may be employed when mount‐
42       ing a tmpfs filesystem, see mount(8).
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44       In order for user-space tools and applications to create tmpfs filesys‐
45       tems, the kernel must be configured with the CONFIG_TMPFS option.
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47       The  tmpfs  filesystem supports extended attributes (see xattr(7)), but
48       user extended attributes are not permitted.
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50       An internal shared memory filesystem is used for System V shared memory
51       (shmget(2))  and shared anonymous mappings (mmap(2) with the MAP_SHARED
52       and MAP_ANONYMOUS flags).  This filesystem is available  regardless  of
53       whether the kernel was configured with the CONFIG_TMPFS option.
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55       A  tmpfs  filesystem mounted at /dev/shm as used for the implementation
56       of  POSIX  shared  memory  (shm_overview(7))   and   POSIX   semaphores
57       (sem_overview(7)).
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59       The  amount of memory consumed by all tmpfs filesystems is shown in the
60       Shmem field of /proc/meminfo and  in  the  shared  field  displayed  by
61       free(1).
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63       The tmpfs facility was formerly called shmfs.
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SEE ALSO

66       df(1), du(1), memfd_create(2), mmap(2), shm_open(3), mount(8)
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68       The kernel source file Documentation/filesystems/tmpfs.txt.
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COLOPHON

71       This  page  is  part of release 4.15 of the Linux man-pages project.  A
72       description of the project, information about reporting bugs,  and  the
73       latest     version     of     this    page,    can    be    found    at
74       https://www.kernel.org/doc/man-pages/.
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78Linux                             2017-05-03                          TMPFS(5)