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TMPFS(5)                  FreeBSD File Formats Manual                 TMPFS(5)

NAME
     tmpfs - in-memory file system

SYNOPSIS
     To compile this driver into the kernel, place the following line in your
     kernel configuration file:

           options TMPFS

     Alternatively, to load the driver as a module at boot time, place the
     following line in loader.conf(5):

           tmpfs_load="YES"

DESCRIPTION
     The tmpfs driver implements an in-memory, or tmpfs file system.  The
     filesystem stores both file metadata and data in main memory.  This
     allows very fast and low latency accesses to the data.  The data is
     volatile.  An umount or system reboot invalidates it.  These properties
     make the filesystem's mounts suitable for fast scratch storage, like
     /tmp.

     If the system becomes low on memory and swap is configured (see swapon(8)
     ), the system can transfer file data to swap space, freeing memory for
     other needs.  Metadata, including the directory content, is never swapped
     out by the current implementation.  Keep this in mind when planning the
     mount limits, especially when expecting to place many small files on a
     tmpfs mount.

     When mmap(2) is used on a file from a tmpfs mount, the swap VM object
     managing the file pages is used to implement mapping and avoid double-
     copying of the file data.  This quirk causes process inspection tools,
     like procstat(1), to report anonymous memory mappings instead of file
     mappings.

OPTIONS
     The following options are available when mounting tmpfs file systems:

     gid                Specifies the group ID of the root inode of the file
                        system.  Defaults to the mount point's GID.

     uid                Specifies the user ID of the root inode of the file
                        system.  Defaults to the mount point's UID.

     mode               Specifies the mode (in octal notation) of the root
                        inode of the file system.  Defaults to the mount
                        point's mode.

     nonc               Do not use namecache to resolve names to files for the
                        created mount.  This saves memory, but currently might
                        impair scalability for highly used mounts on large
                        machines.

     inodes             Specifies the maximum number of nodes available to the
                        file system.  If not specified, the file system
                        chooses a reasonable maximum based on the file system
                        size, which can be limited with the size option.

     size               Specifies the total file system size in bytes.  If
                        zero (the default) or a value larger than SIZE_MAX -
                        PAGE_SIZE is given, the available amount of memory
                        (including main memory and swap space) will be used.

     maxfilesize        Specifies the maximum file size in bytes.  Defaults to
                        the maximum possible value.

EXAMPLES
     To mount a tmpfs memory file system:

           mount -t tmpfs tmpfs /tmp

SEE ALSO
     procstat(1), mmap(2), nmount(2), unmount(2), fstab(5), mdmfs(8),
     mount(8), swapinfo(8), swapon(8)

HISTORY
     The tmpfs driver first appeared in FreeBSD 7.0.

AUTHORS
     The tmpfs kernel implementation was written by Julio M. Merino Vidal
     <[email protected]> as a Google Summer of Code project.

     Rohit Jalan and others ported it from NetBSD to FreeBSD.

     This manual page was written by Xin LI <[email protected]>.

FreeBSD 11.1-RELEASE-p4        January 20, 2017        FreeBSD 11.1-RELEASE-p4
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