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Filesystem manual pages describe drivers, not formats; except for fs, which describes the structures of ffs/ufs, not how to use it in the system. Reported by: emaste Reviewed by: des, imp, meena (previous version) Pull Request: https://github.com/freebsd/freebsd-src/pull/1077
230 lines
7.4 KiB
Groff
230 lines
7.4 KiB
Groff
.\"-
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.\" Copyright (c) 2007 Xin LI
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.\" Copyright (c) 2017 The FreeBSD Foundation, Inc.
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.\"
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.\" Part of this documentation was written by
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.\" Konstantin Belousov <kib@FreeBSD.org> under sponsorship
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.\" from the FreeBSD Foundation.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\"
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.\" THIS DOCUMENTATION IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
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.\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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.\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
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.\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
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.\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
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.\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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.\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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.\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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.\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
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.\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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.\"
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.\"-
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.\" Copyright (c) 2005, 2006 The NetBSD Foundation, Inc.
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.\" All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
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.\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
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.\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
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.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
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.\" BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
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.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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.\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
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.\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
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.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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.\" POSSIBILITY OF SUCH DAMAGE.
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.\"
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.Dd September 18, 2023
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.Dt TMPFS 4
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.Os
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.Sh NAME
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.Nm tmpfs
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.Nd "in-memory file system"
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.Sh SYNOPSIS
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To compile this driver into the kernel,
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place the following line in your
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kernel configuration file:
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.Bd -ragged -offset indent
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.Cd "options TMPFS"
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.Ed
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.Pp
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Alternatively, to load the driver as a
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module at boot time, place the following line in
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.Xr loader.conf 5 :
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.Bd -literal -offset indent
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tmpfs_load="YES"
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.Ed
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.Sh DESCRIPTION
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The
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.Nm
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driver implements an in-memory, or
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.Nm
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file system.
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The filesystem stores both file metadata and data in main memory.
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This allows very fast and low latency accesses to the data.
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The data is volatile.
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An umount or system reboot invalidates it.
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These properties make the filesystem's mounts suitable for fast
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scratch storage, like
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.Pa /tmp .
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.Pp
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If the system becomes low on memory and swap is configured
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.Po see
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.Xr swapon 8 Pc ,
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the system can transfer file data to swap space, freeing memory
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for other needs.
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Metadata, including the directory content, is never swapped out by the
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current implementation.
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Keep this in mind when planning the mount limits, especially when expecting
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to place many small files on a tmpfs mount.
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.Pp
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When
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.Xr mmap 2
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is used on a file from a tmpfs mount, the swap VM object managing the
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file pages is used to implement mapping and avoid double-copying of
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the file data.
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This quirk causes process inspection tools, like
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.Xr procstat 1 ,
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to report anonymous memory mappings instead of file mappings.
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.Sh OPTIONS
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The following options are available when
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mounting
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.Nm
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file systems:
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.Bl -tag -width "maxfilesize"
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.It Cm easize
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Set the maximum memory size used by extended attributes in bytes.
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The default is 16 megabytes.
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.It Cm export
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Accept the
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.Cm export
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option for compatibility with
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.Xr nfsv4 4 .
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This option does nothing.
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.It Cm gid
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Set the group ID of the root inode of the file system.
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The default is the mount point's GID.
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.It Cm inodes
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Set the maximum number of nodes available to the file system.
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If not specified, the file system chooses a reasonable maximum based on
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the file system size, which can be limited with the
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.Cm size
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option.
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.It Cm maxfilesize
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Set the maximum file size in bytes.
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The default is the maximum possible value.
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.It Cm mode
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Set the mode (in octal notation) of the root inode of the file system.
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The default is the mount point's mode.
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.It Cm nomtime
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Disable the tracking of mtime updates caused by writes to the
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shared mapped areas backed by
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.Nm
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files.
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This option removes periodic scans,
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which downgrade read-write-mapped pages to read-only to note the writes.
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.It Cm nonc
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Do not use namecache to resolve names to files for the created mount.
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This saves memory, but currently might impair scalability for highly
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used mounts on large machines.
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.It Cm nosymfollow
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Do not follow
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.Xr symlink 7 Ap s
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on the mounted file system.
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.It Cm pgread
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Enable pgcache read for the mount.
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.It Cm size
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Set the total file system size in bytes, unless suffixed
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with one of k, m, g, t, or p, which denote byte, kilobyte,
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megabyte, gigabyte, terabyte and petabyte respectively.
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If zero (the default) or a value larger than SIZE_MAX - PAGE_SIZE
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is given, the available amount of memory (including
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main memory and swap space) will be used.
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.It Cm uid
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Set the user ID of the root inode of the file system.
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The default is the mount point's UID.
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.It Cm union
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Refer to
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.Xr mount 8 .
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.El
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.Sh SYSCTL VARIABLES
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The following
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.Xr sysctl 8
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variables are available:
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.Bl -tag -width indent
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.It Va vfs.tmpfs.memory_percent
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The percentage of memory plus swap space available at kernel file system
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initialization that can be used by a file system with a size of 0.
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When this amount of space in use is reached, new files cannot be created
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and files cannot be extended.
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The default is 95%.
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Changing this value also changes
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.Va vfs.tmpfs.memory_reserved .
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.It Va vfs.tmpfs.memory_reserved
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The currently-reserved amount of memory plus swap space
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based on the memory percentage.
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The minimum is compiled into the system, and defaults to 4 MB.
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.El
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.Sh EXAMPLES
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Mount a
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.Nm
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memory file system:
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.Pp
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.Dl "mount -t tmpfs tmpfs /tmp"
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.Pp
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Configure a
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.Nm
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mount via
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.Xr fstab 5 :
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.Bd -literal -offset indent
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tmpfs /tmp tmpfs rw 0 0
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.Ed
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.Sh SEE ALSO
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.Xr procstat 1 ,
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.Xr mmap 2 ,
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.Xr nmount 2 ,
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.Xr unmount 2 ,
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.Xr fstab 5 ,
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.Xr mdmfs 8 ,
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.Xr mount 8 ,
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.Xr swapinfo 8 ,
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.Xr swapon 8
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.Sh HISTORY
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The
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.Nm
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driver first appeared in
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.Fx 7.0 .
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.Sh AUTHORS
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.An -nosplit
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The
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.Nm
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kernel implementation was written by
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.An Julio M. Merino Vidal Aq Mt jmmv@NetBSD.org
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as a Google Summer of Code project.
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.Pp
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.An Rohit Jalan
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and others ported it from
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.Nx
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to
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.Fx .
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.Pp
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This manual page was written by
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.An Xin LI Aq Mt delphij@FreeBSD.org .
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