1.\" $OpenBSD: mount_tmpfs.8,v 1.4 2014/11/16 02:22:10 brad Exp $ 2.\" $NetBSD: mount_tmpfs.8,v 1.14 2008/04/30 13:10:53 martin Exp $ 3.\" 4.\" Copyright (c) 2005, 2006 The NetBSD Foundation, Inc. 5.\" All rights reserved. 6.\" 7.\" This code is derived from software contributed to The NetBSD Foundation 8.\" by Julio M. Merino Vidal, developed as part of Google's Summer of Code 9.\" 2005 program. 10.\" 11.\" Redistribution and use in source and binary forms, with or without 12.\" modification, are permitted provided that the following conditions 13.\" are met: 14.\" 1. Redistributions of source code must retain the above copyright 15.\" notice, this list of conditions and the following disclaimer. 16.\" 2. Redistributions in binary form must reproduce the above copyright 17.\" notice, this list of conditions and the following disclaimer in the 18.\" documentation and/or other materials provided with the distribution. 19.\" 20.\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS 21.\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED 22.\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR 23.\" PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS 24.\" BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR 25.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF 26.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS 27.\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN 28.\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) 29.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 30.\" POSSIBILITY OF SUCH DAMAGE. 31.\" 32.Dd $Mdocdate: November 16 2014 $ 33.Dt MOUNT_TMPFS 8 34.Os 35.Sh NAME 36.Nm mount_tmpfs 37.Nd mount an efficient memory file system 38.Sh SYNOPSIS 39.Nm 40.Op Fl g Ar group 41.Op Fl m Ar mode 42.Op Fl n Ar nodes 43.Op Fl o Ar options 44.Op Fl s Ar size 45.Op Fl u Ar user 46.Ar tmpfs 47.Ar mount_point 48.Sh DESCRIPTION 49The 50.Nm 51command attaches an instance of the efficient memory file system to the 52global file system namespace. 53The 54.Ar tmpfs 55parameter only exists for compatibility with the other mount commands and 56is ignored. 57The directory specified by 58.Ar mount_point 59is converted to an absolute path before use and its attributes (owner, 60group and mode) are inherited unless explicitly overridden by the options 61described below. 62.Pp 63The following options are supported: 64.Bl -tag -width XoXoptions 65.It Fl g Ar group 66Specifies the group name or GID of the root inode of the file system. 67Defaults to the mount point's GID. 68.It Fl m Ar mode 69Specifies the mode (in octal notation) of the root inode of the file system. 70Defaults to the mount point's mode. 71.It Fl n Ar nodes 72Specifies the maximum number of nodes available to the file system. 73If not specified, the file system chooses a reasonable maximum given its 74size at mount time, which can be limited with 75.Fl s . 76.It Fl o Ar options 77Options are specified with a 78.Fl o 79flag followed by a comma-separated string of options. 80See the 81.Xr mount 8 82man page for possible options and their meanings. 83.It Fl s Ar size 84Specifies the total file system size in bytes. 85If zero is given (the default), the available amount of memory (including 86main memory and swap space) will be used. 87Note that four megabytes are always reserved for the system and cannot 88be assigned to the file system. 89.It Fl u Ar user 90Specifies the user name or UID of the root inode of the file system. 91Defaults to the mount point's UID. 92.El 93.Pp 94Every option that accepts a numerical value as its argument can take a 95trailing 96.Sq b 97to indicate bytes (the default), a 98.Sq k 99to indicate kilobytes, a 100.Sq M 101to indicate megabytes or a 102.Sq G 103to indicate gigabytes. 104Note that both lowercase and uppercase forms of these letters are allowed. 105.Sh EXAMPLES 106The following command mounts a tmpfs instance over the 107.Pa /tmp 108directory, inheriting its owner, group and mode settings: 109.Pp 110.Dl # mount -t tmpfs tmpfs /tmp 111.Pp 112The following command mounts a tmpfs instance over the 113.Pa /mnt 114directory, setting a 20 megabytes limit in space, owned by the 115.Sq joe 116user and belonging to the 117.Sq users 118group, with a restricted 0700 mode: 119.Pp 120.Dl # mount -t tmpfs -o -s20M -o -ujoe -o -gusers -o -m0700 tmpfs /mnt 121.Pp 122A corresponding 123.Xr fstab 5 124entry, using "swap" as a place holder: 125.Pp 126.Dl swap /mnt tmpfs rw,-s20M,-ujoe,-gusers,-m0700 0 0 127.Sh SEE ALSO 128.Xr fstab 5 , 129.Xr mount 8 130.Sh HISTORY 131The 132.Nm 133utility first appeared in 134.Nx 4.0 135and 136.Ox 5.5 . 137.Sh CAVEATS 138The update of mount options (through mount -u) is currently not supported. 139.Sh BUGS 140File system meta-data is not pageable. 141If there is not enough main memory to hold this information, the system may 142become unstable or very unresponsive because it will not be able to allocate 143required memory. 144A malicious user could trigger this condition if he could create lots of 145files inside a size-unbounded tmpfs file system. 146Limiting the number of nodes per file system 147.Pq Fl n 148will prevent this; the default value for this setting is also often adjusted 149to an adequate value to resolve this. 150