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MOUNT_TMPFS(8) NetBSD System Manager's Manual MOUNT_TMPFS(8)
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mount_tmpfs -- mount an efficient memory file system
mount_tmpfs [-g group] [-m mode] [-n nodes] [-o options] [-s size]
[-u user] tmpfs mount_point
The mount_tmpfs command attaches an instance of the efficient memory file
system to the global file system namespace. The tmpfs parameter only
exists for compatibility with the other mount commands and is ignored.
The directory specified by mount_point is converted to an absolute path
before use and its attributes (owner, group and mode) are inherited
unless explicitly overridden by the options described below.
The following options are supported:
-g group Specifies the group name or GID of the root inode of the file
system. Defaults to the mount point's GID.
-m mode Specifies the mode (in octal notation) of the root inode of
the file system. Defaults to the mount point's mode.
-n nodes Specifies the maximum number of nodes available to the file
system. If not specified, the file system chooses a reason-
able maximum given its size at mount time, which can be lim-
ited with -s.
-o options Options are specified with a -o flag followed by a comma-sep-
arated string of options. See the mount(8) man page for pos-
sible options and their meanings.
-s size Specifies the total file system size in bytes. If zero is
given (the default), the available amount of memory (includ-
ing main memory and swap space) will be used. Note that some
memory is always reserved for the system and cannot be
assigned to the file system. The exact amount depends on the
available memory and details of the kernel memory usage, it
might even change slightly during runtime. Size can alterna-
tively be specified as a percentage of the available system
ram by using the notation ram%n where n is a number between 1
and 100. Similarily it can be specified as a fraction of the
available system ram by using ram/n where n is the divisor.
(Using ram%25 and ram/4 will result in the same limit.)
-u user Specifies the user name or UID of the root inode of the file
system. Defaults to the mount point's UID.
Every option that accepts a numerical value as its argument can take a
trailing `b' to indicate bytes (the default), a `k' to indicate kilo-
bytes, a `M' to indicate megabytes or a `G' to indicate gigabytes. Note
that both lowercase and uppercase forms of these letters are allowed.
The following command mounts a tmpfs instance over the /tmp directory,
inheriting its owner, group and mode settings:
# mount -t tmpfs tmpfs /tmp
The following command mounts a tmpfs instance over the /mnt directory,
setting a 20 megabytes limit in space, owned by the `joe' user and
belonging to the `users' group, with a restricted 0700 mode:
# mount -t tmpfs -o -s20M -o -ujoe -o -gusers -o -m0700 tmpfs /mnt
See /usr/share/examples/fstab/fstab.ramdisk for some examples on how to
add tmpfs entries to /etc/fstab.
The mount_tmpfs utility first appeared in NetBSD 4.0.
File system meta-data is not pageable. If there is not enough main mem-
ory to hold this information, the system may become unstable or very
unresponsive because it will not be able to allocate required memory. A
malicious user could trigger this condition if he could create lots of
files inside a size-unbounded tmpfs file system. Limiting the number of
nodes per file system (-n) will prevent this; the default value for this
setting is also often adjusted to an adequate value to resolve this.
NetBSD 8.1 June 7, 2014 NetBSD 8.1