NAME
mount_tmpfs —
mount an efficient memory
file system
SYNOPSIS
mount_tmpfs |
[-g
group] [-m
mode] [-n
nodes] [-o
options]
[-s size]
[-u user]
tmpfs mount_point |
DESCRIPTION
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 reasonable maximum
given its size at mount time, which can be limited with
-s.
-
-
- -o
options
- Options are specified with a -o flag
followed by a comma-separated string of options. See the
mount(8) man page for
possible 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 (including 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
alternatively 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
kilobytes, a ‘M’ to indicate megabytes or a ‘G’ to
indicate gigabytes. Note that both lowercase and uppercase forms of these
letters are allowed.
EXAMPLES
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.
SEE ALSO
fstab(5),
mount(8)
HISTORY
The
mount_tmpfs utility first appeared in
NetBSD 4.0.
BUGS
File system meta-data is not pageable. If there is not enough main memory 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.