mount_tmpfs(8) - NetBSD Manual Pages

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MOUNT_TMPFS(8)          NetBSD System Manager's Manual          MOUNT_TMPFS(8)


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 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.


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 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 7.0                       June 7, 2014                       NetBSD 7.0