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

NAME
     mount_mfs -- mount a memory based file system

SYNOPSIS
     mount_mfs [-N] [-a maxcontig] [-b block-size] [-d rotdelay] [-e maxbpg]
               [-f frag-size] [-g groupname] [-i bytes-per-inode]
               [-m free-space] [-n inodes] [-o options] [-p permissions]
               [-s size] [-u username] [-V verbose] special node

DESCRIPTION
     mount_mfs is used to build a file system in virtual memory and then mount
     it on a specified node.  mount_mfs exits and the contents of the file
     system are lost when the file system is unmounted.  If mount_mfs is sent
     a signal while running, for example during system shutdown, it will
     attempt to unmount its corresponding file system.  special is ignored.

     Options with numeric arguments may contain an optional (case-insensitive)
     suffix:
           b    Bytes; causes no modification.  (Default)
           k    Kilo; multiply the argument by 1024
           m    Mega; multiply the argument by 1048576
           g    Giga; multiply the argument by 1073741824

     The following options define the general layout policies:

     -N          Causes the memory file system parameters to be printed out
                 without really mounting the memory file system.

     -a maxcontig
                 This specifies the maximum number of contiguous blocks that
                 will be laid out before forcing a rotational delay (see the
                 -d option).  The default value is 8.  See tunefs(8) for more
                 details on how to set this option.

     -b block-size
                 The block size of the file system, in bytes.  It must be a
                 power of two.  The smallest allowable size is 4096 bytes.
                 The default size depends upon the size of the file system:

                       file system size  block-size
                       < 20 MB           4 KB
                       < 1024 MB         8 KB
                       >= 1024 MB        16 KB

     -d rotdelay
                 This specifies the expected time (in milliseconds) to service
                 a transfer completion interrupt and initiate a new transfer
                 on the same disk.  The default is 0 milliseconds.  See
                 tunefs(8) for more details on how to set this option.

     -e maxbpg   This indicates the maximum number of blocks any single file
                 can allocate out of a cylinder group before it is forced to
                 begin allocating blocks from another cylinder group.  The
                 default is about one quarter of the total blocks in a cylin-
                 der group.  See tunefs(8) for more details on how to set this
                 option.

     -f frag-size
                 The fragment size of the file system in bytes.  It must be a
                 power of two ranging in value between block-size/8 and
                 block-size.  The optimal block-size:frag-size ratio is 8:1.
                 Other ratios are possible, but are not recommended, and may
                 produce unpredictable results.  The default size depends upon
                 the size of the file system:

                       file system size  frag-size
                       < 20 MB           0.5 KB
                       < 1024 MB         1 KB
                       >= 1024 MB        2 KB

     -g groupname
                 This specifies the group name or group id of the root inode
                 of the file system.

     -i bytes-per-inode
                 This specifies the density of inodes in the file system.  If
                 fewer inodes are desired, a larger number should be used; to
                 create more inodes a smaller number should be given.  The
                 default is to create an inode for every (4 * frag-size) bytes
                 of data space:

                       file system size  bytes-per-inode
                       < 20 MB           2 KB
                       < 1024 MB         4 KB
                       >= 1024 MB        8 KB

     -m free-space
                 The percentage of space reserved from normal users; the mini-
                 mum free space threshold.  The default value used is 5%.  See
                 tunefs(8) for more details on how to set this option.

     -n inodes   This specifies the number of inodes for the filesystem.  If
                 both -i and -n are specified then -n takes precedence.

     -o          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.

     -p permissions
                 This specifies the permissions of the root inode of the file
                 system.

     -s size     The size of the file system in sectors.  An `s' suffix will
                 be interpreted as the number of sectors (the default).  All
                 other suffixes are interpreted as per other numeric argu-
                 ments, except that the number is converted into sectors by
                 dividing by the default sector size (which is 512 bytes)
                 after suffix interpretation.

     -u username
                 This specifies the user name or user id of the root inode of
                 the file system.

     -V verbose  This controls the amount of information written to stdout:
                       0    No output
                       1    Overall size and cylinder group details.
                       2    A progress bar (dots ending at right hand margin).
                       3    The first few super-block backup sector numbers
                            are displayed before the progress bar.
                       4    All the super-block backup sector numbers are dis-
                            played (no progress bar).
                 The default is 0.  If -N is specifed mount_mfs stops before
                 outputting the progress bar.

NOTES
     The owner and group ids of the root node of the new file system are set
     to the effective uid and gid of the user mounting the file system.

EXAMPLES
     Mount a 32 MB mfs on /tmp:

           mount_mfs -s 32m swap /tmp

SEE ALSO
     disktab(5), fs(5), disklabel(8), diskpart(8), dumpfs(8), fsck_ffs(8),
     fsirand(8), mount(8), newfs(8), tunefs(8)

     M. McKusick, W. Joy, S. Leffler, and R. Fabry, "A Fast File System for
     UNIX,", ACM Transactions on Computer Systems 2, 3, pp 181-197, August
     1984, (reprinted in the BSD System Manager's Manual).

HISTORY
     The mount_mfs command appeared in 4.2BSD.

BUGS
     The async mount(8) option is currently disabled in this file system
     because it causes hangs when writing lots of data.  The problem is that
     MFS needs to allocate pages to clean pages, so if it waits until the last
     minute to clean pages then there may not be any of them available to do
     the cleaning.

NetBSD 5.0_STABLE              December 8, 2007              NetBSD 5.0_STABLE
