mount_mfs —
mount a memory based file system
  
    | mount_mfs | [ -N] [-amaxcontig] [-bblock-size] [-drotdelay] [-emaxbpg] [-ffrag-size] [-ggroupname] [-ibytes-per-inode] [-mfree-space] [-ninodes] [-ooptions] [-ppermissions] [-ssize] [-uusername] [-Vverbose] special node | 
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.
- -amaxcontig
- This specifies the maximum number of contiguous blocks that will be laid
      out before forcing a rotational delay (see the -doption). The default value is 8. See
      tunefs(8) for more details
      on how to set this option.
- -bblock-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
 
 
- -drotdelay
- 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.
- -emaxbpg
- 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 cylinder group. See
      tunefs(8) for more details
      on how to set this option.
- -ffrag-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
 
 
- -ggroupname
- This specifies the group name or group id of the root inode of the file
      system.
- -ibytes-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
 
 
- -mfree-space
- The percentage of space reserved from normal users; the minimum free space
      threshold. The default value used is 5%. See
      tunefs(8) for more details
      on how to set this option.
- -ninodes
- This specifies the number of inodes for the filesystem. If both
      -iand-nare specified
      then-ntakes precedence.
- -o
- Options are specified with a -oflag followed by a
      comma separated string of options. See the
      mount(8) man page for
      possible options and their meanings.
- -ppermissions
- This specifies the permissions of the root inode of the file system.
- -ssize
- 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 arguments, except that the number is
      converted into sectors by dividing by the default sector size (which is
      512 bytes) after suffix interpretation.
- -uusername
- This specifies the user name or user id of the root inode of the file
      system.
- -Vverbose
- 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 displayed (no progress
          bar).
 
 The default is 0. If-Nis specifiedmount_mfsstops before outputting the progress
      bar.
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.
Mount a 32 MB mfs on /tmp:mount_mfs -s 32m swap
  /tmp
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).
The mount_mfs command appeared in
  4.4BSD.
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.