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NetBSD 6.1.5 - man page for mfs (netbsd section 8)

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

     mount_mfs -- mount a memory based file system

     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

     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 mount-
		 ing 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 comple-
		 tion 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
		 cylinder 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 rang-
		 ing 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 rec-
		 ommended, 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 minimum 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 separated string of
		 options.  See the mount(8) man page for possible 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 arguments, except that the number is converted into sectors by
		 dividing by the default sector size (which is 512 bytes) after suffix interpre-

     -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 displayed (no progress
		 The default is 0.  If -N is specified mount_mfs stops 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 4.2BSD.

     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 avail-
     able to do the cleaning.

BSD					 December 8, 2007				      BSD

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