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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. The parameters to mount_mfs are the same as those to newfs. If the -T flag is specified (see below), the special file is unused. Otherwise, it is only used to read the disk label which provides a set of configuration parameters for the memory based file system. The special file is typically that of the primary swap area, since that is where the file system will be backed up when free memory gets low and the memory supporting the file system has to be paged.

The following options define the general layout policies.

-N

Causes the file system parameters to be printed out without really creating the file system.

-O

Creates a 4.3BSD format filesystem. This options is primarily used to build root filesystems that can be understood by older boot ROMs.

-T

Uses information for the specified disk from /etc/disktab instead of trying to get the information from a disklabel.

-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 one. See tunefs(8) for more details on how to set this option.

-b block-size

The block size of the file system, in bytes.

-c #cylinders/group

The number of cylinders per cylinder group in a file system. The default value is 16.

-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 4 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.

-i number of bytes per inode

This specifies the density of inodes in the file system. The default is to create an inode for each 2048 bytes of data space. If fewer inodes are desired, a larger number should be used; to create more inodes a smaller number should be given.

-m free space %

The percentage of space reserved from normal users; the minimum free space threshold. The default value used is 10%. See tunefs(8) for more details on how to set this option.

-n rotational positions

Determines how many rotational time slots there are in one revolution of the disk.

-o optimization preference

(``space'' or ``time'') The file system can either be instructed to try to minimize the time spent allocating blocks, or to try to minimize the space fragmentation on the disk. If the value of minfree (see above) is less than 10%, the default is to optimize for space; if the value of minfree is greater than or equal to 10%, the default is to optimize for time. See tunefs(8) for more details on how to set this option.

-s size

The size of the file system in sectors.

The following options override the standard sizes for the disk geometry. Their default values are taken from the disk label. Changing these defaults is useful only when using newfs to build a file system whose raw image will eventually be used on a different type of disk than the one on which it is initially created (for example on a write-once disk). Note that changing any of these values from their defaults will make it impossible for fsck to find the alternate superblocks if the standard superblock is lost.

-S sector-size

The size of a sector in bytes (almost never anything but 512).

-k sector 0 skew, per track

Used to describe perturbations in the media format to compensate for a slow controller. Track skew is the offset of sector 0 on track N relative to sector 0 on track N-1 on the same cylinder.

-l hardware sector interleave

Used to describe perturbations in the media format to compensate for a slow controller. Interleave is physical sector interleave on each track, specified as the denominator of the ratio:

sectors read/sectors passed over

Thus an interleave of 1/1 implies contiguous layout, while 1/2 implies logical sector 0 is separated by one sector from logical sector 1.

-p spare sectors per track

Spare sectors (bad sector replacements) are physical sectors that occupy space at the end of each track. They are not counted as part of the sectors/track (-u) since they are not available to the file system for data allocation.

-r revolutions/minute

The speed of the disk in revolutions per minute.

-t #tracks/cylinder

The number of tracks/cylinder available for data allocation by the file system.

-u sectors/track

The number of sectors per track available for data allocation by the file system. This does not include sectors reserved at the end of each track for bad block replacement (see the -p option.)

-x spare sectors per cylinder

Spare sectors (bad sector replacements) are physical sectors that occupy space at the end of the last track in the cylinder. They are deducted from the sectors/track (-u) of the last track of each cylinder since they are not available to the file system for data allocation.

The options to the mount_mfs command are as described for the newfs command, except for the -o option.

That option is as follows:

-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.