MOUNT_MFS(8) BSD 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 specified 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 ALSOdisktab(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.
BSD December 8, 2007 BSD
