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 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 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 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 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 displayed (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)
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.