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 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 ALSO
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).
HISTORY
The
mount_mfs command appeared in
4.4BSD.
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.