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MOUNT_MFS(8) FreeBSD 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 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. FreeBSD 14.1-RELEASE-p8 September 12, 2016 FreeBSD 14.1-RELEASE-p8