mount_memfs(1M)

mount_memfs -- mount memfs filesystems

Synopsis

mount [-F memfs] [generic_options] [-r] [-o specific_options]
[special|mount_point]
mount [-F memfs] [generic_options] [-r] [-o specific_options]
special mount_point mount- mount memfs filesystems

Description

generic_options are options supported by the generic mount command. mount attaches a memfs filesystem to the filesystem hierarchy at the pathname location mount_point, which must already exist. If mount_point has any contents prior to the mount operation, these remain hidden until the filesystem is once again unmounted.

The options are:

-F memfs

Specifies the memfs file system type

-o

Specifies memfs filesystem specific options in a comma-separated list. If invalid options are specified, a warning message is printed and the invalid options are ignored. Multiple filesystem-specific options may be listed in any order, but must be separated by commas. The following options are available:

swapmax: Maximum amount of memory, in bytes, this mounted filesystem is allowed to use. Default is the maximum value of an unsigned integer.
global_swapmax: Maximum amount of memory, in bytes, all memfs filesystems mounted without specifying 'swapmax' are allowed to use. Default is the maximum value of an unsigned integer.
rootmode: Specifies the mode of the root directory of the mounted file system. Default is 0775.

-r

Mount the filesystem read only.

Usage

The swapmax and global_swapmax options are mutually exclusive and cannot be specified on one command line (if they are, the command fails with EINVAL):

The swapmax option specifies memory to be used exclusively for the file system being mounted.
A file system mounted with swapmax ignores any global_swapmax established on previous mounts (for compatibility).
The global_swapmax option specifies memory to be used as a pool by all memfs file systems mounted without the swapmax option.
A file system mounted without swapmax, or without either option, shares the currently defined global_swapmax memory pool.
The initial value of global_swapmax on initial system installation is infinity (in order to be compatible with currently installed systems).
When a memfs mount is initiated specifying a new global_swapmax, then either:
- the mount will fail (returning EBUSY) if the new value of global_swapmax is less than the total space occupied by all currently mounted memfs file systems, or
- the mount will succeed and replace the current value of global_swapmax with the new value.

The global_swapmax option allows memfs file systems (like /var/tmp and /tmp) to share the same memory pool, and both:

reduce the overall amount of memory consumed by memfs file systems
allow temporary file systems to grow and shrink within a greater amount of memory than would be available to them individually by using the swapmax option

Files

/etc/mnttab: mount table

References

mkdir(2), mnttab(4), generic mount(1M), mount(2), open(2), umount(2)

Notices

If the directory on which a filesystem is to be mounted is a symbolic link, the filesystem is mounted on the directory to which the symbolic link refers, rather than on top of the symbolic link itself.

mount_memfs will set the root mode's owner and group information to bin, effectively doing a chown and chgrp.

Mounting an memfs filesystem creates an instantiation of the filesystem. Therefore, there is no corresponding mkfs command required for the memfs filesystem type.