DragonFly On-Line Manual Pages


TMPFS(5)		 DragonFly File Formats Manual		      TMPFS(5)

NAME

tmpfs -- efficient memory file system

SYNOPSIS

To compile this driver into the kernel, place the following line in your kernel configuration file: options TMPFS Alternatively, to load the driver as a module at boot time, place the following line in loader.conf(5): tmpfs_load="YES"

OPTIONS

The following options are available when mounting tmpfs file systems: gid root group id. uid root user id. mode permissions in octal format. inodes maximum number of inodes. size maximum size for the file system. maxfilesize maximum file size of the file system.

DESCRIPTION

In the DragonFly implementation, tmpfs filesystems are backed by swap space. Only memory pressure will cause data to be backed to swap. Nor- mal filesystem operations such as fsync(), buffer cache flushing, and vnode recycling have no effect. tmpfs stores meta-data in wired kernel memory. Meta-data is not backed by swap so care must be taken if using tmpfs to store large numbers of small files. It is recommended that a large amount of swap space be reserved on modern DragonFly platforms to accommodate tmpfs and other subsystems. 32-bit kernels can accommodate 32G of swap by default while 64-bit kernels can accommodate 512G of swap by default. These defaults can be increased though it should be noted that 32-bit kernels are ultimately limited by the amount of KVM available in its small 32-bit address space. tmpfs will allocate and deallocate swap backing store on the fly based on usage. By default tmpfs allows up to 100% of swap space to be used. If this is not desirable then the size option should be used to limit its size. Every option that accepts a numerical value as its argument can take a trailing `b' to indicate bytes (the default), a trailing `k' to indicate kilobytes, a trailing `M' to indicate megabytes or a trailing `G' to indicate gigabytes. Note that both lowercase and uppercase forms of these letters are allowed.

EXAMPLES

To mount a tmpfs memory file system: mount -t tmpfs tmpfs /tmp

SEE ALSO

fstab(5), mount_nfs(8), mount_tmpfs(8), swapcache(8)

HISTORY

The tmpfs driver first appeared in DragonFly 2.5.

AUTHORS

The tmpfs kernel implementation was written by Julio M. Merino Vidal <jmmv@NetBSD.org> as a Google SoC project. Rohit Jalan and others ported it from NetBSD to FreeBSD. Naoya Sugioka and others ported it from NetBSD to DragonFly. This manual page was written by Xin LI <delphij@FreeBSD.org>.

BUGS

To mount NFS exported tmpfs DragonFly NFS client need to disable Read- dirPlus, see mount_nfs(8). DragonFly 3.9 February 2, 2010 DragonFly 3.9