Copyright (c) 2007 Xin LI
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$FreeBSD: stable/10/share/man/man5/tmpfs.5 316237 2017-03-30 05:57:44Z ngie $
.Dd January 20, 2017 .Dt TMPFS 5 .Os .Sh NAME .Nm tmpfs .Nd "in-memory file system" .Sh SYNOPSIS To compile this driver into the kernel, place the following line in your kernel configuration file: d -ragged -offset indent .Cd "options TMPFS" .Ed
p Alternatively, to load the driver as a module at boot time, place the following line in .Xr loader.conf 5 : d -literal -offset indent tmpfs_load="YES" .Ed .Sh DESCRIPTION The .Nm driver implements an in-memory, or .Tn tmpfs file system. The filesystem stores both file metadata and data in main memory. This allows very fast and low latency accesses to the data. The data is volatile. An umount or system reboot invalidates it. These properties make the filesystem's mounts suitable for fast scratch storage, like
a /tmp .
p If the system becomes low on memory and swap is configured (see .Xr swapon 8 ), the system can transfer file data to swap space, freeing memory for other needs. Metadata, including the directory content, is never swapped out by the current implementation. Keep this in mind when planning the mount limits, especially when expecting to place many small files on a tmpfs mount.
p When .Xr mmap 2 is used on a file from a tmpfs mount, the swap VM object managing the file pages is used to implement mapping and avoid double-copying of the file data. This quirk causes process inspection tools, like .Xr procstat 1 , to report anonymous memory mappings instead of file mappings. .Sh OPTIONS The following options are available when mounting .Nm file systems: l -tag -width "It Cm maxfilesize" t Cm gid Specifies the group ID of the root inode of the file system. Defaults to the mount point's GID. t Cm uid Specifies the user ID of the root inode of the file system. Defaults to the mount point's UID. t Cm mode Specifies the mode (in octal notation) of the root inode of the file system. Defaults to the mount point's mode. t Cm nonc Do not use namecache to resolve names to files for the created mount. This saves memory, but currently might impair scalability for highly used mounts on large machines. t Cm inodes Specifies the maximum number of nodes available to the file system. If not specified, the file system chooses a reasonable maximum based on the file system size, which can be limited with the .Cm size option. t Cm size Specifies the total file system size in bytes. If zero (the default) or a value larger than SIZE_MAX - PAGE_SIZE is given, the available amount of memory (including main memory and swap space) will be used. t Cm maxfilesize Specifies the maximum file size in bytes. Defaults to the maximum possible value. .El .Sh EXAMPLES To mount a .Nm memory file system:
p .Dl "mount -t tmpfs tmpfs /tmp" .Sh SEE ALSO .Xr procstat 1 , .Xr mmap 2 , .Xr nmount 2 , .Xr unmount 2 , .Xr fstab 5 , .Xr mdmfs 8 , .Xr mount 8 , .Xr swapinfo 8 , .Xr swapon 8 .Sh HISTORY The .Nm driver first appeared in .Fx 7.0 . .Sh AUTHORS .An -nosplit The .Nm kernel implementation was written by .An Julio M. Merino Vidal Aq jmmv@NetBSD.org as a Google Summer of Code project.
p .An Rohit Jalan and others ported it from .Nx to .Fx .
p This manual page was written by .An Xin LI Aq delphij@FreeBSD.org .