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I just ran df -h a minute ago and noticed a filesystem has been added that I'm not familiar with. Does anyone know why /run exists? Is this something that's been added by the kernel? By Arch Linux?

run              10M  236K  9.8M   3% /run
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Related: See the Debian /run release goal document, which includes details about how the change applies to 7.0+. wiki.debian.org/ReleaseGoals/RunDirectory – Zoredache May 28 '13 at 23:15
up vote 34 down vote accepted

Apparently, many tools (among them udev) will soon require a /run/ directory that is mounted early (as tmpfs). Arch developers introduced /run last month to prepare for this.

The udev runtime data moved from /dev/.udev/ to /run/udev/. The /run mountpoint is supposed to be a tmpfs mounted during early boot, available and writable to for all tools at any time during bootup, it replaces /var/run/, which should become a symlink some day. [1]

There is more detail here: http://www.h-online.com/open/news/item/Linux-distributions-to-include-run-directory-1219006.html

[1] From thread on the Arch Projects ML

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is it only for Arch or what ? /run will be add in RHEL/CentOs, Ubuntu ? – Rahul Patil Apr 7 '13 at 18:59

The /run directory is the companion directory to /var/run. Like for example /bin is the companion of /usr/bin.

That means that daemons like systemd and udev, which are started very early in the boot process - and perhaps before /var/run is available (i.e. mounted) - have with /run a standardized file system location available where they can store runtime information.

Like /bin contains important programs, which may be needed in the boot process before /usr is available (in case it is on its own filesystem).

The /run idea is a relatively new idea/standard, one supporter is the developer of systemd.

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Arch's /var/run directory is symlinked to /run. – Evan Teitelman Apr 20 '13 at 22:24
Debian's /var/run is also symlinked to /run – naoko Jan 16 at 14:04

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