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tmpfs(5) Debian Administrator's Manual tmpfs(5)

NAME
tmpfs - variables that configure tmpfs filesystems mounted during boot

DESCRIPTION
The /etc/default/tmpfs file contains variable settings in POSIX format:

VAR=VAL

Only one assignment is allowed per line. Comments (starting with '#') are also allowed.

This file is for the configuration of tmpfs filesystems mounted in early boot, before
filesystems from /etc/fstab are mounted. This currently includes the filesystems /run,
/run/lock, /run/shm and /tmp. /run is required to be a tmpfs on systems supporting tmpfs
mounts. /run/lock and /run/shm may be separate tmpfs mounts, useful for enforcing sepa‐
rate size limits. /tmp is not required to be a tmpfs, and is not mounted as a tmpfs by
default.

/run Previously configured using RAMRUN in /etc/default/rcS, /run is now always mounted
as a ram file system (tmpfs). The size of the tmpfs can be controlled using
TMPFS_SIZE and RUN_SIZE. If desired, the defaults may also be overridden with an
entry in in /etc/fstab, for example:

tmpfs /run tmpfs nodev,nosuid,size=10%,mode=755 0 0

The contents of /run will always be lost on system reboot, and it it is no longer
explicitly cleaned at boot. Packages can not expect directories in /run to exist
after boot. Packages expecting this are buggy and need to be fixed. Note that
/run was previously /var/run, and a compatibility symlink or bind mount will be
created to allow the old path to continue to function.

/run/lock
Previously configured using RAMLOCK in /etc/default/rcS. Configured using RAMLOCK,
TMPFS_SIZE and LOCK_SIZE. If desired, the defaults may also be overridden with an
entry in in /etc/fstab, for example:

tmpfs /run/lock tmpfs nodev,noexec,nosuid,size=52428800,mode=1777 0 0

Note that irrespective of these settings, /run/lock will be located on a tmpfs,
either one mounted on /run/lock (if RAMLOCK=yes) or one mounted on /run (if RAM‐
LOCK=no), and as a result the contents of /var/lock will always be lost on system
reboot, and it it is no longer explicitly cleaned at boot. Packages can not expect
directories in /var/lock to exist after boot. Packages expecting this are buggy
and need to be fixed. Note that /run/lock was previously /var/lock, and a compati‐
bility symlink or bind mount will be created to allow the old path to continue to
function.

/run/shm
Previously configured using RAMSHM in /etc/default/rcS. Note that the setting in
/etc/default/rcS, if present, will still be used, but the setting in
/etc/default/tmpfs will take precedence if enabled. Configured using RAMSHM,
TMPFS_SIZE and SHM_SIZE. If desired, the defaults may also be overridden with an
entry in in /etc/fstab, for example:

tmpfs /run/shm tmpfs nosuid,nodev,size=40%,mode=1777 0 0

Packages can not expect directories in /run/shm to exist after boot. Note that
/run/shm was previously /dev/shm, and a compatibility symlink or bind mount will be
created to allow the old path to continue to function. If an fstab entry for
/dev/shm exists instead of /run/shm, then /dev/shm will continue to be used; note
that this is only needed for users of newer versions of the Oracle database, which
contain a buggy check for /dev/shm.

/tmp Previously configured using RAMTMP in /etc/default/rcS. Note that the setting in
/etc/default/rcS, if present, will still be used, but the setting in
/etc/default/tmpfs will take precedence if enabled. Configured using RAMTMP,
TMPFS_SIZE and TMP_SIZE. If desired, the defaults may also be overridden with an
entry in in /etc/fstab, for example:

tmpfs /tmp tmpfs nodev,nosuid,size=20%,mode=1777 0 0

Packages can not expect directories in /tmp to exist after boot.

OPTIONS
The following variables can be set.

Enabling or disabling tmpfs mounts
The following options enable specific mounts (with the exception of /run) to be enabled or
disabled. Note that the addition of an entry to /etc/fstab for any of the following will
enable the mount unconditionally, overriding the setting here.

RAMLOCK
Mount /run/lock as a tmpfs (separately from /run). Defaults to yes; set to no to
disable (/run/lock will then be part of the /run tmpfs, if available).

RAMSHM Mount /run/shm as a tmpfs (separately from /run). Defaults to yes; set to no to
disable (/run/shm will then be part of the /run tmpfs, if available).

RAMTMP Mount /tmp as a tmpfs. Defaults to no; set to yes to enable (/tmp will be part of
the root filesystem if disabled). /tmp may also be configured to be a separate
mount in /etc/fstab, which will override the RAMTMP setting.

Configuring size limits for tmpfs mounts
The following options configure size limits for tmpfs mounts. Note that the addition of
an entry to /etc/fstab will override any of the limits specified here.

The following _SIZE variables are the maximum size (in bytes) that tmpfs filesystems can
use. The size will be rounded down to a multiple of the page size, 4096 bytes. If no
size is set, TMPFS_SIZE will be used as the default.

More complex mount options may be used by the creation of a suitable entry in /etc/fstab.
For example:

tmpfs /run tmpfs size=10% 0 0

is equivalent to

RUN_SIZE=10%

and will override the RUN_SIZE setting. This will allow additional options such as
nr_blocks and nr_inodes to be used, and also adjustment of the mode, nodev, nosuid, noexec
options should any change from the defaults be necessary.

TMPFS_SIZE
Maximum size for all tmpfs filesystems if no specific size is provided. The
default is 20%VM (20% of virtual memory, including swap space). If no value is
provided here, the kernel default (50% RAM) will be used. Note that the "%VM" suf‐
fix may be used in this and all the _SIZE settings below, but may not be used in
/etc/fstab (the absolute size is calculated by the init scripts).

RUN_SIZE
Maximum size of /run (was previously /var/run). The default is 10% core memory;
the size required varies widely depending upon the demands of the software being
run; this heuristic scales /run usage on system size. Samba in particular has been
seen to use at least 50MiB in a large heavily used server. Typical usage is hun‐
dreds of KiB, maximum is tens of MiB.

LOCK_SIZE
Maximum size of /run/lock (was previously /var/lock). Defaults to 5242880 (5 MiB).
Typical usage: tens of KiB; maximum hundreds of KiB. The default of 5 MiB should
ensure the limit is never reached.

SHM_SIZE
Maximum size of /run/shm (was previously /dev/shm). No default size; the size
required varies widely depending upon the demands of the software being run.

TMP_SIZE
Maximum size of /tmp. No default size.

Emergency overflow /tmp
If the amount of free space on the root filesystem falls below a certain size, a tmpfs
will be mounted on /tmp (irrespective of the RAMTMP setting, which this overrides). This
is to permit logins when there would otherwise be too little free space for this to be
possible.

TMP_OVERFLOW_LIMIT
Mount a tmpfs on /tmp if the amount of free space on the root filesystem is below
the specified limit at boot time (default 1024 KiB).

AUTHOR
Roger Leigh <rleigh AT debian.org>