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 cur-
rently 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 separate size limits. /tmp is not required to be a tmpfs, but is
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 previ-
ously /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 RAMLOCK=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 compatibility 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 compatibil-
ity 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" suffix 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 hundreds 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@debian.org>
SEE ALSO
mount(8), rcS(5).
18 Feb 2012 tmpfs(5)