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 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 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 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 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" 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).