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tmpfs - variables that configure tmpfs filesystems mounted during boot

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 separate 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 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.
 
NOTE: This file is ignored when systemd is used as init system.
 

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