swapspace - dynamically manage swap space
Monitor memory and swap usage and allocate or deallocate swap space as
needed. This program aims to reduce or do away with the need for
swapspace can be built in two configurations: the full-featured one
(which is now the default) or the unconfigurable version. The latter
only accepts a few options, disabling all features that are probably
only relevant to developers. At some point in the feature, when enough
confidence exists that the various configuration parameters are either
good enough for everyone or have been made unnecessary, the
unconfigurable build may become the default.
The following options are accepted in the unconfigurable version. All
of these have more extensive equivalents in the full-featured version.
-d Quietly ignored; always enabled in unconfigurable version.
-e Attempt to free up all allocated swap files. Returns 0 if all
files were successfully erased, or 1 otherwise.
-h Display usage information and exit.
-p Write process identifier to /var/lib/swapspace.pid when starting
(and delete it when shutting down). The file’s name and
location cannot be changed in the unconfigurable version.
-q Quietly ignored; always enabled in unconfigurable version.
-v Quietly ignored; always enabled in unconfigurable version.
-V Print program version information and exit.
In most cases, these should be the only options of any interest for
normal use of the program. All files are kept in their default
locations, which were chosen in accordance with the Linux Filesystem
Hierarchy Standard, and algorithmic parameters are left at defaults
that have been tested to work well for a wide range of uses.
The full-featured configuration accepts more options, as listed below.
The long-format options may also be specified, without the leading
"--", in a configuration file. By default, /etc/swapspace.conf is read
-a duration, --cooldown=duration
If disk space runs out when allocating a swapfile, wait for
duration iterations (of roughly one second each) before
considering allocating one again; or if space doesn’t run out,
wait for duration iterations before considering deallocating
uneeded swapfiles. This stabilizes the daemon’s behaviour in
the face of varying memory requirements.
-B p, --buffer_elasticity=p
Consider p% of system-allocated I/O buffers to be available for
-c file, --configfile=file
Read file instead of the default configuration file.
-C p, --cache_elasticity=p
Consider p% of filesystem cache to be available for other use.
Run quietly in the background. This is the normal way to run
Attempt to free up all allocated swap files. Returns 0 if all
files were successfully erased, or 1 otherwise.
-f p, --freetarget=p
Aim to have p% of combined memory and swap space free.
Display usage information and exit.
-l p, --lower_freelimit=p
Try to keep at least p% of combined memory and swap space free;
if less than p percent is available, attempt to allocate more
-M size, --max_swapsize=size
Never let swapfiles become larger than size bytes. You don’t
normally need to set this; the daemon will learn when its swap
files get too big and adapt automatically.
-m size, --min_swapsize=size
Never bother to allocate any swapfiles smaller than size bytes.
There should be no need to change this variable except for
-p [file], --pidfile[=file]
Write process identifier to file when starting (and delete file
when shutting down); defaults to /var/lib/swapspace.pid.
Overwrite retired swapfiles before they are deleted, so an
attacker who obtains access to the disk without going through
the system’s access control checks (e.g. by unplugging the
computer and then rebooting from a CD) cannot retrieve the
swapped data. There is no guarantee that this will work, and it
will not thwart advanced forensic analysis using custom-built
hardware; but it may reduce the chances of an attacker with
physical access to the system obtaining passwords, credit card
numbers etc. The program will attempt to free up all allocated
swapfiles on termination and return a success code for this
cleanup, as if the --erase had been specified.
The --paranoid option will slow down swap file management
considerably. In particular, stopping the daemon will cause it
to try and deallocate (and wipe) all swapfiles it has created,
and they will not be available for swapping immediately after
Suppress informational output.
-s dir, --swappath=dir
Create swapfiles in directory dir instead of default location
/var/lib/swapspace. This location must be accessible to root
only; allowing anyone else to write to this directory or even
read swapped data would be a serious security breach.
-u p, --upper_freelimit=p
Avoid having more than p% of combined memory and swap space
free; if this percentage is exceeded, try to deallocate swap
Log debug information to system log and/or standard output, as
Print program version information and exit.
Numbers may be suffixed with k, m, g or t to indicate kilobytes,
megabytes, gigabytes or terabytes respectively: 1k means 1024 bytes, 1m
means 1024 kilobytes, 4g means 4096 megabytes and so on.
Timings are measured in iterations, which should typically last about
one second each. No pretense of accurate timing is made; this is not
the kind of program you would run on a hard-realtime system.
Any messages are sent to the system daemon log; it is also printed to
the standard output/error streams (as appropriate based on the urgency
of each individual message) if available.
State information can be logged by sending the program the SIGUSR1
signal (user-defined signal 1). Not all of this information will
always be current; most of the information internal to swapspace is
only updated when needed.
Sending the SIGUSR2 signal will make the program free all swapfiles
that are not currently needed, and abstain from allocating any more for
the timespan of one cooldown period. The program will behave as if it
just tried to create a swapfile but ran out of disk space.
/etc/init.d/swapspace /etc/swapspace.conf /usr/sbin/swapspace
Written by Jeroen T. Vermeulen
Please report any bugs you may find on the project website at:
Copyright © 2005 Software Industry Promotion Agency (SIPA), Thailand
This is free software; see the source for copying conditions. There is
no warranty whatsoever. Use entirely at your own risk.
kill(1), mkswap(8), signal(7), swapon(2), swapoff(2), swapon(8),