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
swap partitions.
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.
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 on startup.
- -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 unneeded
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
other use.
- -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.
- -d,
--daemon
- Run quietly in the background. This is the normal way to run the
program.
- -e,
--erase
- 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.
- -h,
--help
- 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 swap
space.
- -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 testing.
- -p [file],
--pidfile[=file]
- Write process identifier to file when starting (and delete
file when shutting down); defaults to
/var/lib/swapspace.pid.
- -P,
--paranoid
- 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.
- Caution
- 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 reboot.
- -q,
--quiet
- 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 space.
- -v,
--verbose
- Log debug information to system log and/or standard output, as
appropriate.
- -V,
--version
- 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
/var/lib/swapspace/
Written by Jeroen T. Vermeulen
Please report any bugs you may find on the project website at:
http://pqxx.org/development/swapspace/
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.