swapspace: Dynamically manage swap space

DESCRIPTION

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 swapfiles.

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 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 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 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 Userious 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.

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