Occasionally, a NetHack game will be interrupted by disaster
when the game or the system crashes.
Prior to NetHack v3.1, these games were lost because various information
like the players inventory was kept only in memory.
Now, all pertinent information can be written out to disk,
so such games can be recovered at the point of the last level change.
base options tell
recover which files to process.
Each base option specifies recovery of a separate game.
-d option, which must be the first argument if it appears,
supplies a directory which is the NetHack playground.
It overrides the value from NETHACKDIR, HACKDIR, or the directory
specified by the game administrator during compilation
For recovery to be possible,
nethack must have been compiled with the INSURANCE option, and the run-time option
checkpoint must also have been on.
NetHack normally writes out files for levels as the player leaves them,
so they will be ready for return visits.
When checkpointing, NetHack also writes out the level entered and
the current game state on every level change.
This naturally slows level changes down somewhat.
The level file names are of the form base.nn, where nn is an internal
bookkeeping number for the level.
The file base.0 is used for game identity, locking, and, when checkpointing,
for the game state.
Various OSes use different strategies for constructing the base name.
Microcomputers use the character name, possibly truncated and modified
to be a legal filename on that system.
Multi-user systems use the (modified) character name prefixed
by a user number to avoid conflicts,
or "xlock" if the number of concurrent players is being limited.
It may be necessary to look in the playground to find the correct
base name of the interrupted game.
recover will transform these level files into a save file of the same name as
nethack would have used.
recover must be able to read and delete files from the playground
and create files in the save directory,
it has interesting interactions with game security.
Giving ordinary players access to
recover through setuid or setgid is tantamount to leaving the playground
with respect to both cheating and messing up other players.
For a single-user system, this of course does not change anything,
so some of the microcomputer ports install
recover by default.
For a multi-user system,
the game administrator may want to arrange for all .0 files in the
playground to be fed to recover when the host machine boots,
and handle game crashes individually.
If the user population is sufficiently trustworthy,
recover can be installed with the same permissions the
nethack executable has.
In either case,
recover is easily compiled from the distribution utility directory.