7.3.2 Cache Files

A cache file is a shell script that caches the results of configure tests run on one system so they can be shared between configure scripts and configure runs. It is not useful on other systems. If its contents are invalid for some reason, the user may delete or edit it.

By default, configure uses no cache file (technically, it uses `--cache-file=/dev/null'), to avoid problems caused by accidental use of stale cache files.

To enable caching, configure accepts `--config-cache' (or `-C') to cache results in the file `config.cache'. Alternatively, `--cache-file=file' specifies that file be the cache file. The cache file is created if it does not exist already. When configure calls configure scripts in subdirectories, it uses the `--cache-file' argument so that they share the same cache. See section 4.10 Configuring Other Packages in Subdirectories, for information on configuring subdirectories with the AC_CONFIG_SUBDIRS macro.

`config.status' only pays attention to the cache file if it is given the `--recheck' option, which makes it rerun configure.

It is wrong to try to distribute cache files for particular system types. There is too much room for error in doing that, and too much administrative overhead in maintaining them. For any features that can't be guessed automatically, use the standard method of the canonical system type and linking files (see section 11. Manual Configuration).

The site initialization script can specify a site-wide cache file to use, instead of the usual per-program cache. In this case, the cache file will gradually accumulate information whenever someone runs a new configure script. (Running configure merges the new cache results with the existing cache file.) This may cause problems, however, if the system configuration (e.g. the installed libraries or compilers) changes and the stale cache file is not deleted.