You can use the cache access list to make Squid never cache any response:
cache deny all
With Squid-2.7, Squid-3.1 and later you can also remove all ‘cache_dir’ options from your squid.conf to avoid having a cache directory.
With Squid-2.4, 2.5, 2.6, and 3.0 you need to use the “null” storage module:
cache_dir null /tmp
Note: a null cache_dir does not disable caching, but it does save you from creating a cache structure if you have disabled caching with cache. The directory (e.g., /tmp) must exist so that squid can chdir to it, unless you also use the coredump_dir option.
To configure Squid for the “null” storage module, specify it on the configure command line: