There are currently two methods to enabling PGP to cache passphrase's for an infinite amount of time. Both require launching PGP Agent.
1. ./pgp --cache-passphrase howard --passphrase password --passphrase-cache --passphrase-cache-timeout 0
2. Passphrase cache can be changed in the PGPprefs.xml. You need to modify two keys (seen below). If you set CLpassphraseCache to true and CLpassphraseCacheTimeout to 0 you can also create an infinite passphrase cache.
It does not matter which option you currently use. If you specify the timeout value to '0' you will note that you can only complete 65 - 100 cryptographic operations before the passphrase will be required again.
Symantec Corporation is committed to product quality and satisfied customers. This issue is currently being considered by Symantec Corporation to be addressed in a forthcoming version or Maintenance Pack of the product. Please be sure to refer back to this document periodically as any changes to the status of the issue will be reflected here.
Workaround: Currently if you change the value from 0 to a value like 31536000 (One full year in Seconds) we have found that the passphrase caching does work as intended.
This problem is occurring on all Supported Operating Systems that PGP command line can be installed on.