SHA_CRYPT_MIN_ROUNDS (number) SHA_CRYPT_MAX_ROUNDS (number) When ENCRYPT_METHOD is set to SHA256 or SHA512, this defines the number of SHA rounds used by the encryption algorithm by default (when the number of rounds is not specified on the command line). With a lot of rounds, it is more difficult to brute forcing the password. But note also that more CPU resources will be needed to authenticate users. If not specified, the libc will choose the default number of rounds (5000), which is orders of magnitude too low for modern hardware. The values must be inside the 1000-999,999,999 range. If only one of the SHA_CRYPT_MIN_ROUNDS or SHA_CRYPT_MAX_ROUNDS values is set, then this value will be used. If SHA_CRYPT_MIN_ROUNDS > SHA_CRYPT_MAX_ROUNDS, the highest value will be used. Note: This only affect the generation of group passwords. The generation of user passwords is done by PAM and subject to the PAM configuration. It is recommended to set this variable consistently with the PAM configuration.