Provided by:
passwd_4.1.4.2+svn3283-3ubuntu5_i386 
CONFIGURATION
The following configuration variables in /etc/login.defs change the
behavior of this tool:
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).
The values must be inside the 1000-999999999 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.
/etc/passwd
/etc/shadow
/etc/login.defs
/etc/pam.d/chpasswd
PAM configuration for chpasswd.
passwd(1), newusers(8), login.defs(5), useradd(8).
04/09/2012 chpasswd(8)