Pluggable Authentication Modules (PAM) is a (not really) newer generic API for authentication originally proposed by Sun Microsystems in 1995 and adapted a year later on the Linux ecosystem. With an API change, don't expect things to keep the same name (nor to always map exactly the same).
Set a minimum password length of n characters. The default
value is 6. The maximum for DES crypt-based passwords is 8 characters.
Implementation can vary from distribution to distribution. On Ubuntu (like on Debian),
/etc/pam.d/passwd will source
/etc/pam.d/common-password where the first
password occurence includes the useful options. It can be altered and have an
minlen=X parameter added. This later file is autoregenerated by
pam-auth-update typically on upgrades, so check it works after an upgrade of PAM-related packages. Normally it should:
The script makes every effort to respect local changes to
/etc/pam.d/common-*. Local modifications to the list of module
options will be preserved, and additions of modules within the managed
portion of the stack will cause pam-auth-update to treat the
config files as locally modified and not make further changes to
the config files unless given the
Other options might still affect the result. Eg, if you set
obscure option will still reject a one-letter password as a palindrome, or a 2-letters password as too simple etc.
Be careful when altering PAM: you might lock yourself out of your system in case of wrong settings.