PAM: Pluggable authentication module is a system to authenticate users in several ways. PAM can use biometrics, ssh key passphrases, and other systems to authenticate users.
pam controls login behavior, an error in configuration may result in being locked out of your account. Test login behavior on alternate tty consoles before relying upon changes made, and make sure to have rescue media available.
Currently the following files are installed by pambase:
/etc/pam.d/login /etc/pam.d/passwd /etc/pam.d/su /etc/pam.d/system-auth /etc/pam.d/system-login /etc/pam.d/system-local-login /etc/pam.d/system-remote-login /etc/pam.d/system-services /etc/pam.d/other
The files starting with 'system' prefix are intended to be used by other PAM files. In particular:
- system-auth is used whenever user authentication is desired. It is included in PAM files for account manipulation tools (passwd, chsh, ...), authenticated daemons (imap, pop3), xscreensaver (for screen locking) and system-login.
- system-login is used whenever login is done. It is currently included only in system-local-login and system-remote-login.
- system-local-login is used whenever local system login is performed. It is used by login and display managers.
- system-remote-login is used whenever remote system login is performed. It is used by sshd.
- system-services is used whenever system daemons are started. It is used by start-stop-daemon and systemd.
How files are generated
The pambase Makefile generates the above files using traditional C preprocessor on top of templates. The preprocessor is provided with defines matching USE flags of choice. The processed files are then installed to user systems.
Problems with the current system
The problems with the current system are:
- centralised management of PAM backends,
- no easy way for user to modify the configuration files without having to repeatedly handle updates.
In particular, the ability to change authentication backends is very limited. If a new backend is to be supported out-of-the-box, one needs to update the pambase package and add more flags and conditionals to it. There is no sane way of controlling the module use order or adding out-of-tree PAM modules.
If user modifies module configuration, they need to maintain the modifications while pambase upgrades try to restore configuration files to original content.
ssh key auth
this might break login to users without ssh keys.
PAM can be used as an alternative to Keychain. Make sure you have a ssh key with a passphrase before enabling the pam ssh backend.
root # echo "sys-auth/pambase pam_ssh" >> /etc/portage/package.use/pambase root # emerge -1 sys-auth/pambase