Section: Linux-PAM Manual (8)
In the case of the su?(1) application the historical usage is to permit the superuser to adopt the identity of a lesser user without the use of a password. To obtain this behavior with PAM the following pair of lines are needed for the corresponding entry in the /etc/pam.d/su configuration file:
# su authentication. Root is granted access by default. auth sufficient pam_rootok.so auth required pam_unix.so
pam_rootok was written by Andrew G. Morgan, <firstname.lastname@example.org>.
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