[root@ok ~]# vim /etc/pam.d/su

   #%PAM-1.0

   auth            sufficient      pam_rootok.so

   # Uncomment the following line to implicitly trust users in the "wheel" group.

   #auth           sufficient      pam_wheel.so trust use_uid

   # Uncomment the following line to require a user to be in the "wheel" group.

   #auth           required        pam_wheel.so use_uid

   auth            include         system-auth

   account         sufficient      pam_succeed_if.so uid =  use_uid quiet

   account         include         system-auth

  password        include         system-auth

  session         include         system-auth

  session         optional        pam_xauth.so

将第４行的#号去掉，然后将登陆用户加入 wheel组

[root@ok ok]# usermod -G wheel ok

[ok@ok ~]$ su

[root@ok ok]#

su直接切换成root