今天為了測試方便，將登錄模式改成了init 3，發現居然無法登錄，用SSH連接正常，登錄後查了幾個日志後無果，後來打開Secure安全日志( less /var/log/secure)發現，有如下顯示：
Jul 27 19:02:29 oracle su: pam_unix(su-l:session): session closed for user root
Jul 28 09:28:20 oracle sshd[2611]: Server listening on :: port 22.
Jul 28 09:28:20 oracle sshd[2611]: error: Bind to port 22 on 0.0.0.0 failed: Address already in use.
Jul 28 09:28:49 oracle login: PAM unable to dlopen(/lib/security/pam_limits.so)
Jul 28 09:28:49 oracle login: PAM [error: /lib/security/pam_limits.so: wrong ELF class: ELFCLASS32]
Jul 28 09:28:49 oracle login: PAM adding faulty module: /lib/security/pam_limits.so
Jul 28 09:28:54 oracle login: pam_unix(login:session): session opened for user root by (uid=0)
Jul 28 09:28:54 oracle login: Module is unknown
Jul 28 09:28:57 oracle login: PAM unable to dlopen(/lib/security/pam_limits.so)
Jul 28 09:28:57 oracle login: PAM [error: /lib/security/pam_limits.so: wrong ELF class: ELFCLASS32]
Jul 28 09:28:57 oracle login: PAM adding faulty module: /lib/security/pam_limits.so
Jul 28 09:28:59 oracle login: pam_unix(login:session): session opened for user root by LOGIN(uid=0)
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Jul 28 09:28:59 oracle login: Module is unknown
Jul 28 09:29:04 oracle login: PAM unable to dlopen(/lib/security/pam_limits.so)
Jul 28 09:29:04 oracle login: PAM [error: /lib/security/pam_limits.so: wrong ELF class: ELFCLASS32]
Jul 28 09:29:04 oracle login: PAM adding faulty module: /lib/security/pam_limits.so
Jul 28 09:29:06 oracle login: pam_unix(login:auth): check pass; user unknown
Jul 28 09:29:06 oracle login: pam_unix(login:auth): authentication failure; logname=LOGIN uid=0 euid=0 tty=tty1 ruser= rhost=
Jul 28 09:29:06 oracle login: pam_succeed_if(login:auth): error retrieving information about user sys
Jul 28 09:29:08 oracle login: FAILED LOGIN 1 FROM (null) FOR sys, User not known to the underlying authentication module
Jul 28 09:29:38 oracle login: pam_unix(login:auth): authentication failure; logname=LOGIN uid=0 euid=0 tty=tty1 ruser= rhost= user=oracle
Jul 28 09:29:39 oracle login: FAILED LOGIN 2 FROM (null) FOR oracle, Authentication failure
Jul 28 09:29:48 oracle login: pam_unix(login:auth): authentication failure; logname=LOGIN uid=0 euid=0 tty=tty1 ruser= rhost= user=root
Jul 28 09:29:50 oracle login: FAILED LOGIN 3 FROM (null) FOR root, Authentication failure
Jul 28 09:30:03 oracle login: PAM unable to dlopen(/lib/security/pam_limits.so)
Jul 28 09:30:03 oracle login: PAM [error: /lib/security/pam_limits.so: wrong ELF class: ELFCLASS32]
Jul 28 09:30:03 oracle login: PAM adding faulty module: /lib/security/pam_limits.so
Jul 28 09:30:05 oracle login: pam_unix(login:auth): check pass; user unknown
Jul 28 09:30:05 oracle login: pam_unix(login:auth): authentication failure; logname= uid=0 euid=0 tty=tty2 ruser= rhost=
有提示/lib/security/pam_limits.so這個庫有問題，既然查找了一下find / -name pam_limits.so 發現有兩個一樣的庫文件：
[root@oracle ~]# find / -name pam_limits.so
/lib/security/pam_limits.so
/lib64/security/pam_limits.so
[root@oracle ~]#
由於我的系統是64位的CentOS，隨即將login裡面加載的庫文件給修改成64位庫中的文件：vi /etc/pam.d/login的最後一後修正為：session required /lib64/security/pam_limits.so
Reboot後在終端上登錄init 3進入字符界面一切正常！