CentOS 7以前的版本                                                          

修改 /etc/inittab 檔案，將“id:5:initdefault:”這一行的"id:"後的數字（預設為5）改為 3即可。

Linux將X-Window（簡稱X）僅僅視作一個程式，而不捆綁於其核心之中。在UNIX/Linux中一般將執行級別分為7級（一說九級，但實際應用為六級，保留一級）：

0 系統停機
1 單使用者模式
2 多使用者模式
3 網路多使用者模式
4 保留
5 X11模式（即進入圖形介面模式）
6 重起

要想修改Linux開機的啟動模式（控制檯或圖形介面等），只需修改/etc/inittab檔案。

/etc/inittab檔案（部分）：
# Default runlevel. The runlevels used by RHS are:
# 0 - halt (Do NOT set initdefault to this)
# 1 - Single user mode
# 2 - Multiuser, without NFS (The same as 3, if you do not have networking)
# 3 - Full multiuser mode
# 4 - unused
# 5 - X11
# 6 - reboot (Do NOT set initdefault to this)
#
id:5:initdefault:

要想修改啟動級別，將“id:5:initdefault:”這一行的"id:"後的數字（預設為5）改為你要的級別即可。

注意：不要改為0，0表示關機；也不要改為6，否則開機就不停的重啟了~  

CentOS 7版本改為以下的方法                                              

cat /etc/inittab 內容變為如下
# inittab is no longer used when using systemd. #
# ADDING CONFIGURATION HERE WILL HAVE NO EFFECT ON YOUR SYSTEM.
#
# Ctrl-Alt-Delete is handled by /etc/systemd/system/ctrl-alt-del.target
#
# systemd uses 'targets' instead of runlevels. By default, there are two main targets:
#
# multi-user.target: analogous to runlevel 3
# graphical.target: analogous to runlevel 5
#
# To set a default target, run:
#
# ln -sf /lib/systemd/system/<target name>.target /etc/systemd/system/default.target
#
[

[email protected] ~]# cat /etc/systemd/system/default.target
#  This file is part of systemd.
#
#  systemd is free software; you can redistribute it and/or modify it
#  under the terms of the GNU Lesser General Public License as published by
#  the Free Software Foundation; either version 2.1 of the License, or
#  (at your option) any later version.

就是說要用

ln -sf /lib/systemd/system/multi-user.target /etc/systemd/system/default.target

或者

預設執行級別3：systemctl set-default multi-user.target

預設執行級別5：systemctl set-default graphical.target

但是用SSH可以登入，檢視日誌 tail -n 50 /var/log/secure

Aug 14 21:37:00 localhost login: Module is unknown
Aug 14 21:37:08 localhost login: PAM unable to dlopen(/lib/security/pam_limits.so): /lib/security/pam_limits.so: cannot open shared object file: No such file or directory
Aug 14 21:37:08 localhost login: PAM adding faulty module: /lib/security/pam_limits.so
Aug 14 21:37:12 localhost login: pam_unix(login:session): session opened for user oracle by LOGIN(uid=0)

再看登入驗證檔案 cat /etc/pam.d/login

發現是使用了32位的驗證檔案，改為64位的就可以了

#%PAM-1.0
auth [user_unknown=ignore success=ok ignore=ignore default=bad] pam_securetty.so
auth       substack     system-auth
auth       include      postlogin
account    required     pam_nologin.so
account    include      system-auth
password   include      system-auth
# pam_selinux.so close should be the first session rule
session    required     pam_selinux.so close
session    required     pam_loginuid.so
session    optional     pam_console.so
# pam_selinux.so open should only be followed by sessions to be executed in the user context
session    required     pam_selinux.so open
session    required     pam_namespace.so
session    optional     pam_keyinit.so force revoke
session    include      system-auth
session    include      postlogin
-session   optional     pam_ck_connector.so

session    required     /lib/security/pam_limits.so    ⇒　/lib64/security/pam_limits.so
session    required     pam_limits.so

儲存後重啟啟動，OK！