我的测试平台为：
CentOS 6.5 x86 32位 桌面版（GDM）
[root@localhost ~]# cat /etc/issue
CentOS release 6.5 (Final)
Kernel \r on an \m
从搜索上搜到的都是修改/etc/gdm/custom.conf文件，如果你按照搜到的去修改（/etc/gdm/custom.conf）的话，重新启动后，普通用户并不能实现自动登陆。
经我测试及查看代码发现，CentOS 6.5 并非修改此文件，而是修改/etc/gdm/gdm.schemas 这个文件。
我的修改此文件，将普通用户leekwen实现自动登陆，修改后与修改前的对比做出了patch文件。
参见patch代码：
[root@localhost ~]# cat /etc/gdm/gdm.patch
--- gdm.schemas.bak 2016-12-6 9:30:26.047999810 +0800
+++ gdm.schemas 2016-12-6 9:44:40.213279864 +0800
@@ -25,22 +25,22 @@
<schema>
<key>daemon/AutomaticLoginEnable</key>
<signature>b</signature>
- <default>false</default>
+ <default>true</default>
</schema>
<schema>
<key>daemon/AutomaticLogin</key>
<signature>s</signature>
- <default></default>
+ <default>leekwen</default>
</schema>
<schema>
<key>daemon/TimedLoginEnable</key>
<signature>b</signature>
- <default>false</default>
+ <default>true</default>
</schema>
<schema>
<key>daemon/TimedLogin</key>
<signature>s</signature>
- <default></default>
+ <default>leekwen</default>
</schema>
<schema>
<key>daemon/TimedLoginDelay</key>
@@ -51,7 +51,7 @@
<schema>
<key>debug/Enable</key>
<signature>b</signature>
- <default>false</default>
+ <default>true</default>
</schema>
<schema>
修改后，完成的文件如下：
[root@localhost ~]# cat /etc/gdm/gdm.schemas
<gdmschemafile>
<schemalist>
<schema>
<key>chooser/Multicast</key>
<signature>b</signature>
<default>false</default>
</schema>
<schema>
<key>chooser/MulticastAddr</key>
<signature>s</signature>
<default>ff02::1</default>
</schema>
<schema>
<key>daemon/User</key>
<signature>s</signature>
<default>gdm</default>
</schema>
<schema>
<key>daemon/Group</key>
<signature>s</signature>
<default>gdm</default>
</schema>
<schema>
<key>daemon/AutomaticLoginEnable</key>
<signature>b</signature>
<default>true</default>
</schema>
<schema>
<key>daemon/AutomaticLogin</key>
<signature>s</signature>
<default>leekwen</default>
</schema>
<schema>
<key>daemon/TimedLoginEnable</key>
<signature>b</signature>
<default>true</default>
</schema>
<schema>
<key>daemon/TimedLogin</key>
<signature>s</signature>
<default>leekwen</default>
</schema>
<schema>
<key>daemon/TimedLoginDelay</key>
<signature>i</signature>
<default>30</default>
</schema>
<schema>
<key>debug/Enable</key>
<signature>b</signature>
<default>true</default>
</schema>
<schema>
<key>security/DisallowTCP</key>
<signature>b</signature>
<default>true</default>
</schema>
<schema>
<key>greeter/Include</key>
<signature>s</signature>
<default></default>
</schema>
<schema>
<key>greeter/Exclude</key>
<signature>s</signature>
<default>bin,root,daemon,adm,lp,sync,shutdown,halt,mail,news,uucp,operator,nobody,nobody4,noaccess,postgres,pvm,rpm,nfsnobody,pcap</default>
</schema>
<schema>
<key>greeter/IncludeAll</key>
<signature>b</signature>
<default>true</default>
</schema>
<schema>
<key>xdmcp/Enable</key>
<signature>b</signature>
<default>false</default>
</schema>
<schema>
<key>xdmcp/MaxPending</key>
<signature>i</signature>
<default>4</default>
</schema>
<schema>
<key>xdmcp/MaxSessions</key>
<signature>i</signature>
<default>16</default>
</schema>
<schema>
<key>xdmcp/MaxWait</key>
<signature>i</signature>
<default>30</default>
</schema>
<schema>
<key>xdmcp/DisplaysPerHost</key>
<signature>i</signature>
<default>1</default>
</schema>
<schema>
<key>xdmcp/Port</key>
<signature>i</signature>
<default>177</default>
</schema>
<schema>
<key>xdmcp/HonorIndirect</key>
<signature>b</signature>
<default>true</default>
</schema>
<schema>
<key>xdmcp/MaxWaitIndirect</key>
<signature>i</signature>
<default>30</default>
</schema>
<schema>
<key>xdmcp/PingIntervalSeconds</key>
<signature>i</signature>
<default>60</default>
</schema>
<schema>
<key>xdmcp/Willing</key>
<signature>s</signature>
<default>/etc/gdm/Xwilling</default>
</schema>
</schemalist>
</gdmschemafile>
如若实现普通用户的登陆，请自行将“leekwen”改为此用户名，重新reboot 机器即可。