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Centos 6.5 系统用了半年多都没有出问题，突然有一天root登录不上去了（提示：could not open session ），其它系统用户也无法登录。经过多天的百度，，终于解决了。
在论坛上还问了一下，哈哈！
我的系统环境：
[root@master ~]# uname -a
Linux master 2.6.32-431.el6.x86_64 #1 SMP Fri Nov 22 03:15:09 UTC 2013 x86_64 x86_64 x86_64 GNU/Linux
看两个我本地的配置文件 （主要是修改就是在这两个配置文件上）
cat /etc/security/limits.conf
#* soft core 0
#* hard rss 10000
#@student hard nproc 20
#@faculty soft nproc 20
#@faculty hard nproc 50
#ftp hard nproc 0
#@student - maxlogins 4
oracle soft nproc 2047
oracle hard nproc 16384
oracle soft nofile 1024
oracle hard nofile 65536
oracle soft stack 10240
oracle hard stack 32768
* soft nofile 2900000
* hard nofile 2900000
* soft nproc 131072
* hard nproc 131072
cat /etc/pam.d/login
#%PAM-1.0
auth [user_unknown=ignore success=ok ignore=ignore default=bad] pam_securetty.so
auth include system-auth
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 optional pam_ck_connector.so
session required /lib/security/pam_limits.so
session required pam_limits.so解决的过程请看论坛：