如果运行crontab如遇下面这样的错误：
$ crontab -l
You (zhangsan) are not allowed to access to (crontab) because of pam configuration.
原因可能是因为用户zhangsan密码过期了。当尝试以密码登录时，会报提示需要立即修改密码：
$ su - zhangsan
Password:
You are required to change your password immediately (password aged)
Changing password for zhangsan.
(current) UNIX password:
如果正好是hadoop集群，由于需要免密码登录，密码不能过期。
可以使用命名chage查看实际情况，比如（请以root用户运行）：
#chage -l zhangsan
Last password change : Nov 23, 2015
Password expires : Feb 21, 2016
Password inactive : never
Account expires : never
Minimum number of days between password change : 0
Maximum number of days between password change : 90
Number of days of warning before password expires : 7
从上可以看到：每90天需要修改一次密码，密码到期前7天会告警。
为了让密码永久有效，可这样设置一下：
chage -M 99999 zhangsan
再次查看：
#chage -l zhangsan
Last password change : Nov 23, 2015
Password expires : never
Password inactive : never
Account expires : never
Minimum number of days between password change : 0
Maximum number of days between password change : 99999
Number of days of warning before password expires : 7