su切换用户出错：
configuration error - unknown item 'QUOTAS_ENAB' (notify administrator)
configuration error - unknown item 'NOLOGIN_STR' (notify administrator)
configuration error - unknown item 'ENV_HZ' (notify administrator)
configuration error - unknown item 'CHFN_AUTH' (notify administrator)
configuration error - unknown item 'CLOSE_SESSIONS' (notify administrator)
google一下，发现了一个解决方法：
# cd /etc
# mv login.defs login.defs_OLD
# mv login.defs.dpkg-dist login.defs
