今天朋友Dataguard备库无法同步主库的问题，大概场景如下：

1.备库startup，日志同步语句执行都没问题，但是备库就是无法同步主库的内容

2.观察了下备库的归档同步情况，发现都是0表示未同步主库数据过来，然后看了下警告日志文件的内容，发现如下问题

<msg time="2016-01-20T00:57:57.734+08:00" org_id="oracle" comp_id="rdbms"
 client_id='' type='UNKNOWN' level='16'
 host_id='testdg' host_addr='127.0.0.1' module=''
 pid='26257'>
 Check that the primary and standby are using a password file
 

<msg time="2016-01-20T00:57:57.735+08:00" org_id="oracle" comp_id="rdbms"
 client_id='' type='UNKNOWN' level='16'
 host_id='testdg' host_addr='127.0.0.1' module=''
 pid='26257'>
 and remote_login_passwordfile is set to SHARED or EXCLUSIVE,
 

<msg time="2016-01-20T00:57:57.735+08:00" org_id="oracle" comp_id="rdbms"
 client_id='' type='UNKNOWN' level='16'
 host_id='testdg' host_addr='127.0.0.1' module=''
 pid='26257'>
 and that the SYS password is same in the password files.
 

<msg time="2016-01-20T00:57:57.735+08:00" org_id="oracle" comp_id="rdbms"
 client_id='' type='UNKNOWN' level='16'
 host_id='testdg' host_addr='127.0.0.1' module=''
 pid='26257'>
       returning error ORA-16191
 

<msg time="2016-01-20T00:57:57.735+08:00" org_id="oracle" comp_id="rdbms"
 client_id='' type='UNKNOWN' level='16'
 host_id='testdg' host_addr='127.0.0.1' module=''
 pid='26257'>
 ------------------------------------------------------------
 

<msg time="2016-01-20T00:57:57.735+08:00" org_id="oracle" comp_id="rdbms"
 client_id='' type='UNKNOWN' level='16'
 host_id='testdg' host_addr='127.0.0.1' module=''
 pid='26257'>
 FAL[client, ARC2]:Error 16191 connecting to orcl for fetching gap sequence
 

<msg time="2016-01-20T00:57:57.735+08:00" org_id="oracle" comp_id="rdbms"
 client_id='' type='UNKNOWN' level='16'
 host_id='testdg' host_addr='127.0.0.1' module=''
 pid='26257'>
 Errors in file /home/oracle/diag/rdbms/dg/dg/trace/dg_arc2_26257.trc:
ORA-16191: Primary log shipping client not logged on standby
 

<msg time="2016-01-20T00:57:57.735+08:00" org_id="oracle" comp_id="rdbms"
 client_id='' type='UNKNOWN' level='16'
 host_id='testdg' host_addr='127.0.0.1' module=''
 pid='26257'>
 Errors in file /home/oracle/diag/rdbms/dg/dg/trace/dg_arc2_26257.trc:
ORA-16191: Primary log shipping client not logged on standby
 

3.问题解决方式其实很简单，在主库重新生成口令文件传到备库中即可。问题的主要思路还是要根据警告日志的内容做对应的排查。