I am using Hortonworks distribution and Ambari for Hadoop administration. Sometimes, HDFS has to be restarted and sometimes Namenode hangs in the process giving the following output:

2016-04-21 06:12:47,391 – Retrying after 10 seconds. Reason: Execution of ‘hdfs dfsadmin -fs hdfs://t-namenode1:8020 -safemode get | grep ‘Safe mode is OFF” returned 1.
2016-04-21 06:12:59,595 – Retrying after 10 seconds. Reason: Execution of ‘hdfs dfsadmin -fs hdfs://t-namenode1:8020 -safemode get | grep ‘Safe mode is OFF” returned 1.
2016-04-21 06:13:11,737 – Retrying after 10 seconds. Reason: Execution of ‘hdfs dfsadmin -fs hdfs://t-namenode1:8020 -safemode get | grep ‘Safe mode is OFF” returned 1.
2016-04-21 06:13:23,918 – Retrying after 10 seconds. Reason: Execution of ‘hdfs dfsadmin -fs hdfs://t-namenode1:8020 -safemode get | grep ‘Safe mode is OFF” returned 1.
2016-04-21 06:13:36,101 – Retrying after 10 seconds. Reason: Execution of ‘hdfs dfsadmin -fs hdfs://t-namenode1:8020 -safemode get | grep ‘Safe mode is OFF” returned 1.

To get out of this loop I run the following command from the command line on the Namenode:

sudo -u hdfs hdfs dfsadmin -safemode leave

The output is the following:

Safe mode is OFF

If you have High Availability in the cluster, something like this shows up:

Safe mode is OFF in t-namenode1/10.x.x.171:8020
Safe mode is OFF in t-namenode2/10.x.x.164:8020

After the command is executed, the Namenode restart process in Ambari continues.