Hadoop Administration and Maintenance

“Admins are not only to stop people from doing stupid things, also to stop them from doing clever things!”

In the Hadoop world, a Systems Administrator is called a Hadoop Administrator. Hadoop Admin Roles and Responsibilities include setting up Hadoop clusters. Other duties involve backup, recovery and maintenance. Hadoop administration requires good knowledge of hardware systems and excellent understanding of Hadoop architecture.

It’s easy to get started with Hadoop administration because Linux system administration is a pretty well-known beast, and because systems administrators are used to administering all kinds of existing complex applications. However, there are many common missteps we’re seeing that make us believe there’s a need for some guidance in Hadoop administration. Most of these mistakes come from a lack of understanding about how Hadoop works. Here are just a few of the common issues we find.

With increased adoption of Hadoop in traditional enterprise IT solutions and increased number of Hadoop implementations in production environment, the need for Hadoop Operations and Administration experts to take care of the large Hadoop Clusters is becoming vital.

What does a Hadoop Admin do on day to day ?

  • Installation and Configuration
  • Cluster Maintenance
  • Resource Management
  • Security Management
  • Troubleshooting
  • Cluster Monitoring
  • Backup And Recovery Task
  • Aligning with the systems engineering team to propose and deploy new hardware and software environments required for Hadoop and to expand existing environments.
  • Diligently teaming with the infrastructure, network, database, application and business intelligence teams to guarantee high data quality and availability.

Some of the potential problems, which Hadoop administrators face in day to day operations are caused due to:
Human: Humans cause most common errors in health of systems or machines. Even a simple mistake can create a disaster and lead to down time. To avoid these errors it is important to have proper and proactive diagnostic process in place.
Miss-configuration is another problem that Hadoop administrators come across. Even now, after so much of development in Hadoop, it is considered a young technology. Let us look at the solution to this problem. You need to perform the following steps to get rid of mis-configuration.
• Start with basic parameters related with storage and operation.
• Gain thorough understanding of what needs to be achieved and where we are?
• Do lot of trail runs before moving on with changes in production environment.
Next problem is Hardware. One would rarely hear about a problem related to memory, mother boards and disk controllers but hard drive is mostly the cause of most of the problems. Almost every manufacturer do specify different measures of drive such as: Mean time to failure, Mean time between failures. Hardware does not fail straight away, but they degrade over time and lead to different failures. HDFS is best in detecting corrupt data blocks and automatically replicate to new copies without human intervention.

Remaining factors causing problems for hadoop administrators are:
Resource exhaustion: It is also a major factor that causes problem. As an administrator, one should measure and track task failures so as to help the user identify and correct the processes. Repetitive task failures can occupy task slots and can also take away resources from other jobs. Therefore, it should be seen as a drain on overall capacity.Next is the Host identification and Naming. Incorrectly configured host configuration file, will lead to a situation where client will never be able to communicate with data nodes.
The other problem is network partition: it is a situation where network is unable to communicate with other hosts on segment of network. This means that host X on switch 1 cannot send messages to host Y present on switch 2.


If you are working on Hadoop, you’ll realize there are several shell commands available to manage your hadoop cluster.

1. Hadoop Namenode Commands

Command Description
hadoop namenode -format Format HDFS filesystem from Namenode
hadoop namenode -upgrade Upgrade the NameNode
start-dfs.sh Start HDFS Daemons
stop-dfs.sh Stop HDFS Daemons
start-mapred.sh Start MapReduce Daemons
stop-mapred.sh Stop MapReduce Daemons
hadoop namenode -recover -force Recover namenode metadata after a cluster failure (may lose data)

2. Hadoop fsck Commands

Command Description
hadoop fsck / Filesystem check on HDFS
hadoop fsck / -files Display files during check
hadoop fsck / -files -blocks Display files and blocks during check
hadoop fsck / -files -blocks -locations Display files, blocks and its location during check
hadoop fsck / -files -blocks -locations -racks Display network topology for data-node locations
hadoop fsck -delete Delete corrupted files
hadoop fsck -move Move corrupted files to /lost+found directory

3. Hadoop Job Commands

Command Description
hadoop job -submit <job-file> Submit the job
hadoop job -status <job-id> Print job status completion percentage
hadoop job -list all List all jobs
hadoop job -list-active-trackers List all available TaskTrackers
hadoop job -set-priority <job-id> <priority> Set priority for a job. Valid priorities: VERY_HIGH, HIGH, NORMAL, LOW, VERY_LOW
hadoop job -kill-task <task-id> Kill a task
hadoop job -history Display job history including job details, failed and killed jobs

4. Hadoop dfsadmin Commands

Command Description
hadoop dfsadmin -report Report filesystem info and statistics
hadoop dfsadmin -metasave file.txt Save namenode’s primary data structures to file.txt
hadoop dfsadmin -setQuota 10 /quotatest Set Hadoop directory quota to only 10 files
hadoop dfsadmin -clrQuota /quotatest Clear Hadoop directory quota
hadoop dfsadmin -refreshNodes Read hosts and exclude files to update datanodes that are allowed to connect to namenode. Mostly used to commission or decommsion nodes
hadoop fs -count -q /mydir Check quota space on directory /mydir
hadoop dfsadmin -setSpaceQuota /mydir 100M Set quota to 100M on hdfs directory named /mydir
hadoop dfsadmin -clrSpaceQuota /mydir Clear quota on a HDFS directory
hadooop dfsadmin -saveNameSpace Backup Metadata (fsimage & edits). Put cluster in safe mode before this command.

5. Hadoop Safe Mode (Maintenance Mode) Commands

The following dfsadmin commands helps the cluster to enter or leave safe mode, which is also called as maintenance mode. In this mode, Namenode does not accept any changes to the name space, it does not replicate or delete blocks.

Command Description
hadoop dfsadmin -safemode enter Enter safe mode
hadoop dfsadmin -safemode leave Leave safe mode
hadoop dfsadmin -safemode get Get the status of mode
hadoop dfsadmin -safemode wait Wait until HDFS finishes data block replication

6. Hadoop Configuration Files

File Description
hadoop-env.sh Sets ENV variables for Hadoop
core-site.xml Parameters for entire Hadoop cluster
hdfs-site.xml Parameters for HDFS and its clients
mapred-site.xml Parameters for MapReduce and its clients
masters Host machines for secondary Namenode
slaves List of slave hosts

7. Hadoop mradmin Commands

Command Description
hadoop mradmin -safemode get Check Job tracker status
hadoop mradmin -refreshQueues Reload mapreduce configuration
hadoop mradmin -refreshNodes Reload active TaskTrackers
hadoop mradmin -refreshServiceAcl Force Jobtracker to reload service ACL
hadoop mradmin -refreshUserToGroupsMappings Force jobtracker to reload user group mappings

8. Hadoop Balancer Commands

Command Description
start-balancer.sh Balance the cluster
hadoop dfsadmin -setBalancerBandwidth <bandwidthinbytes> Adjust bandwidth used by the balancer
hadoop balancer -threshold 20 Limit balancing to only 20% resources in the cluster

9. Hadoop Filesystem Commands

Command Description
hadoop fs -mkdir mydir Create a directory (mydir) in HDFS
hadoop fs -ls List files and directories in HDFS
hadoop fs -cat myfile View a file content
hadoop fs -du Check disk space usage in HDFS
hadoop fs -expunge Empty trash on HDFS
hadoop fs -chgrp hadoop file1 Change group membership of a file
hadoop fs -chown huser file1 Change file ownership
hadoop fs -rm file1 Delete a file in HDFS
hadoop fs -touchz file2 Create an empty file
hadoop fs -stat file1 Check the status of a file
hadoop fs -test -e file1 Check if file exists on HDFS
hadoop fs -test -z file1 Check if file is empty on HDFS
hadoop fs -test -d file1 Check if file1 is a directory on HDFS

10. Additional Hadoop Filesystem Commands

Command Description
hadoop fs -copyFromLocal <source> <destination> Copy from local fileystem to HDFS
hadoop fs -copyFromLocal file1 data e.g: Copies file1 from local FS to data dir in HDFS
hadoop fs -copyToLocal <source> <destination> copy from hdfs to local filesystem
hadoop fs -copyToLocal data/file1 /var/tmp e.g: Copies file1 from HDFS data directory to /var/tmp on local FS
hadoop fs -put <source> <destination> Copy from remote location to HDFS
hadoop fs -get <source> <destination> Copy from HDFS to remote directory
hadoop distcp hdfs:// hdfs:// Copy data from one cluster to another using the cluster URL
hadoop fs -mv file:///data/datafile /user/hduser/data Move data file from the local directory to HDFS
hadoop fs -setrep -w 3 file1 Set the replication factor for file1 to 3
hadoop fs -getmerge mydir bigfile Merge files in mydir directory and download it as one big file

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