Quick Apache Hadoop Admin Command Reference Examples

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 Submit the job
hadoop job -status 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 Set priority for a job. Valid priorities: VERY_HIGH, HIGH, NORMAL, LOW, VERY_LOW
hadoop job -kill-task 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 haadmin Commands

Command Description
hdfs haadmin -getServiceState nn1 Determine whether the given NameNode is active or standby.
hdfs haadmin -checkHealth nn1 Check the health of the given NameNode.
hdfs haadmin -transitionToActive --forcemanual nn1 Force transition for a NN to Active
hdfs haadmin -failover nn2 nn1 Failover NameNode

9.Hadoop Balancer Commands

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

10. 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

11.Additional Hadoop Filesystem Commands

Command Description
hadoop fs -copyFromLocal 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 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 Copy from remote location to HDFS
hadoop fs -get 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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