I was learning hadoop and till now I configured 3 Node cluster
127.0.0.1 localhost
10.0.1.1 hadoop-namenode
10.0.1.2 hadoop-datanode-2
10.0.1.3 hadoop-datanode-3
My hadoop Namenode directory looks like below
hadoop
bin
data-> ./namenode ./datanode
etc
logs
sbin
--
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As I learned that when we upload a large file in the cluster in divide the file into blocks, I want to upload a 1Gig file in my cluster and want to see how it is being stored in datanode.
Can anyone help me with the commands to upload file and see where these blocks are being stored.
First, you need to check if you have Hadoop tools in your path, if not - I recommend integrate them into it.
One of the possible ways of uploading a file to HDFS:hadoop fs -put /path/to/localfile /path/in/hdfs
I would suggest you read the documentation and get familiar with high-level commands first as it will save you time
Hadoop Documentation
Start with "dfs" command, as this one of the most often used commands
Related
Is there a way to batch upload files to Hadoop under a Hortonworks VM running CentOS? I see I can use the Ambari - Sandbox's HDFS Files tool, but that only allows uploading one-by-one. Apparently you could use Redgate's HDFS Explorer in the past, but it's no longer available. Hadoop is made to process big data, but it's absurd having to upload all files one-by-one...
Thank you!
Of course you can use the * wildcard in copyFromLocal, f.e.:
hdfs dfs -copyFromLocal input/* /tmp/input
I'm trying to execute a spark program in cluster mode in Amazon Ec2 using
spark-submit --master spark://<master-ip>:7077 --deploy-mode cluster --class com.mycompany.SimpleApp ./spark.jar
And the class has a line that tries to read a file:
JavaRDD<String> logData = sc.textFile("/user/input/CHANGES.txt").cache();
I'm unable to read this txt file in cluster mode even if I'm able to read in standalone mode. In cluster mode, it's looking to read from hdfs. So I put the file in hdfs at /root/persistent-hdfs using
hadoop fs -mkdir -p /wordcount/input
hadoop fs -put /app/hadoop/tmp/input.txt /wordcount/input/input.txt
And I can see the file using hadoop fs -ls /workcount/input. But Spark is still unable to read the file. Any idea what I'm doing wrong. Thanks.
You might want to check the following points:
Is the file really in the persistent HDFS?
It seems that you just copy the input file from /app/hadoop/tmp/input.txt to /wordcount/input/input.txt, all in the node disk. I believe you misunderstand the functionality of the hadoop commands.
Instead, you should try putting the file explicitly in the persistent HDFS (root/persistent-hdfs/), and then loading it using the hdfs://... prefix.
Is the persistent HDFS server up?
Please take a look here, it seems Spark only starts the ephemeral HDFS server by default. In order to switch to the persistent HDFS server, you must do the following:
1) Stop the ephemeral HDFS server: /root/ephemeral-hdfs/bin/stop-dfs.sh
2) Start the persistent HDFS server: /root/persistent-hdfs/bin/start-dfs.sh
Please try these things, I hope they can serve you well.
I was going through the HADOOP fs commands list. I am little perplexed not to find any "cd" command in hadoop fs.
Why is it so? It might sound silly question for the HADOOP users, but as I am beginner I can not understand why there is no list of cd command in HADOOP fs level?
Think about it like this:
Hadoop has a special file system called "hdfs" which runs on top of existing say linux file system. There is no concept of current or present working directory a.k.a. pwd
Let's say we have following structure in hdfs:
d1/
d2/
f1
d3/
f2
d4/
f3
You could do cd in your Linux file system from moving from one to the other but do you think changing directory in hadoop would makes sense? HDFS is like virtual file system and you dont directly interact with hdfs except via hadoop command or job tracker.
HDFS provides various features that enable accessing HDFS(Hadoop Filesystem) easy on local machines or edge nodes. You have an option to mount HDFS using any of the following methods. Once Hadoop file system is mounted on your machine, you may use cd command to browse through the file system (It's is like mounting remote network filesystem like NAS)
Fuse dfs (Available from Hadoop 0.20 onwards )
NFSv3 Gateway access to HDFS data (Available from Hadoop version
Hadoop 2.2.0)
For various reasons, I have one hadoop installation on machine A, a second hadoop installation on cluster B, and a third hadoop installation on cluster C.
When I set up machine A, the xml files were set so that I could use the HDFS shell to find the HDFS on machine A.
I can rewrite the xml files on machine A so that the HDFS shell invoked from machine A sees a different HDFS by default.
However, I would like to be able to access all filesystems conveniently, without resetting the xml files.
Example: while logged in at machine A, I would like to copy a file from cluster B to cluster C with syntax something like:
hdfs dfs -cp hdfs://nn1.exampleB.com/file1 hdfs://nn2.exampleC.com/file2
Currently it seems that syntax does not work (although the errors are varied; sometimes they are EOF; other times they are network timeouts).
Should the above syntax be valid without modifications to the XML configuration files?
You should be using distcp command:
$ hadoop distcp hdfs://nn1:8020/foo/bar hdfs://nn2:8020/bar/foo
See more here: http://hadoop.apache.org/docs/r0.19.0/distcp.html
Can any one help me understand the data storage concept of hadoop?
As I understand it, hadoop deals with fs image and data blocks, and fsimage and edit logs paths are stored hdfs-site.xml. But what about the data blocks? Can anyone help me in this? I am little bit confused where the /user and /tmp dir is actually present in the filesystem.
I used this link to set up a single node hadoop cluster: http://www.michael-noll.com/tutorials/running-hadoop-on-ubuntu-linux-single-node-cluster/
Files are split into blocks and stored in the Hadoop Distributed File System (HDFS). Consult the HDFS module of Yahoo's Hadoop Tutorial for a description of HDFS. The directories stored in HDFS can be viewed by typing the following command into a terminal: hadoop dfs -ls
The Namenode's FSImage keeps track of which Datanode has which files. In the hdfs-site.xml file, the configuration 'dfs.data.dir' defines where the datanode stores the underlying files on the filesystem. This can be a comma separated list of directories (think multiple disks).