How do I get the metadata of a directory using Hadoop through the command line?
I have tried utilizing hdfs dfsadmin -fetchImage which resulted in an error. There were a few documents that said this metadata can be read through the fsimage, but I cannot seem to find an example of how to read this data.
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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
When using the Cloudera VM how can you access information in the HDFS? I know there isn't a direct path to the HDFS but I also don't see how to dynamically access it.
After creating a Hive Table through the Hive CLI I attempted to load some data from a file located in the HDFS:
load data inpath '/test/student.txt' into table student;
But then I just get this error:
FAILED: SemanticException Line 1:17 Invalid path ''/test/student.txt'': No files matching path hdfs://quickstart.cloudera:8020/test/student.txt
I also tried to just load data not in the HDFS into a Hive Table like so:
load data inpath '/home/cloudera/Desktop/student.txt' into table student;
However that just produced this error:
FAILED: SemanticException Line 1:17 Invalid path ''/home/cloudera/Desktop/student.txt'': No files matching path hdfs://quickstart.cloudera:8020/home/cloudera/Desktop/student.txt
Once again I see it trying to access data with the root of hdfs://quickstart.cloudera:8020 and I'm not sure what that is, but it doesn't seem to be the root directory for the HDFS.
I'm not sure what I'm doing wrong but I made sure the file is located in the HDFS so I don't know why this error is coming up or how to fix it.
how can you access information in the HDFS
Well, you certainly don't need to use Hive to do it. hdfs dfs commands are how you interact with HDFS.
I'm not sure what that is, but it doesn't seem to be the root directory for the HDFS
It is the root of HDFS. quickstart.cloudera is the hostname of the VM. Port 8020 is the HDFS port.
Your exceptions are from the difference in using the LOCAL keyword.
What you're doing
LOAD DATA INPATH <hdfs location>
VS what you seem to be wanting
LOAD DATA LOCAL INPATH <local file location>
Or if the files are in HDFS, it's not clear how you have put files into it, but HDFS definitely doesn't have a /home folder or a Desktop, so the second error at least makes sense.
Anyways, hdfs dfs -put /test/students.text /test/ is one way to upload your file, assuming the hdfs:///test folder already exists. Otherwise, hdfs dfs -put /test/students.text /test renames your file to /test on HDFS
Note: You can create an EXTERNAL TABLE over an HDFS directory, you don't need to use the LOAD DATA command.
I wanted to know about how to get a directory on my cluster (i.e MapR) in HDFS compatible format. I want to use this for saving spark checkpoint files. Do I need to run hdfs dfs -ls
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).
I am trying to copy some files from the hadoop HDFS to local. I used the following command
hadoop fs -copyToLocal <hdfs path> <local path>
The size of the file is just 80M. I had run a job before where I had no issue in copying files of size 70MB to local. However, this time I am having Input/Output error
copyToLocal: Input/output error
can anyone tell me what could have gone wrong?
It might be a space constraint on your machine. I had the same issue because the file was too big for it to be moved to my local machine. Once I made space, I was able to perform the copyToLocal operation.