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From: Ling Kun <lkun.erlv@gmail.com>
Date: Thu, 11 Apr 2013 18:33:02 +0800
Message-ID: 
 <CAGREd1Kj2z_0zq7f-kTgzqXM38EDY+vSrr99emmjVcF4PjEyiQ@mail.gmail.com>
Subject: What is the difference between URI, Home Directory, Working Directory
 in FileSystem.java or HDFS
To: user <user@hadoop.apache.org>
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Dear all,
   I am a little confusing about the URI, Home Directory and Working
Directory in the FileSystem.java or HDFS.

  I have listed my understanding about these concept, can someone please
figure out whether I am correct?  Thanks.

   The Home directory: This is usually a directory for a specific Hadoop
users. And for the path, it is a user specific path. In HDFS, it is like
 HDFS://NameNode:port/user/USERNAME.

   The URI: Is this the root of the distributed filesystem. for HDFS, it is
just the HDFS://NameNode:port/ , each file/directory in the distributed
filesystem is just a file or subdirectory in this path.

   The working directory: I am a little confused about this variable. At a
given time, there exists only one instance of the filesystem class, and the
working dir is a private state of the FS. And during the job running,
hadoop will switch among several dirs, and the working dir will be modified
once it is switched. Like in the shared system dir, home dir, or
input/output dir.


   Although I have looked through the related document, I am still a little
confused about the java.net.URI,  java.io.File and
org.apache.hadoop.fs.Path class. It seems URI could be
hdfs://XXX/XXX/FILENAME, while Path only can be the path without the
scheme, hostname and the port.  For the File class, it is just an object
for a specific file.


Thanks

yours,
Ling Kun

-- 
http://www.lingcc.com

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<div dir=3D"ltr">Dear all,<div>=A0 =A0I am a little confusing about the=A0U=
RI, Home Directory and Working Directory in the FileSystem.java or HDFS.</d=
iv><div><br></div><div>=A0 I have listed my understanding about these conce=
pt, can someone please figure out whether I am correct? =A0Thanks.</div>

<div><br></div><div>=A0 =A0The Home directory: This is usually a directory =
for a specific Hadoop users. And for the path, it is a user specific path. =
In HDFS, it is like =A0HDFS://NameNode:port/user/USERNAME.</div><div><br></=
div>

<div>=A0 =A0The URI: Is this the root of the distributed filesystem. for HD=
FS, it is just the HDFS://NameNode:port/ , each file/directory in the distr=
ibuted filesystem is just a file or subdirectory in this path.</div><div><b=
r>

</div><div>=A0 =A0The working directory: I am a little confused about this =
variable. At a given time, there exists only one instance of the filesystem=
 class, and the working dir is a private state of the FS. And during the jo=
b running, hadoop will switch among=A0several dirs, and the working dir wil=
l be modified once it is switched. Like in the shared system dir, home dir,=
 or input/output dir.</div>

<div><br></div><div><br></div><div><br></div><div>=A0 =A0Although I have lo=
oked through the related document, I am still a little confused about the j=
ava.net.URI, =A0java.io.File and org.apache.hadoop.fs.Path class. It seems =
URI could be hdfs://XXX/XXX/FILENAME, while Path only can be the path witho=
ut the scheme, hostname and the port. =A0For the File class, it is just an =
object for a specific file.</div>

<div><br></div><div><br></div><div><br></div><div>Thanks</div><div><br></di=
v><div>yours,</div><div>Ling Kun<br clear=3D"all"><div><br></div>-- <br><a =
href=3D"http://www.lingcc.com">http://www.lingcc.com</a>
</div></div>

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