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https://issues.apache.org/jira/browse/HDFS-245?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12797311#action_12797311
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Eli Collins commented on HDFS-245:
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Here's the final link resolution behavior based on discussion in HADOOP-6427.
Basically we dropped (for now) links that resolve relative to the default file
system of the file context accessing the link. Updated description follows:
{noformat}
Given a symbolic link of form:
<---X--->
fs://host/A/B/link
<-----Y----->
X is the scheme and authority that identify the file system, and Y is the
path leading up to the symlink "link". If Y is a symlink itself then
let Y' be the target of Y and X' be the scheme and authority of Y'.
Then link targets of the following form resolve as follows:
1. Fully qualified URI
fs://hostX/A/B/file Resolved according to the target file system.
2. Partially qualified (scheme but no host) URI
fs:///A/B/file Resolved according to the target file sytem. Eg
resolving a link to hdfs:///A will result in an
exception because HDFS URIs must be fully qualified,
while a link to file:///A will not since Hadoop's
local file systems require partially qualified URIs.
3. Relative path
path Resolves to <Y'><path>. Eg if Y resolves to
hdfs://host/A and path is "../B/file" then
<Y'><path> is hdfs://host/B/file
4. Absolute path
path Resolves to <X'><path>. Eg if Y resolves
hdfs://host/A/B and path is "/file" then
<X'><path> is hdfs://host/file
{noformat}
> Create symbolic links in HDFS
> -----------------------------
>
> Key: HDFS-245
> URL: https://issues.apache.org/jira/browse/HDFS-245
> Project: Hadoop HDFS
> Issue Type: New Feature
> Reporter: dhruba borthakur
> Assignee: Eli Collins
> Attachments: 4044_20081030spi.java, designdocv1.txt, designdocv2.txt,
> designdocv3.txt, HADOOP-4044-strawman.patch, symlink-0.20.0.patch,
> symlink-25-hdfs.patch, symlink-26-hdfs.patch, symlink-26-hdfs.patch,
> symLink1.patch, symLink1.patch, symLink11.patch, symLink12.patch,
> symLink13.patch, symLink14.patch, symLink15.txt, symLink15.txt,
> symlink16-common.patch, symlink16-hdfs.patch, symlink16-mr.patch,
> symlink17-common.txt, symlink17-hdfs.txt, symlink18-common.txt,
> symlink19-common-delta.patch, symlink19-common.txt, symlink19-common.txt,
> symlink19-hdfs-delta.patch, symlink19-hdfs.txt, symlink20-common.patch,
> symlink20-hdfs.patch, symlink21-common.patch, symlink21-hdfs.patch,
> symlink22-common.patch, symlink22-hdfs.patch, symlink23-common.patch,
> symlink23-hdfs.patch, symlink24-hdfs.patch, symlink27-hdfs.patch,
> symlink28-hdfs.patch, symLink4.patch, symLink5.patch, symLink6.patch,
> symLink8.patch, symLink9.patch
>
>
> HDFS should support symbolic links. A symbolic link is a special type of file
> that contains a reference to another file or directory in the form of an
> absolute or relative path and that affects pathname resolution. Programs
> which read or write to files named by a symbolic link will behave as if
> operating directly on the target file. However, archiving utilities can
> handle symbolic links specially and manipulate them directly.
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