Though it copies.. but it gives this error?
On Fri, Mar 1, 2013 at 3:21 PM, jamal sasha <jamalsha...@gmail.com> wrote: > When I try this.. I get an error > cat: Unable to write to output stream. > > Are these permissions issue > How do i resolve this? > THanks > > > On Wed, Feb 20, 2013 at 12:21 PM, Harsh J <ha...@cloudera.com> wrote: > >> No problem JM, I was confused as well. >> >> AFAIK, there's no shell utility that can let you specify an offset # >> of bytes to start off with (similar to skip in dd?), but that can be >> done from the FS API. >> >> On Thu, Feb 21, 2013 at 1:14 AM, Jean-Marc Spaggiari >> <jean-m...@spaggiari.org> wrote: >> > Hi Harsh, >> > >> > My bad. >> > >> > I read the example quickly and I don't know why I tought you used tail >> > and not head. >> > >> > head will work perfectly. But tail will not since it will need to read >> > the entier file. My comment was for tail, not for head, and therefore >> > not application to the example you gave. >> > >> > >> > hadoop fs -cat 100-byte-dfs-file | tail -c 5 > 5-byte-local-file >> > >> > Will have to download the entire file. >> > >> > Is there a way to "jump" into a certain position in a file and "cat" >> from there? >> > >> > JM >> > >> > 2013/2/20, Harsh J <ha...@cloudera.com>: >> >> Hi JM, >> >> >> >> I am not sure how "dangerous" it is, since we're using a pipe here, >> >> and as you yourself note, it will only last as long as the last bytes >> >> have been got and then terminate. >> >> >> >> The -cat process will terminate because the >> >> process we're piping to will terminate first after it reaches its goal >> >> of -c <N bytes>; so certainly the "-cat" program will not fetch the >> >> whole file down but it may fetch a few bytes extra over communication >> >> due to use of read buffers (the extra data won't be put into the target >> >> file, and get discarded). >> >> >> >> We can try it out and observe the "clienttrace" logged >> >> at the DN at the end of the -cat's read. Here's an example: >> >> >> >> I wrote a 1.6~ MB file into a file called "foo.jar", see "bytes" >> >> below, its ~1.58 MB: >> >> >> >> 2013-02-20 23:55:19,777 INFO >> >> org.apache.hadoop.hdfs.server.datanode.DataNode.clienttrace: src: >> >> /127.0.0.1:58785, dest: /127.0.0.1:50010, bytes: 1658314, op: >> >> HDFS_WRITE, cliID: DFSClient_NONMAPREDUCE_915204057_1, offset: 0, >> >> srvID: DS-1092147940-192.168.2.1-50010-1349279636946, blockid: >> >> BP-1461691939-192.168.2.1-1349279623549:blk_2568668834545125596_73870, >> >> duration: 192289000 >> >> >> >> I ran the command "hadoop fs -cat foo.jar | head -c 5 > foo.xml" to >> >> store first 5 bytes onto a local file: >> >> >> >> Asserting that post command we get 5 bytes: >> >> ➜ ~ wc -c foo.xml >> >> 5 foo.xml >> >> >> >> Asserting that DN didn't IO-read the whole file, see the read op below >> >> and its "bytes" parameter, its only about 193 KB, not the whole block >> >> of 1.58 MB we wrote earlier: >> >> >> >> 2013-02-21 00:01:32,437 INFO >> >> org.apache.hadoop.hdfs.server.datanode.DataNode.clienttrace: src: >> >> /127.0.0.1:50010, dest: /127.0.0.1:58802, bytes: 198144, op: >> >> HDFS_READ, cliID: DFSClient_NONMAPREDUCE_-1698829178_1, offset: 0, >> >> srvID: DS-1092147940-192.168.2.1-50010-1349279636946, blockid: >> >> BP-1461691939-192.168.2.1-1349279623549:blk_2568668834545125596_73870, >> >> duration: 19207000 >> >> >> >> I don't see how this is anymore dangerous than doing a >> >> -copyToLocal/-get, which retrieves the whole file anyway? >> >> >> >> On Wed, Feb 20, 2013 at 9:25 PM, Jean-Marc Spaggiari >> >> <jean-m...@spaggiari.org> wrote: >> >>> But be careful. >> >>> >> >>> hadoop fs -cat will retrieve the entire file and last only when it >> >>> will have retrieve the last bytes you are looking for. >> >>> >> >>> If your file is many GB big, it will take a lot of time for this >> >>> command to complete and will put some pressure on your network. >> >>> >> >>> JM >> >>> >> >>> 2013/2/19, jamal sasha <jamalsha...@gmail.com>: >> >>>> Awesome thanks :) >> >>>> >> >>>> >> >>>> On Tue, Feb 19, 2013 at 2:14 PM, Harsh J <ha...@cloudera.com> wrote: >> >>>> >> >>>>> You can instead use 'fs -cat' and the 'head' coreutil, as one >> example: >> >>>>> >> >>>>> hadoop fs -cat 100-byte-dfs-file | head -c 5 > 5-byte-local-file >> >>>>> >> >>>>> On Wed, Feb 20, 2013 at 3:38 AM, jamal sasha <jamalsha...@gmail.com >> > >> >>>>> wrote: >> >>>>> > Hi, >> >>>>> > I was wondering in the following command: >> >>>>> > >> >>>>> > bin/hadoop dfs -copyToLocal hdfspath localpath >> >>>>> > can we have specify to copy not full but like xMB's of file to >> local >> >>>>> drive? >> >>>>> > >> >>>>> > Is something like this possible >> >>>>> > Thanks >> >>>>> > Jamal >> >>>>> >> >>>>> >> >>>>> >> >>>>> -- >> >>>>> Harsh J >> >>>>> >> >>>> >> >> >> >> >> >> >> >> -- >> >> Harsh J >> >> >> >> >> >> -- >> Harsh J >> > >
