HDFS Commands | Hadoop Tutorial pdf

HDFS Commands

FS Shell
The FileSystem (FS) shell is invoked by bin/hadoop fs <args>. All the FS shell commands take path URIs as arguments. The URI format is scheme://autority/path. For HDFS the scheme is hdfs, and for the local filesystem the scheme is file. The scheme and authority are optional. If not specified, the default scheme specified in the configuration is used. An HDFS file or directory such as /parent/child can be specified as hdfs://namenodehost/parent/child or simply as /parent/child (given that your configuration is set to point to hdfs://namenodehost). Most of the commands in FS shell behave like corresponding Unix commands. Differences are described with each of the commands. Error information is sent to stderr and the output is sent to stdout.
cat
Usage: hadoop fs -cat URI [URI …]
Copies source paths to stdout.
Example:
hadoop fs -cat hdfs://nn1.example.com/file1 hdfs://nn2.example.com/file2
hadoop fs -cat file:///file3 /user/hadoop/file4
Exit Code: Returns 0 on success and -1 on error.
chgrp
Usage: hadoop fs -chgrp [-R] GROUP URI [URI …]
Change group association of files. With -R, make the change recursively through the directory structure. The user must be the owner of files, or else a super-user. Additional information is in the Permissions User Guide.
chmod
Usage: hadoop fs -chmod [-R] <MODE[,MODE]... | OCTALMODE> URI [URI …]
Change the permissions of files. With -R, make the change recursively through the directory structure. The user must be the owner of the file, or else a super-user. Additional information is in the Permissions User Guide.
chown
Usage: hadoop fs -chown [-R] [OWNER][:[GROUP]] URI [URI ]
Change the owner of files. With -R, make the change recursively through the directory structure. The user must be a super-user. Additional information is in the Permissions User Guide.
copyFromLocal
Usage: hadoop fs -copyFromLocal <localsrc> URI
Similar to put command, except that the source is restricted to a local file reference.
copyToLocal
Usage: hadoop fs -copyToLocal [-ignorecrc] [-crc] URI <localdst>
Similar to get command, except that the destination is restricted to a local file reference.
cp
Usage: hadoop fs -cp URI [URI …] <dest>
Copy files from source to destination. This command allows multiple sources as well in which case the destination must be a directory.
Example:
hadoop fs -cp /user/hadoop/file1 /user/hadoop/file2
hadoop fs -cp /user/hadoop/file1 /user/hadoop/file2 /user/hadoop/dir
Exit Code:
Returns 0 on success and -1 on error.
du
Usage: hadoop fs -du URI [URI …]
Displays aggregate length of files contained in the directory or the length of a file in case its just a file.
Example: hadoop fs -du /user/hadoop/dir1 /user/hadoop/file1 hdfs://nn.example.com/user/hadoop/dir1
Exit Code: Returns 0 on success and -1 on error.
dus
Usage: hadoop fs -dus <args>
Displays a summary of file lengths.
expunge
Usage: hadoop fs -expunge
Empty the Trash. Refer to HDFS Design for more information on Trash feature.
get
Usage: hadoop fs -get [-ignorecrc] [-crc] <src> <localdst>
Copy files to the local file system. Files that fail the CRC check may be copied with the -ignorecrc option. Files and CRCs may be copied using the -crc option.
Example:
hadoop fs -get /user/hadoop/file localfile
hadoop fs -get hdfs://nn.example.com/user/hadoop/file localfile
Exit Code:
Returns 0 on success and -1 on error.
getmerge
Usage: hadoop fs -getmerge <src> <localdst> [addnl]
Takes a source directory and a destination file as input and concatenates files in src into the destination local file. Optionally addnl can be set to enable adding a newline character at the end of each file.
ls
Usage: hadoop fs -ls <args>
For a file returns stat on the file with the following format: filename <number of replicas> filesize modification_date modification_time permissions userid groupid
For a directory it returns list of its direct children as in unix. A directory is listed as: dirname <dir> modification_time modification_time permissions userid groupid
Example: hadoop fs -ls /user/hadoop/file1 /user/hadoop/file2 hdfs://nn.example.com/user/hadoop/dir1 /nonexistentfile
Exit Code: Returns 0 on success and -1 on error.
lsr
Usage: hadoop fs -lsr <args>
Recursive version of ls. Similar to Unix ls -R.
mkdir
Usage: hadoop fs -mkdir <paths>
Takes path uri's as argument and creates directories. The behavior is much like unix mkdir -p creating parent directories along the path.
Example:
hadoop fs -mkdir /user/hadoop/dir1 /user/hadoop/dir2
hadoop fs -mkdir hdfs://nn1.example.com/user/hadoop/dir hdfs://nn2.example.com/user/hadoop/dir
Exit Code:
Returns 0 on success and -1 on error.
movefromLocal
Usage: dfs -moveFromLocal <src> <dst>
Displays a "not implemented" message.
mv
Usage: hadoop fs -mv URI [URI …] <dest>
Moves files from source to destination. This command allows multiple sources as well in which case the destination needs to be a directory. Moving files across filesystems is not permitted.
Example:
hadoop fs -mv /user/hadoop/file1 /user/hadoop/file2
hadoop fs -mv hdfs://nn.example.com/file1 hdfs://nn.example.com/file2 hdfs://nn.example.com/file3 hdfs://nn.example.com/dir1
Exit Code:
Returns 0 on success and -1 on error.
put
Usage: hadoop fs -put <localsrc> ... <dst>
Copy single src, or multiple srcs from local file system to the destination filesystem. Also reads input from stdin and writes to destination filesystem.
hadoop fs -put localfile /user/hadoop/hadoopfile
hadoop fs -put localfile1 localfile2 /user/hadoop/hadoopdir
hadoop fs -put localfile hdfs://nn.example.com/hadoop/hadoopfile
hadoop fs -put - hdfs://nn.example.com/hadoop/hadoopfile
Reads the input from stdin.
Exit Code:
Returns 0 on success and -1 on error.
rm
Usage: hadoop fs -rm URI [URI …]
Delete files specified as args. Only deletes non empty directory and files. Refer to rmr for recursive deletes.
Example:
hadoop fs -rm hdfs://nn.example.com/file /user/hadoop/emptydir
Exit Code:
Returns 0 on success and -1 on error.
rmr
Usage: hadoop fs -rmr URI [URI …]
Recursive version of delete.
Example:
hadoop fs -rmr /user/hadoop/dir
hadoop fs -rmr hdfs://nn.example.com/user/hadoop/dir
Exit Code:
Returns 0 on success and -1 on error.
setrep
Usage: hadoop fs -setrep [-R] <path>
Changes the replication factor of a file. -R option is for recursively increasing the replication factor of files within a directory.
Example:
hadoop fs -setrep -w 3 -R /user/hadoop/dir1
Exit Code:
Returns 0 on success and -1 on error.
stat
Usage: hadoop fs -stat URI [URI …]
Returns the stat information on the path.
Example:
hadoop fs -stat path
Exit Code: Returns 0 on success and -1 on error.
tail
Usage: hadoop fs -tail [-f] URI
Displays last kilobyte of the file to stdout. -f option can be used as in Unix.
Example:
hadoop fs -tail pathname
Exit Code: Returns 0 on success and -1 on error.
test
Usage: hadoop fs -test -[ezd] URI
Options:
-e check to see if the file exists. Return 0 if true.
-z check to see if the file is zero length. Return 0 if true
-d check return 1 if the path is directory else return 0.
Example:
hadoop fs -test -e filename
text
Usage: hadoop fs -text <src>
Takes a source file and outputs the file in text format. The allowed formats are zip and TextRecordInputStream.
touchz
Usage: hadoop fs -touchz URI [URI …]
Create a file of zero length.
Example:
hadoop -touchz pathname
Exit Code: Returns 0 on success and -1 on error.

http://hadoop.apache.org/docs/r0.18.3/hdfs_shell.html