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Monday, 25 June 2018

Hadoop - Command Reference

There are many more commands in "$HADOOP_HOME/bin/hadoop fs"than are demonstrated here, although these basic operations will get you started. Running ./bin/hadoop dfs with no additional arguments will list all the commands that can be run with the FsShell system. Furthermore, $HADOOP_HOME/bin/hadoop fs -help commandName will display a short usage summary for the operation in question, if you are stuck.
A table of all the operations is shown below. The following conventions are used for parameters:
"<path>" means any file or directory name. 
"<path>..." means one or more file or directory names. 
"<file>" means any filename. 
"<src>" and "<dest>" are path names in a directed operation. 
"<localSrc>" and "<localDest>" are paths as above, but on the local file system. 
All other files and path names refer to the objects inside HDFS.
ls <path>
Lists the contents of the directory specified by path, showing the names, permissions, owner, size and modification date for each entry.
lsr <path>
Behaves like -ls, but recursively displays entries in all subdirectories of path.
du <path>
Shows disk usage, in bytes, for all the files which match path; filenames are reported with the full HDFS protocol prefix.
dus <path>
Like -du, but prints a summary of disk usage of all files/directories in the path.
mv <src><dest>
Moves the file or directory indicated by src to dest, within HDFS.
cp <src> <dest>
Copies the file or directory identified by src to dest, within HDFS.
rm <path>
Removes the file or empty directory identified by path.
rmr <path>
Removes the file or directory identified by path. Recursively deletes any child entries (i.e., files or subdirectories of path).
put <localSrc> <dest>
Copies the file or directory from the local file system identified by localSrc to dest within the DFS.
copyFromLocal <localSrc> <dest>
Identical to -put
moveFromLocal <localSrc> <dest>
Copies the file or directory from the local file system identified by localSrc to dest within HDFS, and then deletes the local copy on success.
get [-crc] <src> <localDest>
Copies the file or directory in HDFS identified by src to the local file system path identified by localDest.
getmerge <src> <localDest>
Retrieves all files that match the path src in HDFS, and copies them to a single, merged file in the local file system identified by localDest.
cat <filen-ame>
Displays the contents of filename on stdout.
copyToLocal <src> <localDest>
Identical to -get
moveToLocal <src> <localDest>
Works like -get, but deletes the HDFS copy on success.
mkdir <path>
Creates a directory named path in HDFS.
Creates any parent directories in path that are missing (e.g., mkdir -p in Linux).
setrep [-R] [-w] rep <path>
Sets the target replication factor for files identified by path to rep. (The actual replication factor will move toward the target over time)
touchz <path>
Creates a file at path containing the current time as a timestamp. Fails if a file already exists at path, unless the file is already size 0.
test -[ezd] <path>
Returns 1 if path exists; has zero length; or is a directory or 0 otherwise.
stat [format] <path>
Prints information about path. Format is a string which accepts file size in blocks (%b), filename (%n), block size (%o), replication (%r), and modification date (%y, %Y).
tail [-f] <file2name>
Shows the last 1KB of file on stdout.
chmod [-R] mode,mode,... <path>...
Changes the file permissions associated with one or more objects identified by path.... Performs changes recursively with R. mode is a 3-digit octal mode, or {augo}+/-{rwxX}. Assumes if no scope is specified and does not apply an umask.
chown [-R] [owner][:[group]] <path>...
Sets the owning user and/or group for files or directories identified by path.... Sets owner recursively if -R is specified.
chgrp [-R] group <path>...
Sets the owning group for files or directories identified by path.... Sets group recursively if -R is specified.
help <cmd-name>
Returns usage information for one of the commands listed above. You must omit the leading '-' character in cmd.

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