org.apache.hadoop.util
Class Shell

java.lang.Object
  org.apache.hadoop.util.Shell

Direct Known Subclasses:

DF, DU, Shell.ShellCommandExecutor, ShellCommand

public abstract class Shell
extends Object

A base class for running a Unix command. Shell can be used to run unix commands like du or df. It also offers facilities to gate commands by time-intervals.

Nested Class Summary

static class	Shell.ExitCodeException This is an IOException with exit code added.
static class	Shell.ShellCommandExecutor A simple shell command executor.

Field Summary

static org.apache.commons.logging.Log	LOG
static String	SET_GROUP_COMMAND
static String	SET_OWNER_COMMAND a Unix command to set owner
static String	SET_PERMISSION_COMMAND a Unix command to set permission
static String	USER_NAME_COMMAND a Unix command to get the current user's name
static boolean	WINDOWS Set to true on Windows platforms

Constructor Summary

Shell()

Shell(long interval)

Method Summary

static String	execCommand(String... cmd) Static method to execute a shell command.
protected abstract String[]	getExecString() return an array containing the command name & its parameters
int	getExitCode() get the exit code
static String[]	getGET_PERMISSION_COMMAND() Return a Unix command to get permission information.
static String[]	getGROUPS_COMMAND() a Unix command to get the current user's groups list
Process	getProcess() get the current sub-process executing the given command
static String[]	getUlimitMemoryCommand(JobConf job) Get the Unix command for setting the maximum virtual memory available to a given child process.
protected abstract void	parseExecResult(BufferedReader lines) Parse the execution result
protected void	run() check to see if a command needs to be executed and execute if needed
protected void	setEnvironment(Map<String,String> env) set the environment for the command
protected void	setWorkingDirectory(File dir) set the working directory

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

LOG

public static final org.apache.commons.logging.Log LOG

USER_NAME_COMMAND

public static final String USER_NAME_COMMAND

a Unix command to get the current user's name

See Also:

Constant Field Values

SET_PERMISSION_COMMAND

public static final String SET_PERMISSION_COMMAND

a Unix command to set permission

See Also:

Constant Field Values

SET_OWNER_COMMAND

public static final String SET_OWNER_COMMAND

a Unix command to set owner

See Also:

Constant Field Values

SET_GROUP_COMMAND

public static final String SET_GROUP_COMMAND

See Also:

Constant Field Values

WINDOWS

public static final boolean WINDOWS

Set to true on Windows platforms

Constructor Detail

Shell

public Shell()

Shell

public Shell(long interval)

Parameters:

interval - the minimum duration to wait before re-executing the command.

Method Detail

getGROUPS_COMMAND

public static String[] getGROUPS_COMMAND()

a Unix command to get the current user's groups list

getGET_PERMISSION_COMMAND

public static String[] getGET_PERMISSION_COMMAND()

Return a Unix command to get permission information.

getUlimitMemoryCommand

public static String[] getUlimitMemoryCommand(JobConf job)

Get the Unix command for setting the maximum virtual memory available to a given child process. This is only relevant when we are forking a process from within the Mapper or the Reducer implementations e.g. Hadoop Pipes or Hadoop Streaming. It also checks to ensure that we are running on a *nix platform else (e.g. in Cygwin/Windows) it returns null.

Parameters:

job - job configuration

Returns:

a String[] with the ulimit command arguments or null if we are running on a non *nix platform or if the limit is unspecified.

setEnvironment

protected void setEnvironment(Map<String,String> env)

set the environment for the command

Parameters:

env - Mapping of environment variables

setWorkingDirectory

protected void setWorkingDirectory(File dir)

set the working directory

Parameters:

dir - The directory where the command would be executed

run

protected void run()
            throws IOException

check to see if a command needs to be executed and execute if needed

Throws:

IOException

getExecString

protected abstract String[] getExecString()

return an array containing the command name & its parameters

parseExecResult

protected abstract void parseExecResult(BufferedReader lines)
                                 throws IOException

Parse the execution result

Throws:

IOException

getProcess

public Process getProcess()

get the current sub-process executing the given command

Returns:

process executing the command

getExitCode

public int getExitCode()

get the exit code

Returns:

the exit code of the process

execCommand

public static String execCommand(String... cmd)
                          throws IOException

Static method to execute a shell command. Covers most of the simple cases without requiring the user to implement the Shell interface.

Parameters:

cmd - shell command to execute.

Returns:

the output of the executed command.

Throws:

IOException