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The "UnixShellScriptProgrammingGuide" page has been changed by SomeOtherAccount: https://wiki.apache.org/hadoop/UnixShellScriptProgrammingGuide?action=diff&rev1=20&rev2=21 Comment: More dynamic subcommands updates ## page was renamed from ShellScriptProgrammingGuide = Introduction = - With [[https://issues.apache.org/jira/browse/HADOOP-9902|HADOOP-9902]], the shell script code base has been refactored, with common functions and utilities put into a shell library (hadoop-functions.sh). Here are some tips and tricks to get the most out of using this functionality: = The Skeleton = - All properly built shell scripts contain the following sections: 1. `hadoop_usage` function that contains an alphabetized list of subcommands and their description. This is used when the user directly asks for help, a command line syntax error, etc. - 2. `HADOOP_LIBEXEC_DIR` configured. This should be the location of where `hadoop-functions.sh`, `hadoop-config.sh`, etc, are located. + 1. `HADOOP_LIBEXEC_DIR` configured. This should be the location of where `hadoop-functions.sh`, `hadoop-config.sh`, etc, are located. - 3. `HADOOP_NEW_CONFIG=true`. This tells the rest of the system that the code being executed is aware that it is using the new shell API and it will call the routines it needs to call on its own. If this isn't set, then several default actions that were done in Hadoop 2.x and earlier are executed and several key parts of the functionality are lost. + 1. `HADOOP_NEW_CONFIG=true`. This tells the rest of the system that the code being executed is aware that it is using the new shell API and it will call the routines it needs to call on its own. If this isn't set, then several default actions that were done in Hadoop 2.x and earlier are executed and several key parts of the functionality are lost. - 4. `$HADOOP_LIBEXEC_DIR/abc-config.sh` is executed, where abc is the subproject. HDFS scripts should call `hdfs-config.sh`. MAPRED scripts should call `mapred-config.sh` YARN scripts should call `yarn-config.sh`. Everything else should call `hadoop-config.sh`. This does a lot of standard initialization, processes standard options, etc. This is also what provides override capabilities for subproject specific environment variables. For example, the system will normally ignore `yarn-env.sh`, but `yarn-config.sh` will activate those settings. + 1. `$HADOOP_LIBEXEC_DIR/abc-config.sh` is executed, where abc is the subproject. HDFS scripts should call `hdfs-config.sh`. MAPRED scripts should call `mapred-config.sh` YARN scripts should call `yarn-config.sh`. Everything else should call `hadoop-config.sh`. This does a lot of standard initialization, processes standard options, etc. This is also what provides override capabilities for subproject specific environment variables. For example, the system will normally ignore `yarn-env.sh`, but `yarn-config.sh` will activate those settings. - 5. At this point, this is where the majority of your code goes. Programs should process the rest of the arguments and doing whatever their script is supposed to do. + 1. At this point, this is where the majority of your code goes. Programs should process the rest of the arguments and doing whatever their script is supposed to do. - 6. Before executing a Java program (preferably via hadoop_java_exec) or giving user output, call `hadoop_finalize`. This finishes up the configuration details: adds the user class path, fixes up any missing Java properties, configures library paths, etc. + 1. Before executing a Java program (preferably via hadoop_java_exec) or giving user output, call `hadoop_finalize`. This finishes up the configuration details: adds the user class path, fixes up any missing Java properties, configures library paths, etc. - 7. Either an `exit` or an `exec`. This should return 0 for success and 1 or higher for failure. + 1. Either an `exit` or an `exec`. This should return 0 for success and 1 or higher for failure. - = Adding a Subcommand to an Existing Script = + = Adding a Subcommand to an Existing Script (NOT hadoop-tools-based) = - In order to add a new subcommand, there are two things that need to be done: 1. Add a line to that script's `hadoop_usage` function that lists the name of the subcommand and what it does. This should be alphabetized. - 2. Add an additional entry in the case conditional. Depending upon what is being added, several things may need to be done: + 1. Add an additional entry in the case conditional. Depending upon what is being added, several things may need to be done: + a. Set the `HADOOP_CLASSNAME` to the Java method. b. Add $HADOOP_CLIENT_OPTS to $HADOOP_OPTS (or, for YARN apps, $YARN_CLIENT_OPTS to $YARN_OPTS) if this is an interactive application or for some other reason should have the user client settings applied. + c. For methods that can also be daemons, set `HADOOP_SUBCMD_SUPPORTDAEMONIZATION=true`. This will allow for the `--daemon` option to work. See more below. + d. If it supports security, set `HADOOP_SUBCMD_SECURESERVICE=true` and `HADOOP_SUBCMD_SECUREUSER` equal to the user that should run the daemon. - a. Set the `CLASS` to the Java method. + 1. If a new subcommand needs one or more extra environment variables: + a. Add documentation and a '''commented''' out example that shows the default setting. b. Add the default(s) to that subprojects' hadoop_subproject_init or hadoop_basic_init for common, using the current shell vars as a guide. (Specifically, it should allow overriding!) - b. Add $HADOOP_CLIENT_OPTS to $HADOOP_OPTS (or, for YARN apps, $YARN_CLIENT_OPTS to $YARN_OPTS) if this is an interactive application or for some other reason should have the user client settings applied. + = Adding a Subcommand to an Existing Script (hadoop-tools-based) = + As of HADOOP-12930, subcommands that come from hadoop-tools utilizing the Dynamic Subcommands functionality. This allows for end-users to replace/override these utilities with their own versions as well as prevent the classpath from exploding with extra dependencies. - c. For methods that can also be daemons, set `supportdaemonization=true`. This will allow for the `--daemon` option to work. See more below. + 1. Create a src/main/shellprofile.d directory + 1. Inside there, create a hadoop-name.sh file that contains the bash functions necessary to create a Dynamic Subcommand. Note that versions that ship with hadoop need to verify that the function doesn't already exist. (See, for example, hadoop-archives/src/main/shellprofile.d) + 1. Modify the hadoop-tools assembly to copy this shellprofile.d in the correct place. + 1. To get hadoop_add_to_classpath_tools functionality to work for your command, add the following to your pom.xml. This uses the Maven dependency plug-in to create a file that the build system will use to create the file needed by that function. - d. If it supports security, set `secure_service=true` and `secure_user` equal to the user that should run the daemon. - - 3. If a new subcommand needs one or more extra environment variables: - - a. Add documentation and a '''commented''' out example that shows the default setting. - - b. Add the default(s) to that subprojects' hadoop_subproject_init or hadoop_basic_init for common, using the current shell vars as a guide. (Specifically, it should allow overriding!) + {{{ + <plugin> + <groupId>org.apache.maven.plugins</groupId> + <artifactId>maven-dependency-plugin</artifactId> + <executions> + <execution> + <id>deplist</id> + <phase>compile</phase> + <goals> + <goal>list</goal> + </goals> + <configuration> + <!-- referenced by a built-in command --> + <outputFile>${project.basedir}/target/hadoop-tools-deps/${project.artifactId}.tools-builtin.txt</outputFile> + </configuration> + </execution> + </executions> + </plugin> + }}} = Better Practices = - * Avoid adding more globals or project specific globals and/or entries in *-env.sh and/or a comment at the bottom here. In a lot of cases, there is pre-existing functionality that already does what you might need to do. Additionally, every configuration option makes it that much harder for end users. If you do need to add a new global variable for additional functionality, start it with HADOOP_ for common, HDFS_ for HDFS, YARN_ for YARN, and MAPRED_ for MapReduce. It should be documented in either *-env.sh (for user overridable parts) or hadoop-functions.sh (for internal-only globals). This helps prevents our variables from clobbering other people. * Remember that abc_xyz_OPTS can and should act as a catch-all for Java daemon options. Custom heap environment variables and other custom daemon variables add unnecessary complexity for both the user and us. They should be avoided. In almost every case, it is better to have a global and apply it to all daemons to have a universal default. Users can/will override that variables as necessary in their init scripts. This also helps cover the case when functionality starts in one chunk of Hadoop but ends up in multiple places. @@ -69, +85 @@ * A decent shell lint is available at http://www.shellcheck.net . Mac users can `brew install shellcheck` to install it locally. Like lint, however, be aware that it will sometimes flag things that are legitimate. These can be marked using a 'shellcheck disable' comment. (Usually, the flag for $HADOOP_OPTS being called without quotes is our biggest offense that shellcheck flags. Our usage without quotes is correct for the current code base. It is, however, a bad practice and shellcheck is correct for telling us about it.) = Standard Environment Variables = - In addition to all of the variables documented in `*-env.sh` and `hadoop-layout.sh`, there are a handful of special env vars: * `HADOOP_HEAP_MAX` - This is the Xmx parameter to be passed to Java. (e.g., `"-Xmx1g"`). This is present for backward compatibility, however it should be added to `HADOOP_OPTS` via `hadoop_add_param HADOOP_OPTS Xmx "${JAVA_HEAP_MAX}"` prior to calling `hadoop_finalize`. @@ -84, +99 @@ * `HADOOP_SLAVE_NAMES` - This is the list of hosts the user passed via `--hostnames`. - = About Daemonization = - In branch-2 and previous, "daemons" were handled via wrapping "standard" command lines. If we concentrate on the functionality (vs. the code rot...) this has some interesting (and inconsistent) results, especially around logging and pid files. If you run the `*-daemon` version, you got a pid file and `hadoop.root.logger` is set to be `INFO,(something)`. When a daemon is run in non-daemon mode (e.g., straight up: `hdfs namenode`), no pid file is generated and `hadoop.root.logger` is kept as `INFO,console`. With no pid file generated, it is possible to run, e.g. hdfs namenode, both in *-daemon.sh mode and in straight up mode again. It also means that one needs to pull apart the process list to safely determine the status of the daemon since pid files aren't always created. This made building custom init scripts fraught with danger. This inconsistency has been a point of frustration for many operations teams. Post-HADOOP-9902, there is a slight change in the above functionality and one of the key reasons why this is an incompatible change. Sub-commands that were intended to run as daemons (either fully, e.g., namenode or partially, e.g. balancer) have all of this handling consolidated, helping to eliminate code rot as well as providing a consistent user experience across projects. daemon=true, which is a per-script local, but is consistent across the hadoop sub-projects, tells the latter parts of the shell code that this sub-command needs to have some extra-handling enabled beyond the normal commands. In particular, `supportdaemonization=true` sub-commands will always get pid and out files. They will prevent two being run on the same machine by the same user simultaneously (see footnote 1, however). They get some extra options on the java command line. Etc, etc. @@ -100, +113 @@ 1-... unless `HADOOP_IDENT_STRING` is modified appropriately. This means that post-HADOOP-9902, it is now possible to run two secure datanodes on the same machine as the same user, since all of the logs, pids, and outs, take that into consideration! QA folks should be very happy. = A New Subproject or Subproject-like Structure = - The following files should be the basis of the new bits: * libexec/(project)-config.sh --------------------------------------------------------------------- To unsubscribe, e-mail: common-commits-unsubscr...@hadoop.apache.org For additional commands, e-mail: common-commits-h...@hadoop.apache.org
