[Hadoop Wiki] Update of "UnixShellScriptProgrammingGuide" by SomeOtherAccount
Dear Wiki user, You have subscribed to a wiki page or wiki category on "Hadoop Wiki" for change notification. The "UnixShellScriptProgrammingGuide" page has been changed by SomeOtherAccount: https://wiki.apache.org/hadoop/UnixShellScriptProgrammingGuide?action=diff=20=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
[Hadoop Wiki] Update of UnixShellScriptProgrammingGuide by SomeOtherAccount
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The UnixShellScriptProgrammingGuide page has been changed by SomeOtherAccount:
https://wiki.apache.org/hadoop/UnixShellScriptProgrammingGuide?action=diffrev1=18rev2=19
In addition to all of the variables documented in `*-env.sh` and
`hadoop-layout.sh`, there are a handful of special env vars:
- * `JAVA_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`.
+ * `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`.
* `HADOOP_DAEMON_MODE` - This will be set to `start` or `stop` based upon
what `hadoop-config.sh` has determined from the command line options.
[Hadoop Wiki] Update of UnixShellScriptProgrammingGuide by SomeOtherAccount
Dear Wiki user, You have subscribed to a wiki page or wiki category on Hadoop Wiki for change notification. The UnixShellScriptProgrammingGuide page has been changed by SomeOtherAccount: https://wiki.apache.org/hadoop/UnixShellScriptProgrammingGuide?action=diffrev1=17rev2=18 * 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 add unnecessary complexity for both the user and us. They should be avoided. + * 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. * Avoid mutli-level `if`'s where the comparisons are static strings. Use case statements instead, as they are easier to read.
[Hadoop Wiki] Update of UnixShellScriptProgrammingGuide by SomeOtherAccount
Dear Wiki user, You have subscribed to a wiki page or wiki category on Hadoop Wiki for change notification. The UnixShellScriptProgrammingGuide page has been changed by SomeOtherAccount: https://wiki.apache.org/hadoop/UnixShellScriptProgrammingGuide?action=diffrev1=16rev2=17 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 + + This contains the new, common configuration/startup bits. At a minimum, it should contain the bootstrap stanza for hadoop-config.sh and a function called hadoop_subproject_init that does the actual, extra work that needs to be done. Variables should be HADOOP_(project)_(whatever) and should be initialized based off of the standard HADOOP_* variables. + + * bin/(project) or sbin/(project) + + User-facing commands, those should be in bin. Administrator commands should be in sbin. See the skeleton example up above on how to build these types of scripts. + + * conf/*-env.sh + + Ideally, this should follow the pattern already established by the other *-env.sh files. Entries in it can also be in hadoop-env.sh to provide for a consistent and much easier operational experience. +
[Hadoop Wiki] Update of UnixShellScriptProgrammingGuide by SomeOtherAccount
Dear Wiki user, You have subscribed to a wiki page or wiki category on Hadoop Wiki for change notification. The UnixShellScriptProgrammingGuide page has been changed by SomeOtherAccount: https://wiki.apache.org/hadoop/UnixShellScriptProgrammingGuide?action=diffrev1=14rev2=15 Comment: Update docs post-HADOOP-11208 which renamed the daemon variable 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 `daemon=true`. This will allow for the `--daemon` option to work. + c. For methods that can also be daemons, set `supportdaemonization=true`. This will allow for the `--daemon` option to work. See more below. d. If it supports security, set `secure_service=true` and `secure_user` equal to the user that should run the daemon. @@ -82, +82 @@ * `HADOOP_SLAVE_NAMES` - This is the list of hosts the user passed via `--hostnames`. + + = Daemonization = + + n 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's 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. + + So where does --daemon come in? The value of that is stored in a global called HADOOP_DAEMON_MODE. If the user doesn't set it specifically, it defaults to 'default'. This was done to allow the code to mostly replicate the behavior of branch-2 and previous when the *-daemon.sh code was NOT used. In other words, --daemon default (or no value provided), let's commands like hdfs namenode still run in the foreground, just now with pid and out files. --daemon start does the disown (previously a nohup), change the logging output from HADOOP_ROOT_LOGGER to HADOOP_DAEMON_ROOT_LOGGER, add some extra command line options, etc, etc similar to the *-daemon.sh commands. + + What happens if daemon mode is set for all commands? The big thing is the pid and out file creation and the checks around it. A user would only ever be able to execute one 'hadoop fs' command at a time because of the pid file! Less than ideal. + + To summarize, supportdaemonization=true tells the code that --daemon actually means something to the sub-command. Otherwise, --daemon is ignored. + + 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. +
[Hadoop Wiki] Update of UnixShellScriptProgrammingGuide by SomeOtherAccount
Dear Wiki user, You have subscribed to a wiki page or wiki category on Hadoop Wiki for change notification. The UnixShellScriptProgrammingGuide page has been changed by SomeOtherAccount: https://wiki.apache.org/hadoop/UnixShellScriptProgrammingGuide?action=diffrev1=15rev2=16 Comment: Minor cleanup of previous big edit. * `HADOOP_SLAVE_NAMES` - This is the list of hosts the user passed via `--hostnames`. - = Daemonization = + = About Daemonization = - n 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. + 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's 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. + 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. - So where does --daemon come in? The value of that is stored in a global called HADOOP_DAEMON_MODE. If the user doesn't set it specifically, it defaults to 'default'. This was done to allow the code to mostly replicate the behavior of branch-2 and previous when the *-daemon.sh code was NOT used. In other words, --daemon default (or no value provided), let's commands like hdfs namenode still run in the foreground, just now with pid and out files. --daemon start does the disown (previously a nohup), change the logging output from HADOOP_ROOT_LOGGER to HADOOP_DAEMON_ROOT_LOGGER, add some extra command line options, etc, etc similar to the *-daemon.sh commands. + So where does `--daemon` come in? The value of that is stored in a global called `HADOOP_DAEMON_MODE`. If the user doesn't set it specifically, it defaults to 'default'. This was done to allow the code to mostly replicate the behavior of
