The individual services in Hadoop are each run under the ownership of a corresponding Unix account. These accounts are known as service users. These service users belong to a special Unix group. In addition there is a special service user for running smoke tests on components during installation and on-demand using the Services View of the Ambari Web GUI. Any of these users and groups can be customized using the Misc tab during the Customize Services installation step.
![[Note]](../common/images/admon/note.png) | Note |
|---|---|
Use the "Skip Group Modifications" option to not modify the Linux groups in the cluster. Choosing this option is typically required if your environment manages groups using LDAP and not on the local Linux machines. |
If you choose to customize names, Ambari checks to see if these custom accounts already exist. If they do not exist, Ambari creates them. The default accounts are always created during installation whether or not custom accounts are specified. These default accounts are not used and can be removed post-install.
| Note |
|---|---|
All new service user accounts, and any existing user accounts used as service users, must have a UID >= 1000. |
Table 2.5. Service Users
| Service | Component | Default User Account |
|---|---|---|
| HDFS |
NameNode SecondaryNameNode DataNode | hdfs |
| YARN |
NodeManager ResourceManager | yarn |
| MapReduce2 |
HistoryServer | mapred |
| Tez | Tez clients | tez[a] |
| HBase |
MasterServer RegionServer | hbase |
| Hive |
Hive Metastore HiveServer2 | hive |
| HCat | HCatalog Server | hcat |
| WebHCat | WebHCat Server | hcat |
| Falcon | Falcon Server | falcon[b] |
| Storm |
Masters (Nimbus, DRPC Server, Storm REST API, Server, Storm UI Server) Slaves (Supervisors, Logviewers) | storm[c] |
| Oozie | Oozie Server | oozie |
| Ganglia |
Ganglia Server Ganglia Monitors | nobody |
| Ganglia | RRDTool (with Ganglia Server) | rrdcahed[d] |
| Ganglia | Apache HTTP Server | apache[e] |
| PostgreSQL | PostgreSQL (with Ambari Server) | postgres[f] |
| Nagios | Nagios Server | nagios[g] |
| ZooKeeper | ZooKeeper | zookeeper |
| Smoke Test[h] | All | ambari-qa |
[a] Tez is available with HDP 2.1 Stack. Not applicable in HDP 2.0 Stack or earlier. [b] Falcon is available with HDP 2.1 Stack. Not applicable in HDP 2.0 Stack or earlier. [c] Storm is available with HDP 2.1 Stack. Not applicable in HDP 2.0 Stack or earlier. [d] Created as part of installing RRDTool, which is used to store metrics data collected by Ganglia. [e] Created as part of installing Apache HTTP Server, which is used to serve the Ganglia web UI. [f] Created as part of installing the default PostgreSQL database with Ambari Server. If you are not using the Ambari PostgreSQL database, this user is not needed. [g] If you plan to use an existing user account named “nagios”, that “nagios” account must either be in a group named “nagios” or you must customize the Nagios Group. [h] The Smoke Test user performs smoke tests against cluster services as part of the install process. It also can perform these on-demand from the Ambari Web GUI. | ||
Table 2.6. Service Group
| Service | Components | Default Group Account |
|---|---|---|
| All | All | hadoop |
| Nagios | Nagios Server | nagios |
| Ganglia | Ganglia Server Ganglia Monitor | nobody |
