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 2.1. Service Users
| Service | Component | Default User Account |
|---|---|---|
| HDFS |
NameNode SecondaryNameNode DataNode | hdfs |
| MapReduce |
JobTracker HistoryServer TaskTracker | mapred |
| Hive |
Hive Metastore HiveServer2 | hive |
| HCat | HCatalog Server | hcat |
| WebHCat | WebHCat Server | hcat |
| Oozie | Oozie Server | oozie |
| HBase |
MasterServer RegionServer | hbase |
| ZooKeeper | ZooKeeper | zookeeper |
| Ganglia |
Ganglia Server Ganglia Collectors | nobody |
| Nagios | Nagios Server | nagios[a] |
| Smoke Test[b] | All | ambari-qa |
[a] If you plan to use an existing user account named "nagios", that "nagios" account must be in a group named "nagios". If you customize this account, that account will be created and put in a group "nagios". [b] 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. | ||
