{"record":{"id":"962510dfdf9204c6","repo":"apache/hadoop","slug":"failed-to-obtain-current-username","errorCode":null,"errorMessage":"Failed to obtain current username","messagePattern":"Failed to obtain current username","errorType":"exception","errorClass":"SecurityException","httpStatus":null,"severity":"error","filePath":"hadoop-hdfs-project/hadoop-hdfs-client/src/main/java/org/apache/hadoop/hdfs/web/KerberosUgiAuthenticator.java","lineNumber":40,"sourceCode":"import org.apache.hadoop.security.UserGroupInformation;\nimport org.apache.hadoop.security.authentication.client.Authenticator;\nimport org.apache.hadoop.security.authentication.client.KerberosAuthenticator;\nimport org.apache.hadoop.security.authentication.client.PseudoAuthenticator;\n\n/**\n * Use UserGroupInformation as a fallback authenticator\n * if the server does not use Kerberos SPNEGO HTTP authentication.\n */\npublic class KerberosUgiAuthenticator extends KerberosAuthenticator {\n  @Override\n  protected Authenticator getFallBackAuthenticator() {\n    return new PseudoAuthenticator() {\n      @Override\n      protected String getUserName() {\n        try {\n          return UserGroupInformation.getLoginUser().getUserName();\n        } catch (IOException e) {\n          throw new SecurityException(\"Failed to obtain current username\", e);\n        }\n      }\n    };\n  }\n}\n","sourceCodeStart":22,"sourceCodeEnd":46,"githubUrl":"https://github.com/apache/hadoop/blob/2add9630210752f88ceb1bb74eb65e37bf41da8e/hadoop-hdfs-project/hadoop-hdfs-client/src/main/java/org/apache/hadoop/hdfs/web/KerberosUgiAuthenticator.java#L22-L46","documentation":"KerberosUgiAuthenticator tries Kerberos SPNEGO first and falls back to pseudo authentication when the server does not negotiate Kerberos. Its fallback asks UserGroupInformation.getLoginUser() for the user name; if that call throws IOException, it wraps the failure in a SecurityException with this message. The WebHDFS request therefore fails before it is sent.","triggerScenarios":"A WebHDFS server responds without SPNEGO negotiation, causing PseudoAuthenticator fallback, while UserGroupInformation cannot establish a login user. Concrete triggers include no Kerberos ticket, no HADOOP_USER_NAME override, an unreadable JAAS/keytab configuration, or an OS user lookup failure.","commonSituations":"Running a job on a host without kinit; a container without HADOOP_USER_NAME; a partially Kerberos-enabled cluster where the client is secure but the WebHDFS endpoint is not; incorrect KRB5_CONFIG, JAAS file permissions, or JDK Kerberos settings.","solutions":["If pseudo authentication is intended, set HADOOP_USER_NAME to the authorized HDFS user before JVM startup or otherwise ensure UserGroupInformation can obtain a login user.","If Kerberos is required, run kinit, verify UserGroupInformation.getLoginUser(), and configure the server for SPNEGO so the fallback is not used.","Check JAAS/keytab paths, file permissions, KDC reachability, krb5.conf, and clock skew when Kerberos login is the underlying failure.","Align the client and cluster security configuration so a Kerberos-enabled client does not connect to an endpoint that only supports pseudo auth."],"exampleFix":"# before\njava -cp app.jar com.example.WebHdfsJob\n\n# after: pseudo-auth fallback has a login user\nexport HADOOP_USER_NAME=alice\njava -cp app.jar com.example.WebHdfsJob\n\n# or, for a Kerberos deployment\nkinit alice@EXAMPLE.COM && java -cp app.jar com.example.WebHdfsJob","handlingStrategy":"try-catch","validationCode":"try {\n  UserGroupInformation login = UserGroupInformation.getLoginUser();\n  LOG.info(\"WebHDFS login user: {}\", login.getUserName());\n} catch (IOException e) {\n  throw new IllegalStateException(\"Cannot establish a Hadoop login user; run kinit or set HADOOP_USER_NAME\", e);\n}","typeGuard":null,"tryCatchPattern":"try {\n  return fs.open(path);\n} catch (SecurityException e) {\n  if (\"Failed to obtain current username\".equals(e.getMessage())) {\n    throw new SecurityException(\"WebHDFS pseudo-auth fallback could not obtain a Hadoop login user\", e);\n  }\n  throw e;\n} catch (IOException e) {\n  if (e.getCause() instanceof SecurityException) {\n    throw (SecurityException) e.getCause();\n  }\n  throw e;\n}","preventionTips":["Set HADOOP_USER_NAME explicitly in containers that use pseudo-authenticated WebHDFS.","Validate UserGroupInformation.getLoginUser() during application startup.","Keep Kerberos, JAAS, krb5.conf, and server SPNEGO configuration aligned in secure clusters."],"tags":["java","hadoop","webhdfs","kerberos","authentication","usergroupinformation"],"backgroundTag":"kerberos-authentication-failure","analyzedSha":"2add9630210752f88ceb1bb74eb65e37bf41da8e","analyzedAt":"2026-08-22T19:55:07.957Z","schemaVersion":2},"datasetVersion":"2026-08-22T20:17:22.307Z"}