{"record":{"id":"ef702959584baacb","repo":"apache/hadoop","slug":"eio-ef7029","errorCode":"EIO","errorMessage":"fuseConnectAsThreadUid: failed to open a libhdfs connection!  error %d.\n","messagePattern":"fuseConnectAsThreadUid: failed to open a libhdfs connection!  error (.+?)\\.\n","errorType":"console","errorClass":null,"httpStatus":null,"severity":"error","filePath":"hadoop-hdfs-project/hadoop-hdfs-native-client/src/main/native/fuse-dfs/fuse_impls_truncate.c","lineNumber":52,"sourceCode":"\n  TRACE1(\"truncate\", path)\n\n  assert(path);\n  assert('/' == *path);\n  assert(dfs);\n\n  if (size != 0) {\n    return 0;\n  }\n\n  int ret = dfs_unlink(path);\n  if (ret != 0) {\n    return ret;\n  }\n\n  ret = fuseConnectAsThreadUid(&conn);\n  if (ret) {\n    fprintf(stderr, \"fuseConnectAsThreadUid: failed to open a libhdfs \"\n            \"connection!  error %d.\\n\", ret);\n    ret = -EIO;\n    goto cleanup;\n  }\n  fs = hdfsConnGetFs(conn);\n\n  int flags = O_WRONLY | O_CREAT;\n\n  hdfsFile file;\n  if ((file = (hdfsFile)hdfsOpenFile(fs, path, flags,  0, 0, 0)) == NULL) {\n    ERROR(\"Could not connect open file %s\", path);\n    ret = -EIO;\n    goto cleanup;\n  }\n\n  if (hdfsCloseFile(fs, file) != 0) {\n    ERROR(\"Could not close file %s\", path);\n    ret = -EIO;","sourceCodeStart":34,"sourceCodeEnd":70,"githubUrl":"https://github.com/apache/hadoop/blob/2add9630210752f88ceb1bb74eb65e37bf41da8e/hadoop-hdfs-project/hadoop-hdfs-native-client/src/main/native/fuse-dfs/fuse_impls_truncate.c#L34-L70","documentation":"Emitted by the fuse-dfs truncate handler when fuseConnectAsThreadUid() cannot obtain a libhdfs connection during a truncate-to-zero (which is implemented as dfs_unlink followed by recreating an empty file via hdfsOpenFile with O_WRONLY|O_CREAT). Truncates to a non-zero size silently return success without effect (an HDFS limitation); this error fires on the recreate step's connection failure and returns EIO. Note the file may already have been unlinked by the time this error is returned.","triggerScenarios":"truncate -s 0, shell redirection > file, or editors that truncate, when getUsername(uid) fails, the uid's Kerberos ticket cache is missing/stale, or hdfsBuilderConnect fails (CLASSPATH/JVM, wrong namenode URI/port, NameNode unreachable).","commonSituations":"Log-rotation scripts using truncate/-s 0 or copytruncate-style reopening on a Kerberized mount whose ticket expired; fuse_dfs environment losing Hadoop jars after a restart; uid without a passwd entry.","solutions":["Check fuse-dfs stderr above this message - fuseNewConnect names the cause (kinit hint or connect error code).","Refresh Kerberos credentials for the calling uid (kinit) and retry.","Verify the file state after this error - dfs_unlink already ran, so the file may be gone even though truncate reported EIO.","Validate fuse_dfs.conf namenode URI/port and NameNode health with hdfs dfs -ls.","Restart fuse_dfs with a correct CLASSPATH/LIBHDFS_OPTS if the JVM failed to start."],"exampleFix":null,"handlingStrategy":"validation","validationCode":"# before truncate-style log rotation through the mount\nklist -s || kinit \"$USER\"@EXAMPLE.COM\nCLASSPATH=\"$(hdfs classpath --glob)\" hdfs dfs -ls \"${HDFS_URI:-hdfs://nn:8020/}\" || exit 1\n# note: only truncate -s 0 has any effect through fuse-dfs","typeGuard":null,"tryCatchPattern":"if (truncate(mount_file, 0) < 0 && errno == EIO) {\n    /* recreate step could not connect; the file may already be unlinked - verify */\n    check_file_exists_and_recreate();\n}","preventionTips":["Remember fuse-dfs truncate-to-zero = unlink + recreate: on EIO the file may already be gone.","Do not rely on truncate to non-zero sizes through the mount - it silently succeeds with no effect.","Run log rotation with valid Kerberos credentials; rotation windows are the classic ticket-expiry trap.","Keep an unlogged-copy or HDFS snapshot policy if truncation-based rotation is used."],"tags":["c","fuse-dfs","libhdfs","kerberos","connection","eio","truncate"],"backgroundTag":"hdfs-connection-failed","analyzedSha":"2add9630210752f88ceb1bb74eb65e37bf41da8e","analyzedAt":"2026-08-22T19:55:07.957Z","schemaVersion":2},"datasetVersion":"2026-08-22T20:17:22.307Z"}