What causes "Read file: %s error" in apache/dolphinscheduler?

Check the logged cause above the throw to see the concrete IOException reason

apache/dolphinscheduler · error · RuntimeException

Read file: %s error

Error message

Read file: %s error

What it means

LogUtils.readPartFileContentFromLocal reads a slice (skipLine..skipLine+limit) of a local log file using Files.lines. If the file exists but an IOException occurs while streaming its lines, the IOException is logged and rethrown as a RuntimeException 'Read file: <path> error'. It indicates an I/O-level failure (permissions, file deleted mid-read, I/O error), not a missing file.

Source

Thrown at dolphinscheduler-common/src/main/java/org/apache/dolphinscheduler/common/utils/LogUtils.java:73

        }
        return new byte[0];
    }

    public static byte[] getFileContentBytesFromRemote(String filePath) {
        RemoteLogUtils.getRemoteLog(filePath);
        return getFileContentBytesFromLocal(filePath);
    }

    public static List<String> readPartFileContentFromLocal(String filePath,
                                                            int skipLine,
                                                            int limit) {
        File file = new File(filePath);
        if (file.exists() && file.isFile()) {
            try (Stream<String> stream = Files.lines(Paths.get(filePath))) {
                return stream.skip(skipLine).limit(limit).collect(Collectors.toList());
            } catch (IOException e) {
                log.error("read file error", e);
                throw new RuntimeException(String.format("Read file: %s error", filePath), e);
            }
        } else {
            throw new RuntimeException("The file path: " + filePath + " not exists");
        }
    }

    public static List<String> readPartFileContentFromRemote(String filePath,
                                                             int skipLine,
                                                             int limit) {
        RemoteLogUtils.getRemoteLog(filePath);
        return readPartFileContentFromLocal(filePath, skipLine, limit);
    }

    public static String rollViewLogLines(List<String> lines) {
        StringBuilder builder = new StringBuilder();
        final int MaxResponseLogSize = 65535;
        int totalLogByteSize = 0;
        for (String line : lines) {

View on GitHub (pinned to 02eac45a1b)

Solutions

Check the logged cause above the throw to see the concrete IOException reason
Verify the process user has read permission on the file and its parent directories
Confirm the file still exists and the storage mount is healthy before reading
Increase file descriptor limits if 'Too many open files' appears in the cause
Retry the read, or treat the file as gone and return an empty list/partial content to the UI

Example fix

// before
List<String> lines = LogUtils.readPartFileContentFromLocal(path, skip, limit);
// after
try {
    List<String> lines = LogUtils.readPartFileContentFromLocal(path, skip, limit);
} catch (RuntimeException e) {
    log.warn("Log file unreadable: {}", path, e);
    return Collections.emptyList();
}

Defensive patterns

Strategy: try-catch

Validate before calling

if (!Files.isReadable(Paths.get(filePath))) { throw new IllegalStateException("Log file not readable: " + filePath); }

Try / catch

try {
  List<String> lines = LogUtils.readPartFileContentFromLocal(filePath, skip, limit);
} catch (RuntimeException e) {
  log.warn("Failed to read log slice from {}: {}", filePath, e.getCause());
  lines = Collections.emptyList();
}

Prevention

Run master/worker/service processes as users with read access to log directories
Do not delete/rotate a log file while UI queries may still read it — use retention windows
Monitor storage mounts and fd limits on worker hosts
Read the wrapped cause for the concrete IOException before retrying

When it happens

Trigger: Calling readPartFileContentFromLocal(filePath, skipLine, limit) when Files.lines throws IOException: unreadable permissions, file removed/truncated between the exists() check and the read, device I/O error, or too many open files.

Common situations: Log viewer in DolphinScheduler reading a task log that was rotated/cleaned up by log-retention jobs while still referenced; running the service as a user lacking read permission on worker log directories; NFS/NAS mounts that dropped.

Understand the failure class

Background: "failed to read file", EACCES, ENOENT and "could not read <path>" errors: when a program can't read a file from disk — this error's family across 49 libraries.

Related errors

AI-assisted analysis of apache/dolphinscheduler@02eac45a1b (2026-09-06). Data as JSON: /api/errors/f360844dbbafb0b7. Report an issue: GitHub.