alibaba/arthas · error · IOException

${name}: Is a directory

Error message

${name}: Is a directory

What it means

The Arthas shell redirect handler (for '>' and '>>' output redirection) refuses to open a path that is an existing directory, mirroring standard POSIX shell behavior. It throws IOException before attempting FileWriter creation, which would produce a more cryptic error.

Source

Thrown at core/src/main/java/com/taobao/arthas/core/shell/command/internal/RedirectHandler.java:30

 * 重定向处理类
 *
 * @author gehui 2017年7月27日 上午11:38:40
 * @author hengyunabc 2019-02-06
 */
public class RedirectHandler extends PlainTextHandler implements CloseFunction {
    private PrintWriter out;

    private File file;

    public RedirectHandler() {

    }

    public RedirectHandler(String name, boolean append) throws IOException {
        File file = new File(name);

        if (file.isDirectory()) {
            throw new IOException(name + ": Is a directory");
        }

        if (!file.exists()) {
            File parentFile = file.getParentFile();
            if (parentFile != null) {
                parentFile.mkdirs();
            }
        }
        this.file = file;
        out = new PrintWriter(new BufferedWriter(new FileWriter(file, append)));
    }

    @Override
    public String apply(String data) {
        data = super.apply(data);
        if (out != null) {
            out.write(data);
            out.flush();

View on GitHub (pinned to 21cf2e9ba5)

Solutions

1. Specify a file path, not a directory path.
2. Append a filename to the directory (e.g., /tmp/output.txt instead of /tmp).
3. Remove trailing slashes from the redirect target.

Example fix

// before (in Arthas shell)
thread > /tmp
// after
thread > /tmp/thread-dump.txt

// Before constructing RedirectHandler, check the target is not a directory
File f = new File(name);
if (f.isDirectory()) {
    throw new IOException(name + ": Is a directory — specify a file path");
}

try {
    RedirectHandler handler = new RedirectHandler(name, append);
} catch (IOException e) {
    if (e.getMessage().endsWith(": Is a directory")) {
        // redirect target is a directory — ask user for a file path
    }
}

When it happens

Trigger: Using output redirection in an Arthas shell command (e.g., 'thread > /tmp' or 'dashboard >> /var/log') where the target path is an existing directory.

Common situations: User specifies a directory path instead of a file; trailing slash on the path; a directory name collides with the intended file name; the parent directory is given by mistake.

Related errors

• ${filePath}: Is a directory
• can not find arthas-core.jar under arthasHome: ${arthasHome}
• Failed to create directory within ${TEMP_DIR_ATTEMPTS} attem
• File '{}' exists but is a directory
• File '{}' cannot be written to

AI-assisted analysis of alibaba/arthas@21cf2e9ba5 (2026-08-14). Data as JSON: /api/errors/be3478e2bfb9d221. Report an issue: GitHub.