MyCATApache/Mycat-Server · error · IOException

Failed to create a temp directory

Error message

Failed to create a temp directory (under ${rootDir}) after ${maxAttempts} attempts!

What it means

createDirectory attempts up to MAX_DIR_CREATION_ATTEMPTS to create a uniquely-named temp subdirectory (UUID-suffixed) under a root directory. If every mkdirs() call fails or collides, it throws IOException. This guards against indefinite loops when the filesystem is broken or exhausted.

Solutions

1. Ensure the root directory exists and is writable by the process user (mkdir -p and chown/chmod it).
2. Check disk space and mount state (df -h; mount) for the filesystem holding rootDir.
3. Fix any configured scratch/spill directories pointing at read-only or nonexistent paths.
4. Catch IOException and fall back to an alternative temp root (e.g. java.io.tmpdir) with a logged warning.

Example fix

// before
File dir = JavaUtils.createDirectory(new File("/mnt/ro-scratch"), "blockmgr");
// after
File root = new File("/mnt/ro-scratch");
if (!root.canWrite()) root = new File(System.getProperty("java.io.tmpdir"));
File dir = JavaUtils.createDirectory(root, "blockmgr");

File root = new File(rootDir);
if (!root.isDirectory() || !root.canWrite()) { throw new IllegalStateException("scratch dir unusable: " + rootDir); }

try { return JavaUtils.createDirectory(root, prefix); } catch (IOException e) { log.warn("temp dir creation failed under {}", root, e); return JavaUtils.createDirectory(new File(System.getProperty("java.io.tmpdir")), prefix); }

When it happens

Trigger: Calling JavaUtils.createDirectory(rootDir) when rootDir does not exist or is not writable, the filesystem is full, or mkdirs() repeatedly fails (e.g. root is a read-only mount or a file exists with the same path prefix).

Common situations: Deployments where the configured local scratch directory (e.g. /tmp or a block-manager dir) is missing or read-only; disk-full conditions on data nodes; running as a user without write permission on the parent directory.

Understand the failure class

Background: "failed to write file", "Could not save figure", "Error saving remote file" — file write failed: causes and fixes across languages and libraries — this error's family across 38 libraries.

Related errors

• Mkdirs failed to create
• Failed to create local dir in $newDir.
• Failed to delete:
• Failed to list files for dir:
• Error opening jar

AI-assisted analysis of MyCATApache/Mycat-Server@65f8d8beb7 (2026-09-11). Data as JSON: /api/errors/7b8aa4da7a379c12. Report an issue: GitHub.

Appendix: source

Thrown at src/main/java/io/mycat/memory/unsafe/utils/JavaUtils.java:335

      unit = "KB";
    } else {
      value =   size;
      unit = "B";
    }

    return value + unit;
  }


  public static File createDirectory(String rootDir, String blockmgr) throws IOException {

    int attempts = 0;
    int maxAttempts = MAX_DIR_CREATION_ATTEMPTS;
    File dir = null;
    while (dir == null) {
      attempts += 1;
      if (attempts > maxAttempts) {
        throw new IOException("Failed to create a temp directory (under " + rootDir + ") after " +
                maxAttempts + " attempts!");
      }
      try {
        dir = new File(rootDir, blockmgr + "-" + UUID.randomUUID().toString());
        if (dir.exists() || !dir.mkdirs()) {
          dir = null;
        }
      } catch (Exception e) {
        logger.error(e.getMessage());
      }
    }

    return dir.getCanonicalFile();
  }

  /* Calculates 'x' modulo 'mod', takes to consideration sign of x,
* i.e. if 'x' is negative, than 'x' % 'mod' is negative too
* so function return (x % mod) + mod in that case.

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