Java低版本（低于7）Linux环境下文件创建失败排查求助

Let’s walk through why your program might not be generating answer.txt when test.txt is created—no errors doesn’t mean nothing’s going wrong, so let’s dig into the most likely culprits:

• Double-Check Directory Permissions
  Linux permissions are the usual suspect here. First, confirm the user running your Java program has read and write access to /mnt/fs_services/pid/data/users/sup/. Run these commands to verify:

  # Check directory permissions
  ls -ld /mnt/fs_services/pid/data/users/sup/
  # See which user your Java process is running as
  ps aux | grep java
  

  Also, don’t forget about security modules like SELinux or AppArmor—they can block file creation without throwing obvious errors. You can check audit logs (via ausearch -m avc) to see if they’re interfering.

• Fix the Busy-Wait Loop’s Blind Spots
  Your do-while loop is a busy-wait, which can miss file creation due to file system metadata caching, especially on network mounts. Add a short sleep to the loop to reduce CPU usage and give the file system time to sync:

  do { 
      file = new File(filePath);
      try {
          Thread.sleep(500); // Wait 500ms between checks
      } catch (InterruptedException e) {
          e.printStackTrace();
      }
  } while(!file.exists());
  

  Also, add debug prints to confirm the loop is exiting when test.txt is created:

  System.out.println("Found test.txt! Proceeding to create answer.txt...");
  

  This will tell you if the program is even reaching the createNewFile() step.

• Make Sure You’re Seeing All Errors
  You said there’s no error output, but e1.printStackTrace() writes to stderr, which might be redirected or hidden depending on how you’re running the program. If you’re using nohup or running it in the background, check nohup.out or the system journal.
  To make errors harder to miss, replace the printStackTrace line with explicit stderr output:

  System.err.println("Failed to create answer.txt: " + e1.getMessage());
  

• Check for Network File System Quirks
  The path /mnt/fs_services/ looks like a mounted network file system (NFS, SMB, etc.). These often have metadata caching delays that can make File.exists() return false even after the file is created.
  Test your program on a local directory like /tmp first—if it works there, the issue is with the mounted file system. For NFS, you might need to adjust mount options (like noac to disable attribute caching) to get more immediate file status updates.

• Rule Out Race Conditions
  Could test.txt be created and then deleted before your program finishes the loop? Unlikely, but possible if another process is manipulating the file. Add a check right after the loop to confirm test.txt still exists before creating answer.txt:

  if (file.exists()) {
      // Create answer.txt here
  } else {
      System.err.println("test.txt disappeared after detection!");
  }
  

内容的提问来源于stack exchange，提问作者Ivan Sanchez