Bash脚本处理影院DCP驱动器时chmod权限异常问题求助

Hey there! Let's break down this chmod problem you're facing with your theater DCP script. First, let's recap the context to make sure I'm aligned:

• Your script handles formatting drives, setting 777 permissions, copying DCP files, applying 555 permissions, and unmounting/ejecting drives
• All core functions work as expected, but you're hitting a snag with the chmod step—even though files copy over with correct initial permissions, the chmod 555 operation isn't behaving as intended

Here are the most likely culprits and steps to debug them:

1. Target Filesystem Doesn't Support Unix Permissions #

Many theater-grade external drives use filesystems like FAT32 or exFAT (common for cross-device compatibility), which don't natively support Unix-style permission bits (read/write/execute flags). When you run chmod on these filesystems, the command might not throw an error, but it won't actually modify the permissions.

To confirm this:

• Run df -T to list mounted filesystems and check the type of your target drive
• Or use mount | grep /path/to/target-drive to see the mount details—look for filesystem type and any permission-related mount options

If it's a FAT/exFAT drive, you'll need to set default permissions via mount options instead of using chmod. For example, when mounting, you can add:

mount -t exfat /dev/sdX1 /mnt/dcp-drive -o umask=0002,fmask=0002

(This sets equivalent 555 permissions for files and directories by default.)

2. Missing Recursive Flag in Chmod Command #

If your DCP content includes nested directories and files, running chmod 555 /target-path only modifies the top-level directory's permissions—not all the files and subdirectories inside. You need the -R (recursive) flag to apply changes to everything:

chmod -R 555 /path/to/mounted-dcp-drive

Double-check your script to make sure you included this flag. If you didn't, the top directory might show 555, but the actual DCP files will retain their original permissions.

3. Insufficient User Permissions #

Even if files copied correctly, modifying permissions requires elevated privileges (especially on system-mounted drives). If you're running the script as a regular user, the chmod command might fail silently or throw an "Operation not permitted" error.

• Try running the script with sudo (e.g., sudo ./your-dcp-script.sh) to ensure you have root-level access
• Alternatively, add sudo directly before the chmod line in your script (just make sure the user running the script has sudo privileges without a password prompt if this is automated)

4. Check for Hidden Errors with Verbose Execution #

To see exactly what's happening when the chmod step runs, execute your script in debug mode:

bash -x ./your-dcp-script.sh

This will print every command the script runs, including the exact chmod command and any error messages it generates. Look for lines starting with + chmod ...—if there's an error, it will show up right after that line.

You can also redirect stderr to a log file in your script to capture errors:

chmod -R 555 /target-path 2>> /var/log/dcp-script-errors.log

5. File Has Immutable Attribute #

Rare, but possible: if a file has the immutable attribute set, even root can't modify its permissions until the attribute is removed. Check this with:

lsattr /path/to/dcp-file

If you see an i in the output, remove the attribute first:

chattr -i /path/to/dcp-file

Then run chmod again.

内容的提问来源于stack exchange，提问作者tduff