Debian系统修改外部磁盘plugdev组所有权的影响咨询

Hey there! Let's break down the risks and considerations of changing the group ownership of your external drive from plugdev to ftp_datas on Raspbian (which is essentially Debian under the hood).

First, let's recall what the plugdev group does in Debian-based systems: it's a default group designed to let regular users access removable storage devices without needing root privileges. When you mount an external drive, the system often assigns plugdev as the group owner so users in that group can read/write to the drive.

Now, onto the potential risks and how to mitigate them:

Key Risks to Be Aware Of #

• Lost user access: If your regular user account relies on being in the plugdev group to access the drive, switching the group to ftp_datas will lock you out unless you add your user to the ftp_datas group first. This is probably the most common pitfall.
• Reverting to plugdev on remount: If you only change the group ownership manually without updating your mount configuration, the next time you unmount and remount the drive (or reboot), the system will likely reset the group back to plugdev. This happens because default mount rules (either via udev or fstab) specify plugdev as the default group for removable media.
• Service access issues: If any system services (like file managers, backup tools, or media servers) were accessing the drive via the plugdev group, those services will lose access unless their running user is added to ftp_datas or you adjust their permissions.
• Setgid directory behavior: If any directories on the drive have the setgid bit enabled (where new files inherit the directory's group), changing the group to ftp_datas means all new files will now inherit this group instead of plugdev—this might be exactly what you want for FTP access, but it's good to confirm.

Safe Steps to Make the Change #

1. Add your user to the ftp_datas group
   Run this command to ensure you still have access after the change:

   sudo usermod -aG ftp_datas your_username
   

   Log out and back in for the group change to take effect.

2. Test with a small directory first
   Don't jump straight to recursive changes. Pick a test directory, change its group, and verify you can still read/write:

   chgrp ftp_datas /mnt/external/test_dir
   

   Create a file, edit it, and delete it to confirm permissions work.

3. Recursively change group ownership (if tests pass)
   Use the -R flag to apply the change to all files and directories on the drive:

   sudo chgrp -R ftp_datas /mnt/external
   

   Note: If the drive is large, this might take a few minutes—don't interrupt the process.

4. Update mount configuration to make the change permanent
   Edit your /etc/fstab file to specify ftp_datas as the group for future mounts. Find the line for your external drive, and add gid=ftp_datas to the options section. For example:
   Before:

   /dev/sda1 /mnt/external ext4 defaults 0 2
   

   After:

   /dev/sda1 /mnt/external ext4 defaults,gid=ftp_datas 0 2
   

   Save the file, then unmount and remount the drive to apply the change:

   sudo umount /mnt/external
   sudo mount /mnt/external
   

5. Backup first (critical!)
   While chgrp doesn't modify file content, it's always wise to back up important data on the drive before making bulk permission changes—just in case you target the wrong path or run into unexpected issues.

Final Takeaway #

Changing the group ownership won't "break" the drive's interaction with Debian at a low level (the file system itself remains intact). The main risks are related to permission access, which are easily mitigated by preparing your user groups and updating your mount settings. As long as you ensure all users/services that need access to the drive are in ftp_datas, you should be good to go.

内容的提问来源于stack exchange，提问作者hojkoff