挂载外置硬盘后新文件默认权限为777，如何修改为666？

Hey there! Let's tackle that permission problem you're facing with your external drive. The root cause lies in the mount options configured in /etc/fstab—the system file that handles automatic drive mounts. Here's a step-by-step solution to get those default file permissions down to a maximum of 666:

Step 1: Edit Your /etc/fstab File #

First, open the fstab file with root privileges to modify your drive's mount entry:

sudo nano /etc/fstab

Locate the line for your external drive—it starts with UUID= followed by your drive's unique ID, like this example (replace with your actual UUID and mount path):

UUID=1234-ABCD /mnt/external_drive vfat defaults 0 0

Step 2: Adjust Mount Options Based on Your Filesystem #

The exact options you'll add depend on whether your drive uses a Linux-native filesystem or a non-native one:

For Non-Native Filesystems (FAT32/NTFS) #

These filesystems don't store Linux-style permissions natively, so we use fmask (for files) and dmask (for directories) to set defaults directly:

• fmask=011: Calculates to 777 - 011 = 666 for files, giving you rw-rw-rw permissions (exactly the "max 666" you want).
• dmask=000: Sets directories to 777 (rwxrwxrwx), which is required to navigate and modify directory contents. If you prefer more restrictive directory permissions, use dmask=022 to get 755 (rwxr-xr-x).

Update your fstab line to look like this:

UUID=1234-ABCD /mnt/external_drive vfat defaults,fmask=011,dmask=000 0 0

For Linux-Native Filesystems (ext4, Btrfs, etc.) #

These filesystems respect standard Unix permissions. Use the umask option to set a reverse mask:

• umask=011: Results in files getting 666 (666 - 011 = 666) and directories getting 777 (777 - 011 = 777).

Your updated line will look like this:

UUID=abcd1234-efgh-ijkl-mnop-qrstuvwxyz1234 /mnt/external_drive ext4 defaults,umask=011 0 2

Step 3: Apply the Changes #

Save the fstab file (in nano, press Ctrl+O, hit Enter, then Ctrl+X). Then unmount and remount the drive to activate the changes immediately:

sudo umount /mnt/external_drive
sudo mount /mnt/external_drive

If you can't unmount the drive (e.g., it's in use), restart your system instead.

Verify the Fix #

Create a test file to confirm permissions are now correct:

touch /mnt/external_drive/test_file
ls -l /mnt/external_drive/test_file

You should see output showing permissions like -rw-rw-rw- (which corresponds to 666).

内容的提问来源于stack exchange，提问作者Luke W. Johnston