Identify the drive and mount point:
`lsblk -f`
`df -h`
Unmount the drive:
`sudo umount /dev/sdXN`
Create a mount point if needed:
`sudo mkdir -p /mnt/external`
Mount the drive:
`sudo mount /dev/sdXN /mnt/external`
Change ownership:
`sudo chown -R $USER:$USER /mnt/external`
Change permissions:
`sudo chmod -R 755 /mnt/external`
If the drive is NTFS or exFAT, remount with ownership options:
`sudo umount /dev/sdXN`
`sudo mount -o uid=$(id -u),gid=$(id -g),umask=022 /dev/sdXN /mnt/external`
To make permissions permanent, edit `/etc/fstab`:
`sudo blkid`
`sudo nano /etc/fstab`
Add an entry for NTFS:
`UUID=YOUR-UUID /mnt/external ntfs-3g uid=1000,gid=1000,umask=022 0 0`
Add an entry for exFAT:
`UUID=YOUR-UUID /mnt/external exfat uid=1000,gid=1000,umask=022 0 0`
Save the file and test:
`sudo mount -a`
Verify permissions:
`ls -ld /mnt/external`