External hard drive not allowing permission

Solution 1:

Or you could try and change the permission using the following command as an administrator account or your account, if it's the only account you set up.

sudo chmod -R 755 /<folder name or path>

The -R will take care of all the sub-directories while the 755 permission will give the OWNER full access, USER read and execute and OTHERS read and execute.

Read = 4, Write = 2, Execute = 1

Read (4) + Execute (1) = 5

Read (4) + Write (2) + Execute (1) = 7

These are applied to groups and there are 3 groups in the order OWNER followed by USER followed by OTHERS and hence 755