When you plug external hard drive to your MacBook pro or air and you can open files and view them but you can’t make change to connected external drive folder files and you cant move or you can’t modify files then the permissions are set to read only and to make changes you need to change permissions of external hard drive and then you will be able to make changes.
Due to hard disk format like NTFS then you will see the hard drive with read only permissions and if it is a new hard drive then you need to format it with mac supported hard drive format and then start using it by formatting hard drive with Mac supported ExFAT Format.
You can remove read only permissions on mac by going to disk utility and select the external hard drive and change permissions of folders on external hard drive or you can use chmod 777 command.
Hard Drive ‘Read Only’ Permission on Mac
Follow below methods and fix hard drive read only permissions of external hard drive on mac.
Step 1: Connect external hard to macbook pro or air and you will see your external hard drive
Step 2: Right click on external hard drive and select Get info option.
Step 3: Under sharing and permission in Get Info you will see read only option here
Step 4: Now, to change permissions of external hard drive open disk utility on your mac
Step 5: Select Hard Drive from the left side menu panel. (Make sure you backup data connecting to windows or supported hard drive first and then erase the hard disk).
Step 6: Select the Hard Disk in disk utility and Click on Erase option on top and Click on Drop down button next to Format option and select Mac supported ExFAT.
Step 7: Click on Erase and wait for hard drive to format with supported macOS format ExFat and click on Done.
Step 8: Now, go ahead and start using your connected external hard drive.
Thats it, this is how you change permissions of mac by erasing content and formatting hard dive with mac Supported ExFat format.
Use Third Party Apps
You can use third party software’s as well and install it on mac and fix read only permissions on external hard drive as well and few software’s may also support without erasing content on hard drive as well.