Cannnot build java project in Eclipse: Parent of resource is marked 'read-only'

if changing existing file permissions is not possible, you can also specify the build folder separately (assuming you are able to write your changes into the .project file).

Right-click the project and click properties -> Build path

In there, change the default output folder.

I had the same issue and solved it by granting write access to my workspace folder.

Some hints of how doing that in Linux can be found at: Change read/write access of a folder in Ubuntu Linux