Unable to write file: Read-only file system

I'm using the R2021a on MacOS Big Sur. I'm trying to run a script on that needs to write a file using the save command. I keep getting the following error:

Error using save

Unable to write file /Testing: Read-only file system.

The script runs the function:

save([dlocs{ii},filesep,dnames{ii}],'mov','-v7.3');

Where the first parameter are all preassigned variables and 'mov' is a temporary string variable. Testing is the filename of a .tif file.

The attributes of Testing.tif are:

archive: NaN

system: NaN

hidden: NaN

directory: 0

UserRead: 1

UserWrite: 1

UserExecute: 0

GroupRead: 1

GroupWrite: 0

GroupExecute: 0

OtherRead: 1

OtherWrite: 0

OtherExecute: 0

I have admin access to all files on the computer that I am using.

[Adam Decker]

The directory attributes are

archive: NaN

system: NaN

hidden: NaN

directory: 1

UserRead: 1

UserWrite: 1

UserExecute: 1

GroupRead: 1

GroupWrite: 1

GroupExecute: 1

OtherRead: 1

OtherWrite: 1

OtherExecute: 1

Answer 1

[Zinea]

Hi Adam Decker,

The error message "Unable to write file /Testing: Read-only file system" suggests that the script is trying to save the file to the root directory (/) of your macOS filesystem, which is typically protected and not writable by user-level processes. This could be due to an incorrect path specified in the variables dlocs{ii} and dnames{ii}.

Here are some ways to resolve the issue:

1. Check the Path Variables

The variables "dlocs{ii}" and "dnames{ii}" determine where the “save” function attempts to write the file. You need to ensure that dlocs{ii} points to a directory where you have write access. Here's how you can check and correct the path:

Print the Path: Add a line of code before the save command to print the full path to the console. This will help you verify the path being used.

fullPath = fullfile(dlocs{ii}, dnames{ii}); 
disp(['Attempting to save to: ', fullPath]); 

Validate the Path: If the printed path is not what you expect, or if it's pointing to the root directory /, you need to adjust dlocs{ii} to point to a valid, writable directory.

2. Correct Directory Permissions

Even if the path is correct, the directory might not have the necessary write permissions. Here's how to check and modify permissions:

Using Finder: Navigate to the directory in Finder, right-click on it, and select 'Get Info'. Scroll down to 'Sharing & Permissions' and ensure that your user has 'Read & Write' access. If not, click the lock icon to make changes, and then set the appropriate permissions.

Using Terminal: Open the Terminal and use the "chmod" command to grant write access to your user. For example, to grant write access to the current user for a folder named 'MyFolder', you would use in bash:

chmod u+w /path_to_MyFolder 

By following these detailed steps, you should be able to possibly diagnose and fix the issue with the save function in MATLAB. If the problem persists, double-check the values of "dlocs{ii}" and "dnames{ii}" at runtime, and ensure that your script has the necessary permissions to write to the desired location.