Secure File from Delete & Edit in ubuntu:
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Lock a folder from delete and edits:
sudo chattr +i -R /path/to/folder

Remove lock so I can re-edit or delete a folder:
sudo chattr -i -R /path/to/folder

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Lock a file from delete and edits:
sudo chattr +i /path/to/file

Remove lock so I can re-edit or delete a file:
sudo chattr -i /path/to/file

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Source: https://www.unixmen.com/secure-file-from-removal-in-linux-and-unix/
Date: February 20th, 2021