To open a file in read-only mode in vim on Linux or Unix, you can use the -R option when starting vim.
For example, to open the example.txt file in read-only mode, you can use the following command:
vim -R example.txt
This will open the example.txt file in vim, and you will not be able to make any changes to the file.
You can also open a file in read-only mode within vim by using the :view command. For example:
vim example.txt :view
This will open the example.txt file in vim, and you will not be able to make any changes to the file.
To exit read-only mode in vim, you can use the :q command to quit vim, or the :nohlsearch command to turn off the highlight search feature.
For more information about read-only mode in vim, you can refer to the vim documentation or search online for tutorials and examples.