What does the command 'chmod u+x filename' do?

The command 'chmod u+x filename' modifies the file permissions for the specified file, referred to as 'filename.' Specifically, the 'u' stands for the user, which typically refers to the owner of the file. The '+x' part of the command indicates that execute permission is being added.

When executed, this command allows the user (owner) to execute the file as a program or script, which is essential for files that need to be run, such as shell scripts. This modification is crucial for users who are managing scripts or applications, as it defines the level of access they have, particularly enabling the ability to run the file.

The other choices do not accurately describe the action of the 'chmod u+x' command. The command does not remove permissions or alter permissions for the group or others, nor does it add read permission. Instead, it specifically focuses on enhancing the execution capabilities for the user.