Which command is used to change the ownership of a file named doku.odt to a user named tux?

The command used to change the ownership of a file is 'chown'. In this scenario, the correct syntax is 'chown tux doku.odt', which specifically assigns ownership of the file 'doku.odt' to the user 'tux'. The command operates by taking two arguments: the new owner's name (in this case, 'tux') and the target file ('doku.odt').

Using 'chown' is essential for managing file permissions and ownership in a Linux system, as it allows administrators to control who can access or modify a file. This capability is fundamental in multi-user environments to ensure proper security and access control.

The other choices do not serve the purpose of changing file ownership. For instance, 'mv' is used to move or rename files, 'chgrp' changes the group ownership of a file, and 'chmod' modifies the permissions associated with a file. Each of these commands has its distinct function and does not directly affect file ownership in the manner specified in the question.