Techniques are described for providing users with access to perform commands on network-accessible computing resources. In some situations, permissions are established for user(s) to execute command(s) on computing node(s) provided by an online service, such as by maintaining various permission information externally to those provided computing nodes for use in controlling users' ability to access, use, and/or modify the provided computing nodes. An interface component may use such external permissions information to determine if a particular user is authorized to execute one or more particular commands on one or more particular computing nodes, and to initiate simultaneous and independent execution of the command(s) on the computing node(s) when authorized. The interface component may further aggregate results from each computing node that executed the command(s), prior to providing the results to the user.