Which command should you use to ensure that all configured filesystem mounts are active?

Using the command mount -a is effective for ensuring that all configured filesystem mounts are active. This command reads the /etc/fstab file, which contains a list of filesystems that are intended to be mounted automatically during system boot. When this command is executed, it attempts to mount all filesystems specified in that file, ensuring they are up and running based on their configurations.

This command is particularly useful in scenarios where new filesystems have been added or changes have been made to the /etc/fstab file and you want to apply those changes without needing to restart the entire system. It helps maintain system availability and can swiftly activate any adjustments made.

In contrast, the other commands serve different purposes. For example, partprobe is used to inform the operating system of changes to disk partitions but does not manage filesystem mounts directly. The command swapon -s displays information about active swap space; it has no relation to filesystem mounts. Lastly, while systemctl is a command for managing system services and the state of the systemd unit files, it does not directly relate to the activation of filesystem mounts. Therefore, mount -a is the appropriate choice for activating all configured filesystem mounts.