Which command can be used to terminate all running instances of smbd?

The command that can be used to terminate all running instances of smbd is "smbcontrol smbd shutdown." The "smbcontrol" command is specifically designed to send messages to Samba daemons, allowing you to manage and control them effectively. In this case, by specifying "smbd" as the target, you are instructing the command to send a shutdown signal to all running instances of the smbd service.

When smbd receives this shutdown command, it will begin to terminate gracefully, ensuring that any ongoing processes are completed before shutting down. This is particularly important for maintaining data integrity and ensuring that clients connected to the SMB shares are handled appropriately during the shutdown process.

The other options relate to different daemons or do not specify a target service effectively. For instance, nmbd is responsible for name resolution and browsing and doesn't control smbd. Similarly, the commands referencing "shutdown" without specifying the correct daemon won't achieve the desired outcome of terminating smbd instances directly. Thus, the command to use is indeed "smbcontrol smbd shutdown," as it precisely targets the correct service and function for graceful termination.