Nmap (Network Mapper) is a potent and multipurpose open-source utility mostly used by network administrators for network discovery and network security auditing. As a potent tool, it is sometimes necessary to halt or stop an Nmap scanning process while it’s in progress. To stop an ongoing Nmap scan, it involves using two common keyboard interrupts: ‘Ctrl + C’ or ‘Ctrl + ‘, which you can use depending on the situation.
The first method is using the ‘Ctrl + C’ keyboard shortcut which should immediately stop a running Nmap scan. ‘Ctrl + C’ sends the SIGINT (Interrupt From Keyboard) signal to Nmap program to stop its current task immediately. You can use this method when you realize there’s a mistake in the command or if the scan is taking too long (Kizza, Joseph Migga. “Guide to Computer Network Security.” London, Springer, 2013.)
The second method is the ‘Ctrl + ‘ keyboard sequence. If the ‘Ctrl + C’ fails to stop the Nmap scan, you can use ‘Ctrl + ‘ command, which sends the SIGQUIT signal to the Nmap program. It aborts the process in a way that allows it to terminate in an orderly manner and clean up its resources.
An important point to note is that if a particular Nmap scanning process was initiated with root or administrator privileges, the keyboard interrupt sequence used to stop it also needs to have the same elevated privileges to affect it in some systems.
While using Nmap, it is always recommended to follow best practices and act ethically to respect the privacy and ownership of others’ networks (Lyon, Gordon. “Nmap Network Scanning: The Official Nmap Project Guide to Network Discovery and Security Scanning.” Insecure, USA, 2009). Interrupting Nmap scans should be done carefully so as not to disrupt any existing network activities or leave any traces that may be considered malicious.
The technical information referred for this response has been derived from the comprehensive works and writings of Joseph Migga Kizza, in the book “Guide to Computer Network Security” and the Official Nmap project guide, “Nmap Network Scanning”, by Gordon Lyon. Both these sources are widely recognized and reliable in the field of computer networks and security.
