Nmap not only adjusts itself to different network and target conditions while scanning, but it also supports several timing parameters, which can be tuned to improve performance.
The following recipe describes the timing parameters supported by Nmap.
Enter the following command to adjust the corresponding values:
# nmap -T4 --scan-delay 1s --initial-rtt-timeout 150ms --host-timeout 15m -d scanme.nmap.org
Nmap supports different timing arguments that can be tuned to improve performance. It is important to note that setting these values incorrectly will most likely hurt performance rather than improving it.
The RTT value is used by Nmap to know when to give up or retransmit a probe response. Nmap tries to determine the correct values by analyzing previous responses, but you can set the initial RTT timeout with the argument --initial-rtt-timeout, as shown in the following command:
# nmap -A -p- --initial-rtt-timeout 150ms <target>...