Adjust delay between probes

You can slow down or speed up scans by specifying the amount of time that Nmap will wait between probes. Scans are often slowed down in order to avoid detection. You need to specify the number of seconds Nmap will wait between each probe it sends to a given host. The flag used is --scan-delay. Here is an example:

root@kali:~# nmap --scan-delay 10s -p21,22,80,135
Starting Nmap 7.01 ( ) at 2016-03-05 18:47 CET
Nmap scan report for
Host is up (0.13s latency).
21/tcp open ftp
22/tcp closed ssh
80/tcp open http
135/tcp open msrpc
Nmap done: 1 IP address (1 host up) scanned in 51.11 seconds

As you can see from the output above, we’ve scanned 4 ports on the target host, with the 10 seconds wait time between probes. Note that this has slowed down the scan considerably (the scanning process for only 4 ports took 51 seconds).

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