Some Nmap Commands

Turn on OS and version detection scanning script (IPv4)

nmap -A
nmap -v -A
nmap -A -iL /tmp/scanlist.txt

Find out if a host/network is protected by a firewall

nmap -sA

Scan a host when protected by the firewall

nmap -PN

Scan a network and find out which servers and devices are up and running
This is known as host discovery or ping scan:

nmap -sP

Sample outputs:

Host is up (0.00035s latency).
MAC Address: BC:AE:C5:C3:16:93 (Unknown)
Host is up (0.0038s latency).
MAC Address: 74:44:01:40:57:FB (Unknown)
Host is up.
Host nas03 ( is up (0.0091s latency).
MAC Address: 00:11:32:11:15:FC (Synology Incorporated)
Nmap done: 256 IP addresses (4 hosts up) scanned in 2.80 second

Only show open (or possibly open) ports

nmap --open

Show all packets sent and received

nmap --packet-trace

Scan a host using TCP ACK (PA) and TCP Syn (PS) ping
If firewall is blocking standard ICMP pings, try the following host discovery methods:

nmap -PS
nmap -PS 80,21,443
nmap -PA
nmap -PA 80,21,200-512

How do I detect remote operating system?
You can identify a remote host apps and OS using the -O option:

nmap -O
nmap -O --osscan-guess
nmap -v -O --osscan-guess


How to Clear DNS Cache in MacOS Sierra

  1. Open the Terminal application, found in the Utilities folder within Applications
  2. Enter the following command syntax exactly (use copy and paste if in doubt about syntax accuracy):
    sudo killall -HUP mDNSResponder;say DNS cache has been flushed
  3. Hit the Return/Enter key and enter the admin password when requested (this is necessary because of sudo privileges)
  4. Wait a few moments for the DNS cache to be cleared

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