Top 32 Nmap Command Examples For Linux Admins

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last updated February 3, 2018 in Categories [Command Line Hacks][], [Howto][], [Networking][], [Security][]

Nmap is short for Network Mapper. It is an open source security tool for network exploration, security scanning and auditing. However, nmap command comes with lots of options that can make the utility more robust and difficult to follow for new users. The purpose of this post is to introduce a user to the nmap command line tool to scan a host and/or network, so to find out the possible vulnerable points in the hosts. You will also learn how to use Nmap for offensive and defensive purposes. Let us see some common nmap command examples.

[![nmap in action][]][nmap in action 1]

nmap in action

## What is Nmap and what is it used for? ##

From the man page:

> Nmap (“Network Mapper”) is an open source tool for network exploration and security auditing. It was designed to rapidly scan large networks, although it works fine against single hosts. Nmap uses raw IP packets in novel ways to determine what hosts are available on the network, what services (application name and version) those hosts are offering, what operating systems (and OS versions) they are running, what type of packet filters/firewalls are in use, and dozens of other characteristics. While Nmap is commonly used for security audits, many systems and network administrators find it useful for routine tasks such as network inventory, managing service upgrade schedules, and monitoring host or service uptime.

It was originally written by Gordon Lyon and it can answer the following questions easily:

1.  What computers did you find running on the local network?
2.  What IP addresses did you find running on the local network?
3.  What is the operating system of your target machine?
4.  Find out what ports are open on the machine that you just scanned?
5.  Find out if the system is infected with malware or virus.
6.  Search for unauthorized servers or network service on your network.
7.  Find and remove computers which don’t meet the organization’s minimum level of security.

## Sample setup (LAB) ##

Port scanning may be illegal in some jurisdictions. So setup a lab as follows:

+---------+
            +---------+           | Network |         +--------+
            | server1 |-----------+ swtich  +---------|server2 |
            +---------+           | (sw0)   |         +--------+
                                  +----+----+
                                       | 
                                       |
                             +---------+----------+
                             | wks01 Linux/OSX    |
                             +--------------------+

Where,

*  wks01 is your computer either running Linux/OS X or Unix like operating system. It is used for scanning your local network. The nmap command must be installed on this computer.
 *  server1 can be powered by Linux / Unix / MS-Windows operating systems. This is an unpatched server. Feel free to install a few services such as a web-server, file server and so on.
 *  server2 can be powered by Linux / Unix / MS-Windows operating systems. This is a [fully patched server with firewall][]. Again, feel free to install few services such as a web-server, file server and so on.
 *  All three systems are connected via switch.

## How do I install nmap? ##

See:

1.  [Debian / Ubuntu Linux: Install nmap Software For Scanning Network][Debian _ Ubuntu Linux_ Install nmap Software For Scanning Network]
2.  [CentOS / RHEL: Install nmap Network Security Scanner][CentOS _ RHEL_ Install nmap Network Security Scanner]
3.  [OpenBSD: Install nmap Network Security Scanner][OpenBSD_ Install nmap Network Security Scanner]

## \#1: Scan a single host or an IP address (IPv4) ##

<table> 
 <tbody> 
 <tr> 
 <td> <pre>### Scan a single ip address ###
nmap 192.168.1.1
&nbsp;
## Scan a host name ###
nmap server1.cyberciti.biz
&nbsp;
## Scan a host name with more info###
nmap -v server1.cyberciti.biz</pre> </td> 
 </tr> 
 </tbody> 
</table>

Sample outputs:

[![Fig.01: nmap output][Fig.01_ nmap output]][CentOS _ RHEL_ Install nmap Network Security Scanner]

Fig.01: nmap output

## \#2: Scan multiple IP address or subnet (IPv4) ##

nmap 192.168.1.1 192.168.1.2 192.168.1.3
    ## works with same subnet i.e. 192.168.1.0/24 
    nmap 192.168.1.1,2,3

You can scan a range of IP address too:

nmap 192.168.1.1-20

You can scan a range of IP address using a wildcard:

nmap 192.168.1.*

Finally, you scan an entire subnet:

nmap 192.168.1.0/24

## \#3: Read list of hosts/networks from a file (IPv4) ##

The -iL option allows you to read the list of target systems using a text file. This is useful to scan a large number of hosts/networks. Create a text file as follows:  
`cat > /tmp/test.txt`  
Sample outputs:

server1.cyberciti.biz
    192.168.1.0/24
    192.168.1.1/24
    10.1.2.3
    localhost

The syntax is:

nmap -iL /tmp/test.txt

## \#4: Excluding hosts/networks (IPv4) ##

When scanning a large number of hosts/networks you can exclude hosts from a scan:

nmap 192.168.1.0/24 --exclude 192.168.1.5
    nmap 192.168.1.0/24 --exclude 192.168.1.5,192.168.1.254

OR exclude list from a file called /tmp/exclude.txt

nmap -iL /tmp/scanlist.txt --excludefile /tmp/exclude.txt

## \#5: Turn on OS and version detection scanning script (IPv4) ##

nmap -A 192.168.1.254
    nmap -v -A 192.168.1.1
    nmap -A -iL /tmp/scanlist.txt

## \#6: Find out if a host/network is protected by a firewall ##

nmap -sA 192.168.1.254
    nmap -sA server1.cyberciti.biz

## \#7: Scan a host when protected by the firewall ##

nmap -PN 192.168.1.1
    nmap -PN server1.cyberciti.biz

## \#8: Scan an IPv6 host/address ##

The -6 option enable IPv6 scanning. The syntax is:

nmap -6 IPv6-Address-Here
    nmap -6 server1.cyberciti.biz
    nmap -6 2607:f0d0:1002:51::4
    nmap -v A -6 2607:f0d0:1002:51::4

## \#9: 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 192.168.1.0/24

Sample outputs:

Host 192.168.1.1 is up (0.00035s latency).
    MAC Address: BC:AE:C5:C3:16:93 (Unknown)
    Host 192.168.1.2 is up (0.0038s latency).
    MAC Address: 74:44:01:40:57:FB (Unknown)
    Host 192.168.1.5 is up.
    Host nas03 (192.168.1.12) 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

## \#10: How do I perform a fast scan? ##

nmap -F 192.168.1.1

## \#11: Display the reason a port is in a particular state ##

nmap --reason 192.168.1.1
    nmap --reason server1.cyberciti.biz

## \#12: Only show open (or possibly open) ports ##

nmap --open 192.168.1.1
    nmap --open server1.cyberciti.biz

## \#13: Show all packets sent and received ##

nmap --packet-trace 192.168.1.1
    nmap --packet-trace server1.cyberciti.biz

## 14\#: Show host interfaces and routes ##

This is useful for debugging ([ip command][] or [route command][] or [netstat command][] like output using nmap)

nmap --iflist

Sample outputs:

<table> 
 <tbody> 
 <tr> 
 <td> <pre>Starting Nmap 5.00 ( http://nmap.org ) at 2012-11-27 02:01 IST
************************INTERFACES************************
DEV (SHORT) IP/MASK TYPE UP MAC
lo (lo) 127.0.0.1/8 loopback up
eth0 (eth0) 192.168.1.5/24 ethernet up B8:AC:6F:65:31:E5
vmnet1 (vmnet1) 192.168.121.1/24 ethernet up 00:50:56:C0:00:01
vmnet8 (vmnet8) 192.168.179.1/24 ethernet up 00:50:56:C0:00:08
ppp0 (ppp0) 10.1.19.69/32 point2point up
&nbsp;
**************************ROUTES**************************
DST/MASK DEV GATEWAY
10.0.31.178/32 ppp0
209.133.67.35/32 eth0 192.168.1.2
192.168.1.0/0 eth0
192.168.121.0/0 vmnet1
192.168.179.0/0 vmnet8
169.254.0.0/0 eth0
10.0.0.0/0 ppp0
0.0.0.0/0 eth0 192.168.1.2</pre> </td> 
 </tr> 
 </tbody> 
</table>

## \#15: How do I scan specific ports? ##

<table> 
 <tbody> 
 <tr> 
 <td> <pre>nmap -p [port] hostName
## Scan port 80
nmap -p 80 192.168.1.1
&nbsp;
## Scan TCP port 80
nmap -p T:80 192.168.1.1
&nbsp;
## Scan UDP port 53
nmap -p U:53 192.168.1.1
&nbsp;
## Scan two ports ##
nmap -p 80,443 192.168.1.1
&nbsp;
## Scan port ranges ##
nmap -p 80-200 192.168.1.1
&nbsp;
## Combine all options ##
nmap -p U:53,111,137,T:21-25,80,139,8080 192.168.1.1
nmap -p U:53,111,137,T:21-25,80,139,8080 server1.cyberciti.biz
nmap -v -sU -sT -p U:53,111,137,T:21-25,80,139,8080 192.168.1.254
&nbsp;
## Scan all ports with * wildcard ##
nmap -p "*" 192.168.1.1
&nbsp;
## Scan top ports i.e. scan $number most common ports ##
nmap --top-ports 5 192.168.1.1
nmap --top-ports 10 192.168.1.1</pre> </td> 
 </tr> 
 </tbody> 
</table>

Sample outputs:

<table> 
 <tbody> 
 <tr> 
 <td> <pre>Starting Nmap 5.00 ( http://nmap.org ) at 2012-11-27 01:23 IST
Interesting ports on 192.168.1.1:
PORT STATE SERVICE
21/tcp closed ftp
22/tcp open ssh
23/tcp closed telnet
25/tcp closed smtp
80/tcp open http
110/tcp closed pop3
139/tcp closed netbios-ssn
443/tcp closed https
445/tcp closed microsoft-ds
3389/tcp closed ms-term-serv
MAC Address: BC:AE:C5:C3:16:93 (Unknown)
&nbsp;
Nmap done: 1 IP address (1 host up) scanned in 0.51 seconds</pre> </td> 
 </tr> 
 </tbody> 
</table>

## \#16: The fastest way to scan all your devices/computers for open ports ever ##

nmap -T5 192.168.1.0/24

## \#17: How do I detect remote operating system? ##

You can [identify a remote host apps and OS using the -O option][]:

<table> 
 <tbody> 
 <tr> 
 <td> <pre>nmap -O 192.168.1.1
nmap -O --osscan-guess 192.168.1.1
nmap -v -O --osscan-guess 192.168.1.1</pre> </td> 
 </tr> 
 </tbody> 
</table>

Sample outputs:

Starting Nmap 5.00 ( http://nmap.org ) at 2012-11-27 01:29 IST
    NSE: Loaded 0 scripts for scanning.
    Initiating ARP Ping Scan at 01:29
    Scanning 192.168.1.1 [1 port]
    Completed ARP Ping Scan at 01:29, 0.01s elapsed (1 total hosts)
    Initiating Parallel DNS resolution of 1 host. at 01:29
    Completed Parallel DNS resolution of 1 host. at 01:29, 0.22s elapsed
    Initiating SYN Stealth Scan at 01:29
    Scanning 192.168.1.1 [1000 ports]
    Discovered open port 80/tcp on 192.168.1.1
    Discovered open port 22/tcp on 192.168.1.1
    Completed SYN Stealth Scan at 01:29, 0.16s elapsed (1000 total ports)
    Initiating OS detection (try #1) against 192.168.1.1
    Retrying OS detection (try #2) against 192.168.1.1
    Retrying OS detection (try #3) against 192.168.1.1
    Retrying OS detection (try #4) against 192.168.1.1
    Retrying OS detection (try #5) against 192.168.1.1
    Host 192.168.1.1 is up (0.00049s latency).
    Interesting ports on 192.168.1.1:
    Not shown: 998 closed ports
    PORT   STATE SERVICE
    22/tcp open  ssh
    80/tcp open  http
    MAC Address: BC:AE:C5:C3:16:93 (Unknown)
    Device type: WAP|general purpose|router|printer|broadband router
    Running (JUST GUESSING) : Linksys Linux 2.4.X (95%), Linux 2.4.X|2.6.X (94%), MikroTik RouterOS 3.X (92%), Lexmark embedded (90%), Enterasys embedded (89%), D-Link Linux 2.4.X (89%), Netgear Linux 2.4.X (89%)
    Aggressive OS guesses: OpenWrt White Russian 0.9 (Linux 2.4.30) (95%), OpenWrt 0.9 - 7.09 (Linux 2.4.30 - 2.4.34) (94%), OpenWrt Kamikaze 7.09 (Linux 2.6.22) (94%), Linux 2.4.21 - 2.4.31 (likely embedded) (92%), Linux 2.6.15 - 2.6.23 (embedded) (92%), Linux 2.6.15 - 2.6.24 (92%), MikroTik RouterOS 3.0beta5 (92%), MikroTik RouterOS 3.17 (92%), Linux 2.6.24 (91%), Linux 2.6.22 (90%)
    No exact OS matches for host (If you know what OS is running on it, see http://nmap.org/submit/ ).
    TCP/IP fingerprint:
    OS:SCAN(V=5.00%D=11/27%OT=22%CT=1%CU=30609%PV=Y%DS=1%G=Y%M=BCAEC5%TM=50B3CA
    OS:4B%P=x86_64-unknown-linux-gnu)SEQ(SP=C8%GCD=1%ISR=CB%TI=Z%CI=Z%II=I%TS=7
    OS:)OPS(O1=M2300ST11NW2%O2=M2300ST11NW2%O3=M2300NNT11NW2%O4=M2300ST11NW2%O5
    OS:=M2300ST11NW2%O6=M2300ST11)WIN(W1=45E8%W2=45E8%W3=45E8%W4=45E8%W5=45E8%W
    OS:6=45E8)ECN(R=Y%DF=Y%T=40%W=4600%O=M2300NNSNW2%CC=N%Q=)T1(R=Y%DF=Y%T=40%S
    OS:=O%A=S+%F=AS%RD=0%Q=)T2(R=N)T3(R=N)T4(R=Y%DF=Y%T=40%W=0%S=A%A=Z%F=R%O=%R
    OS:D=0%Q=)T5(R=Y%DF=Y%T=40%W=0%S=Z%A=S+%F=AR%O=%RD=0%Q=)T6(R=Y%DF=Y%T=40%W=
    OS:0%S=A%A=Z%F=R%O=%RD=0%Q=)T7(R=N)U1(R=Y%DF=N%T=40%IPL=164%UN=0%RIPL=G%RID
    OS:=G%RIPCK=G%RUCK=G%RUD=G)IE(R=Y%DFI=N%T=40%CD=S)
    Uptime guess: 12.990 days (since Wed Nov 14 01:44:40 2012)
    Network Distance: 1 hop
    TCP Sequence Prediction: Difficulty=200 (Good luck!)
    IP ID Sequence Generation: All zeros
    Read data files from: /usr/share/nmap
    OS detection performed. Please report any incorrect results at http://nmap.org/submit/ .
    Nmap done: 1 IP address (1 host up) scanned in 12.38 seconds
               Raw packets sent: 1126 (53.832KB) | Rcvd: 1066 (46.100KB)

See also: [Fingerprinting a web-server][] and a [dns server][] command line tools for more information.

## \#18: How do I detect remote services (server / daemon) version numbers? ##

nmap -sV 192.168.1.1

Sample outputs:

Starting Nmap 5.00 ( http://nmap.org ) at 2012-11-27 01:34 IST
    Interesting ports on 192.168.1.1:
    Not shown: 998 closed ports
    PORT   STATE SERVICE VERSION
    22/tcp open  ssh     Dropbear sshd 0.52 (protocol 2.0)
    80/tcp open  http?
    1 service unrecognized despite returning data.

## \#19: 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 192.168.1.1
    nmap -PS 80,21,443 192.168.1.1
    nmap -PA 192.168.1.1
    nmap -PA 80,21,200-512 192.168.1.1

## \#20: Scan a host using IP protocol ping ##

nmap -PO 192.168.1.1

## \#21: Scan a host using UDP ping ##

This scan bypasses firewalls and filters that only screen TCP:

nmap -PU 192.168.1.1
    nmap -PU 2000.2001 192.168.1.1

## \#22: Find out the most commonly used TCP ports using TCP SYN Scan ##

<table> 
 <tbody> 
 <tr> 
 <td> <pre>### Stealthy scan ###
nmap -sS 192.168.1.1
&nbsp;
### Find out the most commonly used TCP ports using TCP connect scan (warning: no stealth scan)
### OS Fingerprinting ###
nmap -sT 192.168.1.1
&nbsp;
### Find out the most commonly used TCP ports using TCP ACK scan
nmap -sA 192.168.1.1
&nbsp;
### Find out the most commonly used TCP ports using TCP Window scan
nmap -sW 192.168.1.1
&nbsp;
### Find out the most commonly used TCP ports using TCP Maimon scan
nmap -sM 192.168.1.1</pre> </td> 
 </tr> 
 </tbody> 
</table>

## \#23: Scan a host for UDP services (UDP scan) ##

Most popular services on the Internet run over the TCP protocol. DNS, SNMP, and DHCP are three of the most common UDP services. Use the following syntax to find out UDP services:

nmap -sU nas03
    nmap -sU 192.168.1.1

Sample outputs:

<table> 
 <tbody> 
 <tr> 
 <td> <pre>Starting Nmap 5.00 ( http://nmap.org ) at 2012-11-27 00:52 IST
Stats: 0:05:29 elapsed; 0 hosts completed (1 up), 1 undergoing UDP Scan
UDP Scan Timing: About 32.49% done; ETC: 01:09 (0:11:26 remaining)
Interesting ports on nas03 (192.168.1.12):
Not shown: 995 closed ports
PORT STATE SERVICE
111/udp open|filtered rpcbind
123/udp open|filtered ntp
161/udp open|filtered snmp
2049/udp open|filtered nfs
5353/udp open|filtered zeroconf
MAC Address: 00:11:32:11:15:FC (Synology Incorporated)
&nbsp;
Nmap done: 1 IP address (1 host up) scanned in 1099.55 seconds</pre> </td> 
 </tr> 
 </tbody> 
</table>

## \#24: Scan for IP protocol ##

This type of scan allows you to determine which IP protocols (TCP, ICMP, IGMP, etc.) are supported by target machines:

nmap -sO 192.168.1.1

## \#25: Scan a firewall for security weakness ##

The following scan types exploit a subtle loophole in the TCP and good for testing security of common attacks:

<table> 
 <tbody> 
 <tr> 
 <td> <pre>## TCP Null Scan to fool a firewall to generate a response ##
## Does not set any bits (TCP flag header is 0) ##
nmap -sN 192.168.1.254
&nbsp;
## TCP Fin scan to check firewall ##
## Sets just the TCP FIN bit ##
nmap -sF 192.168.1.254
&nbsp;
## TCP Xmas scan to check firewall ##
## Sets the FIN, PSH, and URG flags, lighting the packet up like a Christmas tree ##
nmap -sX 192.168.1.254</pre> </td> 
 </tr> 
 </tbody> 
</table>

See [how to block Xmas packkets, syn-floods and other conman attacks][how to block Xmas packkets_ syn-floods and other conman attacks] with iptables.

## \#26: Scan a firewall for packets fragments ##

The -f option causes the requested scan (including ping scans) to use tiny fragmented IP packets. The idea is to split up the TCP header over  
several packets to make it harder for packet filters, intrusion detection systems, and other annoyances to detect what you are doing.

nmap -f 192.168.1.1
    nmap -f fw2.nixcraft.net.in
    nmap -f 15 fw2.nixcraft.net.in
    
    ## Set your own offset size with the --mtu option ##
    nmap --mtu 32 192.168.1.1

## \#27: Cloak a scan with decoys ##

The -D option it appear to the remote host that the host(s) you specify as [decoys are scanning the target network too][]. Thus their IDS might report 5-10 port scans from unique IP addresses, but they won’t know which IP was scanning them and which were innocent decoys:

nmap -n -Ddecoy-ip1,decoy-ip2,your-own-ip,decoy-ip3,decoy-ip4 remote-host-ip
    nmap -n -D192.168.1.5,10.5.1.2,172.1.2.4,3.4.2.1 192.168.1.5

## \#28: Scan a firewall for MAC address spoofing ##

<table> 
 <tbody> 
 <tr> 
 <td> <pre>### Spoof your MAC address ##
nmap --spoof-mac MAC-ADDRESS-HERE 192.168.1.1
&nbsp;
### Add other options ###
nmap -v -sT -PN --spoof-mac MAC-ADDRESS-HERE 192.168.1.1
&nbsp;
&nbsp;
### Use a random MAC address ###
### The number 0, means nmap chooses a completely random MAC address ###
nmap -v -sT -PN --spoof-mac 0 192.168.1.1</pre> </td> 
 </tr> 
 </tbody> 
</table>

## \#29: How do I save output to a text file? ##

The syntax is:

nmap 192.168.1.1 > output.txt
    nmap -oN /path/to/filename 192.168.1.1
    nmap -oN output.txt 192.168.1.1

## \#30 Scans for web servers and pipes into Nikto for scanning ##

`nmap -p80 192.168.1.2/24 -oG - | /path/to/nikto.pl -h - nmap -p80,443 192.168.1.2/24 -oG - | /path/to/nikto.pl -h -`

## \#31 Speed up nmap ##

Pass the -T option:  
`nmap -v -sS -A -T4 192.168.2.5`  
Sample outputs:

Starting Nmap 7.40 ( https://nmap.org ) at 2017-05-15 01:52 IST
    NSE: Loaded 143 scripts for scanning.
    NSE: Script Pre-scanning.
    Initiating NSE at 01:52
    Completed NSE at 01:52, 0.00s elapsed
    Initiating NSE at 01:52
    Completed NSE at 01:52, 0.00s elapsed
    Initiating ARP Ping Scan at 01:52
    Scanning 192.168.2.15 [1 port]
    Completed ARP Ping Scan at 01:52, 0.01s elapsed (1 total hosts)
    Initiating SYN Stealth Scan at 01:52
    Scanning dellm6700 (192.168.2.15) [1000 ports]
    Discovered open port 5900/tcp on 192.168.2.15
    Discovered open port 80/tcp on 192.168.2.15
    Discovered open port 22/tcp on 192.168.2.15
    Completed SYN Stealth Scan at 01:53, 4.62s elapsed (1000 total ports)
    Initiating Service scan at 01:53
    Scanning 3 services on dellm6700 (192.168.2.15)
    Completed Service scan at 01:53, 6.01s elapsed (3 services on 1 host)
    Initiating OS detection (try #1) against dellm6700 (192.168.2.15)
    Retrying OS detection (try #2) against dellm6700 (192.168.2.15)
    NSE: Script scanning 192.168.2.15.
    Initiating NSE at 01:53
    Completed NSE at 01:53, 30.02s elapsed
    Initiating NSE at 01:53
    Completed NSE at 01:53, 0.00s elapsed
    Nmap scan report for dellm6700 (192.168.2.15)
    Host is up (0.00044s latency).
    Not shown: 996 filtered ports
    PORT     STATE  SERVICE VERSION
    22/tcp   open   ssh     (protocol 2.0)
    | fingerprint-strings: 
    |   NULL: 
    |_    SSH-2.0-OpenSSH_7.4p1 Ubuntu-10
    | ssh-hostkey: 
    |   2048 1d:14:84:f0:c7:21:10:0e:30:d9:f9:59:6b:c3:95:97 (RSA)
    |_  256 dc:59:c6:6e:33:33:f2:d2:5d:9b:fd:b4:9c:52:c1:0a (ECDSA)
    80/tcp   open   http    nginx 1.10.0 (Ubuntu)
    | http-methods: 
    |_  Supported Methods: GET HEAD
    |_http-server-header: nginx/1.10.0 (Ubuntu)
    |_http-title: Apache2 Ubuntu Default Page: It works
    443/tcp  closed https
    5900/tcp open   vnc     VNC (protocol 3.7)
    1 service unrecognized despite returning data. If you know the service/version, please submit the following fingerprint at https://nmap.org/cgi-bin/submit.cgi?new-service :
    SF-Port22-TCP:V=7.40%I=7%D=5/15%Time=5918BCAA%P=x86_64-apple-darwin16.3.0%
    SF:r(NULL,20,"SSH-2\.0-OpenSSH_7\.4p1\x20Ubuntu-10\n");
    MAC Address: F0:1F:AF:1F:2C:60 (Dell)
    Device type: general purpose
    Running (JUST GUESSING): Linux 3.X|4.X|2.6.X (95%), OpenBSD 4.X (85%)
    OS CPE: cpe:/o:linux:linux_kernel:3 cpe:/o:linux:linux_kernel:4 cpe:/o:linux:linux_kernel:2.6.32 cpe:/o:openbsd:openbsd:4.0
    Aggressive OS guesses: Linux 3.11 - 4.1 (95%), Linux 4.4 (95%), Linux 3.13 (92%), Linux 4.0 (90%), Linux 2.6.32 (89%), Linux 2.6.32 or 3.10 (89%), Linux 3.2 - 3.8 (89%), Linux 3.10 - 3.12 (88%), Linux 2.6.32 - 2.6.33 (87%), Linux 2.6.32 - 2.6.35 (87%)
    No exact OS matches for host (test conditions non-ideal).
    Uptime guess: 0.000 days (since Mon May 15 01:53:08 2017)
    Network Distance: 1 hop
    TCP Sequence Prediction: Difficulty=252 (Good luck!)
    IP ID Sequence Generation: All zeros
    Service Info: OS: Linux; CPE: cpe:/o:linux:linux_kernel
    
    TRACEROUTE
    HOP RTT     ADDRESS
    1   0.44 ms dellm6700 (192.168.2.15)
    
    NSE: Script Post-scanning.
    Initiating NSE at 01:53
    Completed NSE at 01:53, 0.00s elapsed
    Initiating NSE at 01:53
    Completed NSE at 01:53, 0.00s elapsed
    Read data files from: /usr/local/bin/../share/nmap
    OS and Service detection performed. Please report any incorrect results at https://nmap.org/submit/ .
    Nmap done: 1 IP address (1 host up) scanned in 46.02 seconds
               Raw packets sent: 2075 (95.016KB) | Rcvd: 50 (3.084KB)

## \#32: Not a fan of command line tools? ##

Try [zenmap the official network mapper][] front end:

> Zenmap is the official Nmap Security Scanner GUI. It is a multi-platform (Linux, Windows, Mac OS X, BSD, etc.) free and open source application which aims to make Nmap easy for beginners to use while providing advanced features for experienced Nmap users. Frequently used scans can be saved as profiles to make them easy to run repeatedly. A command creator allows interactive creation of Nmap command lines. Scan results can be saved and viewed later. Saved scan results can be compared with one another to see how they differ. The results of recent scans are stored in a searchable database.

You can install zenmap using the following [apt-get command][]:  
`$ sudo apt-get install zenmap`  
Sample outputs:

[sudo] password for vivek: 
    Reading package lists... Done
    Building dependency tree       
    Reading state information... Done
    The following NEW packages will be installed:
      zenmap
    0 upgraded, 1 newly installed, 0 to remove and 11 not upgraded.
    Need to get 616 kB of archives.
    After this operation, 1,827 kB of additional disk space will be used.
    Get:1 http://debian.osuosl.org/debian/ squeeze/main zenmap amd64 5.00-3 [616 kB]
    Fetched 616 kB in 3s (199 kB/s)                       
    Selecting previously deselected package zenmap.
    (Reading database ... 281105 files and directories currently installed.)
    Unpacking zenmap (from .../zenmap_5.00-3_amd64.deb) ...
    Processing triggers for desktop-file-utils ...
    Processing triggers for gnome-menus ...
    Processing triggers for man-db ...
    Setting up zenmap (5.00-3) ...
    Processing triggers for python-central ...

Type the following command to start zenmap:  
`$ sudo zenmap`  
Sample outputs

[![Fig.02: zenmap in action][Fig.02_ zenmap in action]][Fig.02_ zenmap in action_Fig.02_ zenmap in action]

Fig.02: zenmap in action

## How do I detect and block port scanning? ##

Try the following resources:

1.  [How to use psad tool to detect and block port scan attacks in real time][].
2.  [Debian / Ubuntu Linux: Install and Configure Shoreline Firewall (Shorewall)][Debian _ Ubuntu Linux_ Install and Configure Shoreline Firewall _Shorewall].
3.  [CentOS / Redhat Iptables Firewall Configuration Tutorial][CentOS _ Redhat Iptables Firewall Configuration Tutorial].
4.  [Linux: 20 Iptables Examples For New SysAdmins][fully patched server with firewall].
5.  [20 Linux Server Hardening Security Tips][].

References:

*  [The official Nmap project guide to network discovery and security Scanning][].
 *  [The official Nmap project][] home page.

转载于:https://my.oschina.net/u/2306127/blog/2032343

[2019_Python_]: https://my.oschina.net/u/2663968/blog/3061697
[hot3.png]: /images/20220114/e1eafb2fe5db4f1b92d0f75e19cf970e.png
[Command Line Hacks]: https://www.cyberciti.biz/topics/open-source/command-line-hacks/
[Howto]: https://www.cyberciti.biz/topics/howto/
[Networking]: https://www.cyberciti.biz/topics/networking/
[Security]: https://www.cyberciti.biz/topics/security/
[nmap in action]: https://www.cyberciti.biz/media/new/cms/2012/11/welcome-nmap.png
[nmap in action 1]: https://www.cyberciti.biz/networking/nmap-command-examples-tutorials/attachment/welcome-nmap/
[fully patched server with firewall]: https://www.cyberciti.biz/tips/linux-iptables-examples.html
[Debian _ Ubuntu Linux_ Install nmap Software For Scanning Network]: https://www.cyberciti.biz/faq/install-nmap-debian-ubuntu-server-desktop-system/
[CentOS _ RHEL_ Install nmap Network Security Scanner]: https://www.cyberciti.biz/faq/howto-install-nmap-on-centos-rhel-redhat-enterprise-linux/
[OpenBSD_ Install nmap Network Security Scanner]: https://www.cyberciti.biz/faq/installing-nmap-network-port-scanner-under-openbsd-using-pkg_add/
[Fig.01_ nmap output]: https://s0.cyberciti.org/uploads/faq/2012/11/redhat-nmap-command-output.png
[ip command]: https://www.cyberciti.biz/faq/howto-linux-configuring-default-route-with-ipcommand/
[route command]: https://www.cyberciti.biz/faq/what-is-a-routing-table/
[netstat command]: https://www.cyberciti.biz/faq/linux-unix-open-ports/
[identify a remote host apps and OS using the -O option]: https://www.cyberciti.biz/faq/identify-remote-host-by-unix-linux-command/
[Fingerprinting a web-server]: https://www.cyberciti.biz/faq/find-out-remote-webserver-name/
[dns server]: https://www.cyberciti.biz/tips/howto-remotely-determine-dns-server-version.html
[how to block Xmas packkets_ syn-floods and other conman attacks]: https://www.cyberciti.biz/tips/linux-iptables-10-how-to-block-common-attack.html
[decoys are scanning the target network too]: https://www.cyberciti.biz/tips/nmap-hide-ipaddress-with-decoy-ideal-scan.html
[zenmap the official network mapper]: https://nmap.org/zenmap/
[apt-get command]: https://www.cyberciti.biz/tips/linux-debian-package-management-cheat-sheet.html
[Fig.02_ zenmap in action]: https://www.cyberciti.biz/media/new/cms/2012/11/nmap-usage-examples-output.png
[Fig.02_ zenmap in action_Fig.02_ zenmap in action]: https://www.cyberciti.biz/networking/nmap-command-examples-tutorials/attachment/nmap-usage-examples-output/
[How to use psad tool to detect and block port scan attacks in real time]: https://www.cyberciti.biz/faq/linux-detect-port-scan-attacks/
[Debian _ Ubuntu Linux_ Install and Configure Shoreline Firewall _Shorewall]: https://www.cyberciti.biz/faq/debian-ubuntu-linux-shorewall-firewall-configuration/
[CentOS _ Redhat Iptables Firewall Configuration Tutorial]: https://www.cyberciti.biz/faq/rhel-fedorta-linux-iptables-firewall-configuration-tutorial/
[20 Linux Server Hardening Security Tips]: https://www.cyberciti.biz/tips/linux-security.html
[The official Nmap project guide to network discovery and security Scanning]: https://nmap.org/book/toc.html
[The official Nmap project]: https://nmap.org/