Nmap installation on Linux with Real-time Usage Examples

Nmap stands for “Network Mapper“, is one of the best open-source utility available now for network discovery and security auditing. 

Nmap sends packets and analyzes the response it gets to discover hosts and services on a computer network. It is one of the most widely used port scanners available today to help you find open ports and detecting security risks on a network.

This is the first step for an attacker to get information about the network of targets and identify a potential way to launch an attack. An attacker will know about the services running on open ports along with their version, which helps in determining vulnerabilities for the corresponding version.

It is popularly known as System Administrator’s Swiss Army Knife owing its ability to serve multiple purposes – probing computer networks, host discovery, port scan, vulnerability detection, OS detection, version detection, etc. Its cross-platform utility.

If you do not like working in the command-line interface, it is also available in a GUI – Zenmap, the official Nmap Security Scanner GUI.

Installation

We will demonstrate the installation of Nmap on two commonly used Linux distribution – CentOS and Ubuntu. It is available as a package in most Linux distribution’s repository.

Installing Nmap On CentOS 6/7.x

sudo yum install nmap
$sudo yum install nmap Loaded plugins: fastestmirror, security Setting up Install Process Loading mirror speeds from cached hostfile  * base: mirror.vcu.edu  * centos-sclo-rh: mirror.cc.columbia.edu  * centos-sclo-sclo: mirror.rackspace.com  * epel: reflector.westga.edu  * extras: centos5.zswap.net  * updates: mirror.jaleco.com Resolving Dependencies --> Running transaction check ---> Package nmap.x86_64 2:5.51-6.el6 will be installed --> Finished Dependency Resolution  Dependencies Resolved  ======================================================================================================================================================================================================================================================  Package                                                  Arch                                                       Version                                                           Repository                                                Size ====================================================================================================================================================================================================================================================== Installing:  nmap                                                     x86_64                                                     2:5.51-6.el6                                                      base                                                     2.8 M  Transaction Summary ====================================================================================================================================================================================================================================================== Install       1 Package(s)  Total download size: 2.8 M Installed size: 9.7 M Is this ok [y/N]:
Is this ok [y/N]: y Downloading Packages: nmap-5.51-6.el6.x86_64.rpm                                                                                                                                                                                                     | 2.8 MB     00:00      Running rpm_check_debug Running Transaction Test Transaction Test Succeeded Running Transaction   Installing : 2:nmap-5.51-6.el6.x86_64                                                                                                                                                                                                           1/1    Verifying  : 2:nmap-5.51-6.el6.x86_64                                                                                                                                                                                                           1/1   Installed:   nmap.x86_64 2:5.51-6.el6                                                                                                                                                                                                                              Complete! $
$nmap -version  Nmap version 5.51 ( http://nmap.org )

Installing Nmap on CentOS 8.x

$sudo dnf install nmap -y Last metadata expiration check: 0:58:54 ago on Fri 18 Sep 2020 07:04:54 PM UTC. Dependencies resolved. ======================================================================================================================================================================================================================================================  Package                                                    Architecture                                            Version                                                          Repository                                                  Size ====================================================================================================================================================================================================================================================== Installing:  nmap                                                       x86_64                                                  2:7.70-5.el8                                                     AppStream                                                  5.8 M Installing dependencies:  nmap-ncat                                                  x86_64                                                  2:7.70-5.el8                                                     AppStream                                                  237 k  Transaction Summary ====================================================================================================================================================================================================================================================== Install  2 Packages  Total download size: 6.1 M Installed size: 25 M Downloading Packages: (1/2): nmap-ncat-7.70-5.el8.x86_64.rpm                                                                                                                                                                                669 kB/s | 237 kB     00:00     (2/2): nmap-7.70-5.el8.x86_64.rpm                                                                                                                                                                                     9.2 MB/s | 5.8 MB     00:00     ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ Total                                                                                                                                                                                                                 8.0 MB/s | 6.1 MB     00:00      Running transaction check Transaction check succeeded. Running transaction test Transaction test succeeded. Running transaction   Preparing        :                                                                                                                                                                                                                              1/1    Installing       : nmap-ncat-2:7.70-5.el8.x86_64                                                                                                                                                                                                1/2    Running scriptlet: nmap-ncat-2:7.70-5.el8.x86_64                                                                                                                                                                                                1/2    Installing       : nmap-2:7.70-5.el8.x86_64                                                                                                                                                                                                     2/2    Running scriptlet: nmap-2:7.70-5.el8.x86_64                                                                                                                                                                                                     2/2    Verifying        : nmap-2:7.70-5.el8.x86_64                                                                                                                                                                                                     1/2    Verifying        : nmap-ncat-2:7.70-5.el8.x86_64                                                                                                                                                                                                2/2   Installed:   nmap-2:7.70-5.el8.x86_64                                                                                                nmap-ncat-2:7.70-5.el8.x86_64                                                                                                 Complete! $

With -y option, DNF/YUM will install the specified package without asking for confirmation.

DNF(Dandified Yum) is the new package manager in RHEL/CentOS 8 which can be used to install packages. It is the next-generation version of the YUM( Yellowdog Updater Modified) and intended to be a substitution of YUM in RPM-based systems.

$nmap -version Nmap version 7.70 ( https://nmap.org ) Platform: x86_64-redhat-linux-gnu Compiled with: liblua-5.3.3 openssl-1.1.1 libpcre-8.42 libpcap-1.9.0-PRE-GIT nmap-libdnet-1.12 ipv6 Compiled without: libssh2 libz Available nsock engines: epoll poll select

Ubuntu

sudo apt-get update
$sudo apt-get install nmap -y Reading package lists... Done Building dependency tree        Reading state information... Done The following package was automatically installed and is no longer required:   libnuma1 Use 'sudo apt autoremove' to remove it. The following additional packages will be installed:   libblas3 liblinear4 liblua5.3-0 lua-lpeg nmap-common Suggested packages:   liblinear-tools liblinear-dev ncat ndiff zenmap The following NEW packages will be installed:   libblas3 liblinear4 liblua5.3-0 lua-lpeg nmap nmap-common 0 upgraded, 6 newly installed, 0 to remove and 30 not upgraded. Need to get 5669 kB of archives. After this operation, 26.8 MB of additional disk space will be used. Get:1 http://us-west1.gce.archive.ubuntu.com/ubuntu focal/main amd64 libblas3 amd64 3.9.0-1build1 [142 kB] Get:2 http://us-west1.gce.archive.ubuntu.com/ubuntu focal/universe amd64 liblinear4 amd64 2.3.0+dfsg-3build1 [41.7 kB] Get:3 http://us-west1.gce.archive.ubuntu.com/ubuntu focal/main amd64 liblua5.3-0 amd64 5.3.3-1.1ubuntu2 [116 kB] Get:4 http://us-west1.gce.archive.ubuntu.com/ubuntu focal/universe amd64 lua-lpeg amd64 1.0.2-1 [31.4 kB] Get:5 http://us-west1.gce.archive.ubuntu.com/ubuntu focal/universe amd64 nmap-common all 7.80+dfsg1-2build1 [3676 kB] Get:6 http://us-west1.gce.archive.ubuntu.com/ubuntu focal/universe amd64 nmap amd64 7.80+dfsg1-2build1 [1662 kB] Fetched 5669 kB in 1s (7683 kB/s) Selecting previously unselected package libblas3:amd64. (Reading database ... 62831 files and directories currently installed.) Preparing to unpack .../0-libblas3_3.9.0-1build1_amd64.deb ... Unpacking libblas3:amd64 (3.9.0-1build1) ... Selecting previously unselected package liblinear4:amd64. Preparing to unpack .../1-liblinear4_2.3.0+dfsg-3build1_amd64.deb ... Unpacking liblinear4:amd64 (2.3.0+dfsg-3build1) ... Selecting previously unselected package liblua5.3-0:amd64. Preparing to unpack .../2-liblua5.3-0_5.3.3-1.1ubuntu2_amd64.deb ... Unpacking liblua5.3-0:amd64 (5.3.3-1.1ubuntu2) ... Selecting previously unselected package lua-lpeg:amd64. Preparing to unpack .../3-lua-lpeg_1.0.2-1_amd64.deb ... Unpacking lua-lpeg:amd64 (1.0.2-1) ... Selecting previously unselected package nmap-common. Preparing to unpack .../4-nmap-common_7.80+dfsg1-2build1_all.deb ... Unpacking nmap-common (7.80+dfsg1-2build1) ... Selecting previously unselected package nmap. Preparing to unpack .../5-nmap_7.80+dfsg1-2build1_amd64.deb ... Unpacking nmap (7.80+dfsg1-2build1) ... Setting up lua-lpeg:amd64 (1.0.2-1) ... Setting up libblas3:amd64 (3.9.0-1build1) ... update-alternatives: using /usr/lib/x86_64-linux-gnu/blas/libblas.so.3 to provide /usr/lib/x86_64-linux-gnu/libblas.so.3 (libblas.so.3-x86_64-linux-gnu) in auto mode Setting up nmap-common (7.80+dfsg1-2build1) ... Setting up liblua5.3-0:amd64 (5.3.3-1.1ubuntu2) ... Setting up liblinear4:amd64 (2.3.0+dfsg-3build1) ... Setting up nmap (7.80+dfsg1-2build1) ... Processing triggers for man-db (2.9.1-1) ... Processing triggers for libc-bin (2.31-0ubuntu9) ...
$nmap -version Nmap version 7.80 ( https://nmap.org ) Platform: x86_64-pc-linux-gnu Compiled with: liblua-5.3.3 openssl-1.1.1d nmap-libssh2-1.8.2 libz-1.2.11 libpcre-8.39 libpcap-1.9.1 nmap-libdnet-1.12 ipv6 Compiled without: Available nsock engines: epoll poll select

Real-time Nmap Usage Example

We will see a few examples illustrating the usage of the Nmap command.

Scan for open ports

Syntax for nmap

nmap [Scan Type(s)] [Options] {target specification}

Target specification could be a hostname, IP address, domain name, network, subnet, etc.

Scan a domain

nmap scanme.nmap.org
$nmap scanme.nmap.org Starting Nmap 7.80 ( https://nmap.org ) at 2020-09-18 20:14 UTC Nmap scan report for scanme.nmap.org (45.33.32.156) Host is up (0.025s latency). Other addresses for scanme.nmap.org (not scanned): 2600:3c01::f03c:91ff:fe18:bb2f Not shown: 995 closed ports PORT      STATE    SERVICE 22/tcp    open     ssh 25/tcp    filtered smtp 80/tcp    open     http 9929/tcp  open     nping-echo 31337/tcp open     Elite  Nmap done: 1 IP address (1 host up) scanned in 1.73 seconds

With no flags, Nmap will, by default –

We could see four open ports, one filtered port, and 995 closed ports in the output shown above. A port that cannot be determined by Nmap if it is closed or open, which may be due to a firewall, is filtered.

Here in the example shown above, we scan scanme.nmap.com, which has authorized itself to be scanned.

nmap -F scanme.nmap.org

You could also use the fast scan option -F to scan only the top 100 most commonly used ports of each protocol it is asked to scan.

Scan IP address

nmap 192.168.0.7
$nmap 192.168.0.7 Starting Nmap 7.80 ( https://nmap.org ) at 2020-09-18 20:12 UTC Nmap scan report for server-1.geekflare.com (192.168.0.7) Host is up (0.034s latency). Not shown: 999 closed ports PORT   STATE SERVICE 22/tcp open  ssh  Nmap done: 1 IP address (1 host up) scanned in 0.62 seconds

Scan a subnet

nmap 192.168.0.0/24
$nmap 192.168.0.0/24 Starting Nmap 7.80 ( https://nmap.org ) at 2020-09-18 20:15 UTC Nmap scan report for server-1.geekflare.com (192.168.0.7) Host is up (0.044s latency). Not shown: 999 closed ports PORT   STATE SERVICE 22/tcp open  ssh  Nmap scan report for server-2.geekflare.com (192.168.0.8) Host is up (0.046s latency). Not shown: 999 closed ports PORT   STATE SERVICE 22/tcp open  ssh  Nmap scan report for server-3.geekflare.com (192.168.0.9) Host is up (0.043s latency). Not shown: 999 closed ports PORT   STATE SERVICE 22/tcp open  ssh  Nmap scan report for server-4.geekflare.com (192.168.0.10) Host is up (0.044s latency). Not shown: 999 closed ports PORT   STATE SERVICE 22/tcp open  ssh  Nmap done: 256 IP addresses (4 hosts up) scanned in 4.67 seconds

Scanning multiple hosts

Scanning multiple hosts is easy!

nmap 192.168.0.1 192.168.0.3 192.168.0.4

Above mentioned command could also be written as below to avoid mentioning the IP address again

nmap 192.168.0.1,3,4
nmap 192.168.0.1-20

The above command will scan the first twenty hosts of the sub-network.

nmap 192.168.0.*

The above command will scan for all 256 IP addresses in the subnet.

You could specify all the hosts required to be scanned in a file and use the command below –

nmap -iL /tmp/hostfile

Example of host file –

cat /tmp/hostfile  192.168.0.1,2,4  scanme.nmap.org  10.0.0-255.1-254

You could exclude a few hosts from a group search if you want.

nmap 192.168.0.* --exclude 192.168.0.2  nmap 192.168.0.1-40 --exclude 192.168.0.5,6,7

You could also exclude hosts from your search using the –excludefile flag

nmap 192.168.0.* --excludefile /tmp/hosts.txt

Nmap Port Selection

To scan specific ports on a system, instead of the default top 1000 commonly used ports, you could use -p parameter. 

nmap -p 22,80,443 192.168.0.2-50
$nmap -p 22,80,443 192.168.0.2-50 Starting Nmap 7.70 ( https://nmap.org ) at 2020-09-18 20:18 UTC Nmap scan report for server-1.geekflare.com (192.168.0.7) Host is up (0.00018s latency).  PORT    STATE  SERVICE 22/tcp  open   ssh 80/tcp  closed http 443/tcp closed https  Nmap scan report for server-2.geekflare.com (192.168.0.8) Host is up (0.00094s latency).  PORT    STATE  SERVICE 22/tcp  open   ssh 80/tcp  closed http 443/tcp closed https  Nmap scan report for server-3.geekflare.com (192.168.0.9) Host is up (0.00092s latency).  PORT    STATE  SERVICE 22/tcp  open   ssh 80/tcp  closed http 443/tcp closed https  Nmap scan report for server-4.geekflare.com (192.168.0.10) Host is up (0.00089s latency).  PORT    STATE  SERVICE 22/tcp  open   ssh 80/tcp  closed http 443/tcp closed https  Nmap done: 49 IP addresses (4 hosts up) scanned in 1.65 seconds

The above command will scan only for ports 22, 80, and 443 on the IP addresses mentioned.

nmap -p 1-500 192.168.0.2

The above command will scan for ports 1 to 500 on the host mentioned.

nmap -p- 192.168.0.2

Using -p- will scan all 65535 ports.

Redirecting output to a file

By default, Nmap prints the output on the terminal, but when scanning a large network, it is better to save the results in a file for better analysis. You can save the results of its scans in different file formats.

Normal output format [-oN]

Normal mode will give you the output as you see it on your screen.

nmap -oN /tmp/scanResult.txt 192.168.0.0/24

XML output format [-oX]

We could export the results in XML format. It is one of the most used file formats as most programming languages have libraries for XML parsing.

nmap -oX /tmp/scanResult.xml 192.168.0.0/24

Grepable Output format [-oG]

We get the output in a format that is very easily used with the grep command. The output could later be fed to command-line utilities like – awk, grep, sed to perform additional operations as required.

nmap -oG /tmp/scanResult.txt 192.168.0.0/24

Script kiddie output [-oS]

It uses the “leet”, replacing letters with their visually alike number representations. This output format is not useful for any particular case and was included only as a joke.

nmap -oS /tmp/scanResult scanme.nmap.org
$nmap -oS /tmp/scanResult scanme.nmap.org Starting Nmap 7.70 ( https://nmap.org ) at 2020-09-18 20:34 UTC Nmap scan report for scanme.nmap.org (45.33.32.156) Host is up (0.053s latency). Other addresses for scanme.nmap.org (not scanned): 2600:3c01::f03c:91ff:fe18:bb2f Not shown: 995 closed ports PORT      STATE    SERVICE 22/tcp    open     ssh 25/tcp    filtered smtp 80/tcp    open     http 9929/tcp  open     nping-echo 31337/tcp open     Elite  Nmap done: 1 IP address (1 host up) scanned in 2.12 seconds $ $cat /tmp/scanResult $tart|Ng Nmap 7.70 ( httpz://NmAp.oRg ) aT 2020-09-18 20:34 UTc Nmap $can rEp0rt f0r Scanm3.nmap.0rg (45.33.32.156) H0st iS up (0.053s lat3ncy). Other addreSSes for $canm3.nmap.0Rg (n0t scanN3D): 2600:3c01::f03c:91ff:fE18:bb2f Not sh0wn: 995 clOs3d p0rtS P0rT      $TAT3    S3RV|C3 22/TCp    op3n     Ssh 25/tcp    f1ltEr3d $mtp 80/tCp    op3n     http 9929/tcp  Open     Nping-ech0 31337/tCP 0pen     3litE  Nmap d0n3: 1 Ip addRe$s (1 hO$t up) $CANN3d In 2.12 s3C0nDz

Various Nmap scan types

TCP Connect Scan [-sT]

This is the basic form of TCP scanning and involves no stealth. It attempts to establish a complete connection with the range ports specified with a complete three-way handshake exchange (SYN -> SYN/ACK -> ACK). A successful connection indicates an open port.

This is the default scan type Nmap uses when executed by an unprivileged user.

nmap -sT 192.168.0.1
$nmap -sT 192.168.0.7 Starting Nmap 7.70 ( https://nmap.org ) at 2020-09-18 19:52 UTC Nmap scan report for server-1.geekflare.com (192.168.0.7) Host is up (0.00042s latency). Not shown: 999 closed ports PORT   STATE SERVICE 22/tcp open  ssh  Nmap done: 1 IP address (1 host up) scanned in 0.09 seconds

TCP SYN Scan [-sS]

Also known as a half-open scan, it is stealthier than TCP connect scan as it never establishes a complete connection. TCP SYN scan is the default scan type when executed as a privileged user, and unprivileged users will not have the permission to run this scan as it requires privileges to raw socket / raw packet.

nmap -sS 192.168.0.1
$sudo nmap -sS 192.168.0.7 Starting Nmap 7.70 ( https://nmap.org ) at 2020-09-18 19:51 UTC Nmap scan report for server-1.geekflare.com (192.168.0.7) Host is up (0.00022s latency). Not shown: 999 closed ports PORT   STATE SERVICE 22/tcp open  ssh  Nmap done: 1 IP address (1 host up) scanned in 1.50 seconds
$nmap -sS 192.168.0.1 You requested a scan type which requires root privileges. QUITTING!

As we could see in the example above, an SYN scan could not be executed with non-privileged users.

UDP scan [-sU]

If no flag is specified, by default, Nmap scans for TCP ports. To scan for UDP port we have to use the -sU flag, as shown below.

$sudo nmap -sU 192.168.0.8 Starting Nmap 7.70 ( https://nmap.org ) at 2020-09-18 19:44 UTC Nmap scan report for server-2.geekflare.com (192.168.0.8) Host is up (0.00036s latency). Not shown: 999 closed ports PORT     STATE         SERVICE 5355/udp open|filtered llmnr  Nmap done: 1 IP address (1 host up) scanned in 999.27 seconds

Ping Scan [-sn]

This is highly useful when you only need to know whether the host is alive or not and do not need information about open ports on the hosts.

This is often referred to as ‘Ping sweep’. In previously released versions of Nmap, -sn was known as -sP.

nmap -sn 192.168.1.0/24
$nmap -sn 192.168.1.0/24 Starting Nmap 7.70 ( https://nmap.org ) at 2020-09-18 19:39 UTC Nmap scan report for server-7.geekflare.com (192.168.1.2) Host is up (0.033s latency). Nmap scan report for server-10.geekflare.com (192.168.1.3) Host is up (0.035s latency). Nmap scan report for server-13.geekflare.com (192.168.1.4) Host is up (0.10s latency). Nmap done: 256 IP addresses (3 hosts up) scanned in 9.85 seconds

In the above example, we could see, in the specified target subnet, out of 256 IP addresses scanned, only three hosts are up.

nmap -sn -n -v 192.168.0.0/24 -oG - | grep -iv down

-sn –> Ping scan.

-n –> Ignore the DNS resolution and speed up the scan.

-v –> Add verbose to get more information of scan.

-oG –> Provides the output in grepable format.

- –> Hyphen redirects the grepable output to standard output, which is then piped to grep.

-iv –> Ignore the lines having the word ‘down’.

$nmap -sn -n -v 192.168.0.0/24 -oG - | grep -iv down # Nmap 7.70 scan initiated Fri Sep 18 19:40:17 2020 as: nmap -sn -n -v -oG - 192.168.0.0/24 # Ports scanned: TCP(0;) UDP(0;) SCTP(0;) PROTOCOLS(0;) Host: 192.168.0.7 ()    Status: Up Host: 192.168.0.8 ()    Status: Up Host: 192.168.0.9 ()    Status: Up Host: 192.168.0.10 ()   Status: Up # Nmap done at Fri Sep 18 19:40:20 2020 -- 256 IP addresses (4 hosts up) scanned in 2.91 seconds

We could see only four hosts are alive out of 256 IP addresses scanned in the subnet.

OS and Service Version Detection

OS Scanning

In addition to port scanning and host discovery, Nmap could also provide information about the underlying operating system. Nmap has one of the largest operating system fingerprint databases and can identify operating systems by analyzing their response to TCP/IP probes.

It could be enabled with the -O flag. Below is the command –

nmap -O localhost
$sudo nmap -O localhost Starting Nmap 7.70 ( https://nmap.org ) at 2020-09-18 19:32 UTC Nmap scan report for localhost (127.0.0.1) Host is up (0.000012s latency). Other addresses for localhost (not scanned): ::1 Not shown: 999 closed ports PORT   STATE SERVICE 22/tcp open  ssh Device type: general purpose Running: Linux 3.X OS CPE: cpe:/o:linux:linux_kernel:3 OS details: Linux 3.7 - 3.10 Network Distance: 0 hops  OS detection performed. Please report any incorrect results at https://nmap.org/submit/ . Nmap done: 1 IP address (1 host up) scanned in 3.89 seconds

Version Scanning

Nmap also helps scanning services running and their version information from open ports. This is helpful in scanning services running on vulnerable versions and could be updated to mitigate the risk.

It could be enabled with -sV

nmap -sV localhost
$sudo nmap -sV localhost Starting Nmap 7.70 ( https://nmap.org ) at 2020-09-18 19:35 UTC Nmap scan report for localhost (127.0.0.1) Host is up (0.000010s latency). Other addresses for localhost (not scanned): ::1 Not shown: 999 closed ports PORT   STATE SERVICE VERSION 22/tcp open  ssh     OpenSSH 8.0 (protocol 2.0)  Service detection performed. Please report any incorrect results at https://nmap.org/submit/ . Nmap done: 1 IP address (1 host up) scanned in 1.96 seconds

Aggressive Scan

Nmap performs an aggressive and advanced scan as well that enables OS detection -O, script scanning -sC, version scanning -sV, and traceroute --traceroute.

We could pass -A argument to perform an aggressive scan.

$sudo nmap -A scanme.nmap.org Starting Nmap 7.70 ( https://nmap.org ) at 2020-09-18 20:26 UTC Nmap scan report for scanme.nmap.org (45.33.32.156) Host is up (0.051s latency). Other addresses for scanme.nmap.org (not scanned): 2600:3c01::f03c:91ff:fe18:bb2f Not shown: 995 closed ports PORT      STATE    SERVICE    VERSION 22/tcp    open     ssh        OpenSSH 6.6.1p1 Ubuntu 2ubuntu2.13 (Ubuntu Linux; protocol 2.0) | ssh-hostkey:  |   1024 ac:00:a0:1a:82:ff:cc:55:99:dc:67:2b:34:97:6b:75 (DSA) |   2048 20:3d:2d:44:62:2a:b0:5a:9d:b5:b3:05:14:c2:a6:b2 (RSA) |   256 96:02:bb:5e:57:54:1c:4e:45:2f:56:4c:4a:24:b2:57 (ECDSA) |_  256 33:fa:91:0f:e0:e1:7b:1f:6d:05:a2:b0:f1:54:41:56 (ED25519) 25/tcp    filtered smtp 80/tcp    open     http       Apache httpd 2.4.7 ((Ubuntu)) |_http-server-header: Apache/2.4.7 (Ubuntu) |_http-title: Go ahead and ScanMe! 9929/tcp  open     nping-echo Nping echo 31337/tcp open     tcpwrapped Aggressive OS guesses: Linux 2.6.32 (94%), Linux 3.2 - 4.9 (94%), Linux 2.6.32 - 3.10 (94%), Linux 3.4 - 3.10 (93%), Linux 3.1 (92%), Linux 3.2 (92%), Linux 3.3 (92%), Synology DiskStation Manager 5.2-5644 (92%), Netgear RAIDiator 4.2.28 (92%), AXIS 210A or 211 Network Camera (Linux 2.6.17) (92%) No exact OS matches for host (test conditions non-ideal). Network Distance: 7 hops Service Info: OS: Linux; CPE: cpe:/o:linux:linux_kernel  TRACEROUTE (using port 143/tcp) HOP RTT      ADDRESS 1   48.15 ms 72.14.239.197 2   52.74 ms 209.85.253.9 3   49.54 ms 142.250.234.59 4   49.99 ms 108.170.242.251 5   50.70 ms 213.52.131.176 6   50.85 ms 173.230.159.71 7   53.40 ms scanme.nmap.org (45.33.32.156)  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 259.05 seconds $$sudo nmap -A scanme.nmap.org Starting Nmap 7.70 ( https://nmap.org ) at 2020-09-18 20:33 UTC Stats: 0:00:00 elapsed; 0 hosts completed (0 up), 0 undergoing Script Pre-Scan NSE Timing: About 0.00% done

Legal issues with port scanning

It is always advisable to get written authorization/permission from the owner of the target network before initializing any scan.

For example –  http://scanme.nmap.org/ has authorized itself to be scanned. You could read in detail on the official website.

What’s next?

Check out how to install Nmap on Windows.