How to find Operating System of a remote computer using nmap?

Nmap is a network exploration and security auditing tool. It can be used to identify hosts and services on a network, as well as security issues. Nmap can be used to scan for vulnerable open ports on systems.

To identify Operating System on a remote server or computer, you can use the command

sudo nmap -O REMOTE_COMPUTER_IP

Example

boby@sok-01:~$ sudo nmap -O ok.serverok.in
Starting Nmap 7.80 ( https://nmap.org ) at 2022-09-18 03:03 IST
Nmap scan report for ok.serverok.in (51.38.246.115)
Host is up (0.18s latency).
rDNS record for 51.38.246.115: ok
Not shown: 984 closed ports
PORT      STATE    SERVICE
23/tcp    filtered telnet
25/tcp    filtered smtp
80/tcp    open     http
135/tcp   filtered msrpc
139/tcp   filtered netbios-ssn
443/tcp   open     https
445/tcp   filtered microsoft-ds
593/tcp   filtered http-rpc-epmap
1900/tcp  filtered upnp
2323/tcp  filtered 3d-nfsd
3005/tcp  filtered deslogin
3333/tcp  open     dec-notes
5555/tcp  filtered freeciv
10001/tcp open     scp-config
50002/tcp filtered iiimsf
52869/tcp filtered unknown
Aggressive OS guesses: HP P2000 G3 NAS device (90%), Linux 2.6.32 (89%), Linux 2.6.32 - 3.1 (89%), Ubiquiti AirOS 5.5.9 (89%), Ubiquiti Pico Station WAP (AirOS 5.2.6) (88%), Linux 2.6.32 - 3.13 (88%), Linux 3.0 - 3.2 (88%), Infomir MAG-250 set-top box (88%), Linux 3.7 (88%), Netgear RAIDiator 4.2.21 (Linux 2.6.37) (88%)
No exact OS matches for host (test conditions non-ideal).
Network Distance: 18 hops

OS detection performed. Please report any incorrect results at https://nmap.org/submit/ .
Nmap done: 1 IP address (1 host up) scanned in 10.94 seconds
boby@sok-01:~$ 

See nmap