This guide explains different methods to check for open ports on your Webdock server. An open port is a port on which some process or application is running and it can accept data. In this guide we will use different tools to find out which ports are open. Show
An open port is defined as a port which has a service listening and accepting connections. You may find that you have services listening on ports which despite this are not accessible from the internet. This is what your firewall does: Block access to ports which you haven't explicitly allowed access to. For a guide on managing your firewall, take a look at our UFW guide here. Prerequisites
The difference between addressesIt matters whether a service is listening to a port on 127.0.0.1 (localhost) or if it is listening on 0.0.0.0 - typically what this means is that a service listening on localhost is only accessible from the host machine itself and not the wider internet. If you see a service listening on all interfaces (*) or 0.0.0.0 then the service is accessible from the internet - unless actively firewalled, which you will need to check for in Iptables or by running "ufw status" if you use UFW to manage your firewall. Check for open ports using nmapNetwork mapper or nmap is an open source tool used to scan networks and find open ports on a host. The following command will scan all the ports on the host. $ sudo nmap localhost Starting Nmap 7.80 ( https://nmap.org ) at 2021-06-12 06:03 UTC Nmap scan report for localhost (127.0.0.1) Host is up (0.0000090s latency). Not shown: 995 closed ports PORT STATE SERVICE 21/tcp open ftp 22/tcp open ssh 80/tcp open http 443/tcp open https 3306/tcp open mysql Nmap done: 1 IP address (1 host up) scanned in 0.23 secondsIn order to check a specific port whether it is open or not, use the -p option to specify the port. $ sudo nmap -p 80 localhost Starting Nmap 7.80 ( https://nmap.org ) at 2021-06-12 06:04 UTC Nmap scan report for localhost (127.0.0.1) Host is up (0.000054s latency). PORT STATE SERVICE 80/tcp open http Nmap done: 1 IP address (1 host up) scanned in 0.18 secondsBe careful using nmap as if you accidentally start scanning the entire network, you risk that your IP address will be banned. Check for open ports using lsofThe lsof (list open files) command, as name suggests, is used to list all the open files in linux. These files may be network sockets, disk files or devices opened by different processes. Use the lsof command along with the -nP options to list all open sockets. $ sudo lsof -nP | grep LISTEN ...snip... redis-ser 511 513 redis-ser redis 6u IPv4 662257788 0t0 TCP 127.0.0.1:6379 (LISTEN) redis-ser 511 513 redis-ser redis 7u IPv6 662257789 0t0 TCP [::1]:6379 (LISTEN) redis-ser 511 515 redis-ser redis 6u IPv4 662257788 0t0 TCP 127.0.0.1:6379 (LISTEN) redis-ser 511 515 redis-ser redis 7u IPv6 662257789 0t0 TCP [::1]:6379 (LISTEN) redis-ser 511 517 redis-ser redis 6u IPv4 662257788 0t0 TCP 127.0.0.1:6379 (LISTEN) redis-ser 511 517 redis-ser redis 7u IPv6 662257789 0t0 TCP [::1]:6379 (LISTEN) ...snip...List only the TCP open sockets. $ sudo lsof -i tcp ...snip... pure-ftpd 303 root 4u IPv4 662259745 0t0 TCP *:ftp (LISTEN) pure-ftpd 303 root 5u IPv6 662259746 0t0 TCP *:ftp (LISTEN) sshd 304 root 3u IPv4 662258731 0t0 TCP *:ssh (LISTEN) sshd 304 root 4u IPv6 662258733 0t0 TCP *:ssh (LISTEN) ..snip...For UDP open sockets, use the following command. $ sudo lsof -i udpsystemd-r 254 systemd-resolve 12u IPv4 662203276 0t0 UDP localhost:domainCheck for open ports using netstatThe netstat (network statistic) command can be used to monitor and scan networks. Get a list of all tcp and udp open ports using the netstat command. $ sudo netstat -l ...snip... tcp 0 0 localhost:27017 0.0.0.0:* LISTEN tcp 0 0 localhost:mysql 0.0.0.0:* LISTEN tcp 0 0 localhost:6379 0.0.0.0:* LISTEN tcp 0 0 localhost:11211 0.0.0.0:* LISTEN ...snip...List TCP ports only. $ sudo netstat -lt ...snip... tcp 0 0 localhost:27017 0.0.0.0:* LISTEN tcp 0 0 localhost:mysql 0.0.0.0:* LISTEN tcp 0 0 localhost:6379 0.0.0.0:* LISTEN tcp 0 0 localhost:11211 0.0.0.0:* LISTEN tcp 0 0 0.0.0.0:http 0.0.0.0:* LISTEN tcp6 0 0 [::]:ftp [::]:* LISTEN tcp6 0 0 [::]:ssh [::]:* LISTEN ...snip...For UDP ports only. $ sudo netstat -lu Active Internet connections (only servers) Proto Recv-Q Send-Q Local Address Foreign Address State udp 0 0 localhost:domain 0.0.0.0:*Check open ports using ssThe ss command is used to list detailed information of the network sockets. It provides more detailed information than the netstat command. List all the listening ports on a linux system. $ sudo ss -l Netid State Recv-Q Send-Q Local Address:Port Peer Address:Port Process nl UNCONN 0 0 rtnl:systemd/1 * nl UNCONN 0 0 rtnl:kernel * nl UNCONN 0 0 rtnl:systemd-resolve/254 * nl UNCONN 0 0 rtnl:systemd-resolve/254 * nl UNCONN 0 0 rtnl:systemd/1 * ...snip...To list only TCP listening ports, use the -lt flag. $ sudo ss -lt ...snip... LISTEN 0 128 0.0.0.0:ssh 0.0.0.0:* LISTEN 0 511 0.0.0.0:https 0.0.0.0:* LISTEN 0 4096 127.0.0.1:27017 0.0.0.0:* LISTEN 0 70 127.0.0.1:mysql 0.0.0.0:* LISTEN 0 511 127.0.0.1:6379 0.0.0.0:* ...snip...For UDP listening ports, use the -lu flag. $ sudo ss -lu State Recv-Q Send-Q Local Address:Port Peer Address:Port Process UNCONN 0 0 127.0.0.53%lo:domain 0.0.0.0:*ConclusionThere are different tools available to monitor open ports on your server. In this guide we discussed how we can check for open ports on Webdock server using different command line tools like nmap, ss, netstat and lsof. What command could you use to display listening TCP ports on a Linux system?You can use the ss command to display open ports via listening sockets. This will print all listening sockets ( -l ) along with the port number ( -n ), with TCP ports ( -t ) and UDP ports ( -u ) also listed in the output.
Which of the following command should you use to locate open ports?Which of the following commands should you use to locate open ports? Use nmap to locate open ports. Open ports can provide information about which operating system a computer uses and might provide entry points or information about ways to formulate an attack.
How check TCP connection in Linux?Check TCP Connection Status in Linux
To display listeners and connections on Linux we can use the netstat or ss command. While older Linux boxes only support netstat, newer Linux distributions use netstat and ss in parallel.
How do I check if a port is open on a Linux remote?The following commands can be used to check if a port is open on the remote server in Linux.. Use nc command nc -zvw10 192.168.0.1 22.. Use nmap command nmap 192.168.0.1 -p 22.. Use telnet command telnet 192.168.0.1 22.. Use python telnet module.. Use python socket module.. Use curl command.. |
