- TL;DR: lsof -ti tcp:3000 -sTCP:LISTEN xargs kill If you're in a situation where there are both clients and servers using the port, e.g.: $ lsof -i tcp:3000 COMMAND PID USER FD TYPE DEVICE SIZE/OFF NODE NAME node 2043 benjiegillam 21u IPv4 0xb1b4330c68e5ad61 0t0 TCP localhost:3000-localhost:52557 (ESTABLISHED) node 2043 benjiegillam 22u IPv4 0xb1b4330c8d393021 0t0 TCP localhost:3000.
- If it's No, it's a 32-bit app, and you need to upgrade it before using macOS 10.15. Find 32-bit apps on your Mac through Activity Monitor.
Today I found an easy way to check which application is using which port in my system. Here I'm sharing the steps. These steps are applicable for the Windows Operating System. Checking which application is using a port: Open the command prompt - start » run » cmd or start » All Programs » Accessories » Command Prompt.
By Rick Anderson
This document shows how to:
- Require HTTPS for all requests.
- Redirect all HTTP requests to HTTPS.
No API can prevent a client from sending sensitive data on the first request.
Warning
API projects
Do not use RequireHttpsAttribute on Web APIs that receive sensitive information. RequireHttpsAttribute uses HTTP status codes to redirect browsers from HTTP to HTTPS. API clients may not understand or obey redirects from HTTP to HTTPS. Such clients may send information over HTTP. Web APIs should either:
- Not listen on HTTP.
- Close the connection with status code 400 (Bad Request) and not serve the request.
HSTS and API projects
The default API projects don't include HSTS because HSTS is generally a browser only instruction. Other callers, such as phone or desktop apps, do not obey the instruction. Even within browsers, a single authenticated call to an API over HTTP has risks on insecure networks. The secure approach is to configure API projects to only listen to and respond over HTTPS.
Warning
API projects
Do not use RequireHttpsAttribute on Web APIs that receive sensitive information. RequireHttpsAttribute uses HTTP status codes to redirect browsers from HTTP to HTTPS. API clients may not understand or obey redirects from HTTP to HTTPS. Such clients may send information over HTTP. Web APIs should either:
- Not listen on HTTP.
- Close the connection with status code 400 (Bad Request) and not serve the request.
Require HTTPS
We recommend that production ASP.NET Core web apps use:
- HTTPS Redirection Middleware (UseHttpsRedirection) to redirect HTTP requests to HTTPS.
- HSTS Middleware (UseHsts) to send HTTP Strict Transport Security Protocol (HSTS) headers to clients.
Note
Apps deployed in a reverse proxy configuration allow the proxy to handle connection security (HTTPS). If the proxy also handles HTTPS redirection, there's no need to use HTTPS Redirection Middleware. If the proxy server also handles writing HSTS headers (for example, native HSTS support in IIS 10.0 (1709) or later), HSTS Middleware isn't required by the app. For more information, see Opt-out of HTTPS/HSTS on project creation.
UseHttpsRedirection
The following code calls UseHttpsRedirection in the Startup class:
The preceding highlighted code:
- Uses the default HttpsRedirectionOptions.RedirectStatusCode (Status307TemporaryRedirect).
- Uses the default HttpsRedirectionOptions.HttpsPort (null) unless overridden by the
ASPNETCORE_HTTPS_PORTenvironment variable or IServerAddressesFeature.
We recommend using temporary redirects rather than permanent redirects. Link caching can cause unstable behavior in development environments. If you prefer to send a permanent redirect status code when the app is in a non-Development environment, see the Configure permanent redirects in production section. We recommend using HSTS to signal to clients that only secure resource requests should be sent to the app (only in production).
Port configuration
A port must be available for the middleware to redirect an insecure request to HTTPS. If no port is available:
- Redirection to HTTPS doesn't occur.
- The middleware logs the warning 'Failed to determine the https port for redirect.'
Specify the HTTPS port using any of the following approaches:
- Set HttpsRedirectionOptions.HttpsPort.
Set the
https_porthost setting:In host configuration.
By setting the
ASPNETCORE_HTTPS_PORTenvironment variable.By adding a top-level entry in appsettings.json:
Indicate a port with the secure scheme using the ASPNETCORE_URLS environment variable. The environment variable configures the server. The middleware indirectly discovers the HTTPS port via IServerAddressesFeature. This approach doesn't work in reverse proxy deployments.
Set the
https_porthost setting:In host configuration.
By setting the
ASPNETCORE_HTTPS_PORTenvironment variable.By adding a top-level entry in appsettings.json:
Indicate a port with the secure scheme using the ASPNETCORE_URLS environment variable. The environment variable configures the server. The middleware indirectly discovers the HTTPS port via IServerAddressesFeature. This approach doesn't work in reverse proxy deployments.
In development, set an HTTPS URL in launchsettings.json. Enable HTTPS when IIS Express is used.
Configure an HTTPS URL endpoint for a public-facing edge deployment of Kestrel server or HTTP.sys server. Only one HTTPS port is used by the app. The middleware discovers the port via IServerAddressesFeature.
Note
When an app is run in a reverse proxy configuration, IServerAddressesFeature isn't available. Set the port using one of the other approaches described in this section.
Edge deployments
When Kestrel or HTTP.sys is used as a public-facing edge server, Kestrel or HTTP.sys must be configured to listen on both:
- The secure port where the client is redirected (typically, 443 in production and 5001 in development).
- The insecure port (typically, 80 in production and 5000 in development).
The insecure port must be accessible by the client in order for the app to receive an insecure request and redirect the client to the secure port.
For more information, see Kestrel endpoint configuration or HTTP.sys web server implementation in ASP.NET Core.
Deployment scenarios
Any firewall between the client and server must also have communication ports open for traffic.
If requests are forwarded in a reverse proxy configuration, use Forwarded Headers Middleware before calling HTTPS Redirection Middleware. Forwarded Headers Middleware updates the Request.Scheme, using the X-Forwarded-Proto header. The middleware permits redirect URIs and other security policies to work correctly. When Forwarded Headers Middleware isn't used, the backend app might not receive the correct scheme and end up in a redirect loop. A common end user error message is that too many redirects have occurred.
When deploying to Azure App Service, follow the guidance in Tutorial: Bind an existing custom SSL certificate to Azure Web Apps.
Options
Macos Determine App Using Port Number
The following highlighted code calls AddHttpsRedirection to configure middleware options:
Calling AddHttpsRedirection is only necessary to change the values of HttpsPort or RedirectStatusCode.
The preceding highlighted code:
- Sets HttpsRedirectionOptions.RedirectStatusCode to Status307TemporaryRedirect, which is the default value. Use the fields of the StatusCodes class for assignments to
RedirectStatusCode. - Sets the HTTPS port to 5001.
Configure permanent redirects in production
Macos Determine App Using Portal
The middleware defaults to sending a Status307TemporaryRedirect with all redirects. If you prefer to send a permanent redirect status code when the app is in a non-Development environment, wrap the middleware options configuration in a conditional check for a non-Development environment.
Macos Ports In Use
When configuring services in Startup.cs:
HTTPS Redirection Middleware alternative approach
An alternative to using HTTPS Redirection Middleware (UseHttpsRedirection) is to use URL Rewriting Middleware (AddRedirectToHttps). AddRedirectToHttps can also set the status code and port when the redirect is executed. For more information, see URL Rewriting Middleware.
When redirecting to HTTPS without the requirement for additional redirect rules, we recommend using HTTPS Redirection Middleware (UseHttpsRedirection) described in this topic.
HTTP Strict Transport Security Protocol (HSTS)
Per OWASP, HTTP Strict Transport Security (HSTS) is an opt-in security enhancement that's specified by a web app through the use of a response header. When a browser that supports HSTS receives this header:
- The browser stores configuration for the domain that prevents sending any communication over HTTP. The browser forces all communication over HTTPS.
- The browser prevents the user from using untrusted or invalid certificates. The browser disables prompts that allow a user to temporarily trust such a certificate.
Because HSTS is enforced by the client, it has some limitations:
- The client must support HSTS.
- HSTS requires at least one successful HTTPS request to establish the HSTS policy.
- The application must check every HTTP request and redirect or reject the HTTP request.
ASP.NET Core 2.1 and later implements HSTS with the UseHsts extension method. The following code calls UseHsts when the app isn't in development mode:
UseHsts isn't recommended in development because the HSTS settings are highly cacheable by browsers. By default, UseHsts excludes the local loopback address.
For production environments that are implementing HTTPS for the first time, set the initial HstsOptions.MaxAge to a small value using one of the TimeSpan methods. Set the value from hours to no more than a single day in case you need to revert the HTTPS infrastructure to HTTP. After you're confident in the sustainability of the HTTPS configuration, increase the HSTS max-age value; a commonly used value is one year.
The following code:
- Sets the preload parameter of the
Strict-Transport-Securityheader. Preload isn't part of the RFC HSTS specification, but is supported by web browsers to preload HSTS sites on fresh install. For more information, see https://hstspreload.org/. - Enables includeSubDomain, which applies the HSTS policy to Host subdomains.
- Explicitly sets the
max-ageparameter of theStrict-Transport-Securityheader to 60 days. If not set, defaults to 30 days. For more information, see the max-age directive. - Adds
example.comto the list of hosts to exclude.
UseHsts excludes the following loopback hosts:
localhost: The IPv4 loopback address.127.0.0.1: The IPv4 loopback address.[::1]: The IPv6 loopback address.
Opt-out of HTTPS/HSTS on project creation
In some backend service scenarios where connection security is handled at the public-facing edge of the network, configuring connection security at each node isn't required. Web apps that are generated from the templates in Visual Studio or from the dotnet new command enable HTTPS redirection and HSTS. For deployments that don't require these scenarios, you can opt-out of HTTPS/HSTS when the app is created from the template.
To opt-out of HTTPS/HSTS:
Uncheck the Configure for HTTPS check box.
Use the --no-https option. For example
Trust the ASP.NET Core HTTPS development certificate on Windows and macOS
The .NET Core SDK includes an HTTPS development certificate. The certificate is installed as part of the first-run experience. For example, dotnet --info produces a variation of the following output:
Installing the .NET Core SDK installs the ASP.NET Core HTTPS development certificate to the local user certificate store. The certificate has been installed, but it's not trusted. To trust the certificate, perform the one-time step to run the dotnet dev-certs tool:
The following command provides help on the dev-certs tool:
How to set up a developer certificate for Docker
See this GitHub issue.
Trust HTTPS certificate from Windows Subsystem for Linux
The Windows Subsystem for Linux (WSL) generates an HTTPS self-signed cert. To configure the Windows certificate store to trust the WSL certificate:
Run the following command to export the WSL-generated certificate:
In a WSL window, run the following command:
The preceding command sets the environment variables so Linux uses the Windows trusted certificate.
Troubleshoot certificate problems
This section provides help when the ASP.NET Core HTTPS development certificate has been installed and trusted, but you still have browser warnings that the certificate is not trusted. The ASP.NET Core HTTPS development certificate is used by Kestrel.
All platforms - certificate not trusted
Run the following commands:
Close any browser instances open. Open a new browser window to app. Certificate trust is cached by browsers.
The preceding commands solve most browser trust issues. If the browser is still not trusting the certificate, follow the platform-specific suggestions that follow.
Docker - certificate not trusted
- Delete the C:Users{USER}AppDataRoamingASP.NETHttps folder.
- Clean the solution. Delete the bin and obj folders.
- Restart the development tool. For example, Visual Studio, Visual Studio Code, or Visual Studio for Mac.
Windows - certificate not trusted
- Check the certificates in the certificate store. There should be a
localhostcertificate with theASP.NET Core HTTPS development certificatefriendly name both underCurrent User > Personal > CertificatesandCurrent User > Trusted root certification authorities > Certificates - Remove all the found certificates from both Personal and Trusted root certification authorities. Do not remove the IIS Express localhost certificate.
- Run the following commands:
Close any browser instances open. Open a new browser window to app.
OS X - certificate not trusted
- Open KeyChain Access.
- Select the System keychain.
- Check for the presence of a localhost certificate.
- Check that it contains a
+symbol on the icon to indicate it's trusted for all users. - Remove the certificate from the system keychain.
- Run the following commands:
Close any browser instances open. Open a new browser window to app.
See HTTPS Error using IIS Express (dotnet/AspNetCore #16892) for troubleshooting certificate issues with Visual Studio.
IIS Express SSL certificate used with Visual Studio
To fix problems with the IIS Express certificate, select Repair from the Visual Studio installer. For more information, see this GitHub issue.
Additional information
localhost: The IPv4 loopback address.127.0.0.1: The IPv4 loopback address.[::1]: The IPv6 loopback address.
Opt-out of HTTPS/HSTS on project creation
In some backend service scenarios where connection security is handled at the public-facing edge of the network, configuring connection security at each node isn't required. Web apps that are generated from the templates in Visual Studio or from the dotnet new command enable HTTPS redirection and HSTS. For deployments that don't require these scenarios, you can opt-out of HTTPS/HSTS when the app is created from the template.
To opt-out of HTTPS/HSTS:
Uncheck the Configure for HTTPS check box.
Use the --no-https option. For example
Trust the ASP.NET Core HTTPS development certificate on Windows and macOS
The .NET Core SDK includes an HTTPS development certificate. The certificate is installed as part of the first-run experience. For example, dotnet --info produces a variation of the following output:
Installing the .NET Core SDK installs the ASP.NET Core HTTPS development certificate to the local user certificate store. The certificate has been installed, but it's not trusted. To trust the certificate, perform the one-time step to run the dotnet dev-certs tool:
The following command provides help on the dev-certs tool:
How to set up a developer certificate for Docker
See this GitHub issue.
Trust HTTPS certificate from Windows Subsystem for Linux
The Windows Subsystem for Linux (WSL) generates an HTTPS self-signed cert. To configure the Windows certificate store to trust the WSL certificate:
Run the following command to export the WSL-generated certificate:
In a WSL window, run the following command:
The preceding command sets the environment variables so Linux uses the Windows trusted certificate.
Troubleshoot certificate problems
This section provides help when the ASP.NET Core HTTPS development certificate has been installed and trusted, but you still have browser warnings that the certificate is not trusted. The ASP.NET Core HTTPS development certificate is used by Kestrel.
All platforms - certificate not trusted
Run the following commands:
Close any browser instances open. Open a new browser window to app. Certificate trust is cached by browsers.
The preceding commands solve most browser trust issues. If the browser is still not trusting the certificate, follow the platform-specific suggestions that follow.
Docker - certificate not trusted
- Delete the C:Users{USER}AppDataRoamingASP.NETHttps folder.
- Clean the solution. Delete the bin and obj folders.
- Restart the development tool. For example, Visual Studio, Visual Studio Code, or Visual Studio for Mac.
Windows - certificate not trusted
- Check the certificates in the certificate store. There should be a
localhostcertificate with theASP.NET Core HTTPS development certificatefriendly name both underCurrent User > Personal > CertificatesandCurrent User > Trusted root certification authorities > Certificates - Remove all the found certificates from both Personal and Trusted root certification authorities. Do not remove the IIS Express localhost certificate.
- Run the following commands:
Close any browser instances open. Open a new browser window to app.
OS X - certificate not trusted
- Open KeyChain Access.
- Select the System keychain.
- Check for the presence of a localhost certificate.
- Check that it contains a
+symbol on the icon to indicate it's trusted for all users. - Remove the certificate from the system keychain.
- Run the following commands:
Close any browser instances open. Open a new browser window to app.
See HTTPS Error using IIS Express (dotnet/AspNetCore #16892) for troubleshooting certificate issues with Visual Studio.
IIS Express SSL certificate used with Visual Studio
To fix problems with the IIS Express certificate, select Repair from the Visual Studio installer. For more information, see this GitHub issue.
Additional information
How do I determine if a port is in use under Linux or Unix-like system? How can I verify which ports are listening on Linux server? How do I check if port is in use on Linux operating system using the CLI?It is important you verify which ports are listening on the server's network interfaces. You need to pay attention to open ports to detect an intrusion. Apart from an intrusion, for troubleshooting purposes, it may be necessary to check if a port is already in use by a different application on your servers. For example, you may install Apache and Nginx server on the same system. So it is necessary to know if Apache or Nginx is using TCP port # 80/443. This quick tutorial provides steps to use the netstat, nmap and lsof command to check the ports in use and view the application that is utilizing the port.
How to check if port is in use in
To check the listening ports and applications on Linux:
- Open a terminal application i.e. shell prompt.
- Run any one of the following command on Linux to see open ports:
sudo lsof -i -P -n | grep LISTEN
sudo netstat -tulpn | grep LISTEN
sudo lsof -i:22 ## see a specific port such as 22 ##
sudo nmap -sTU -O IP-address-Here - For the latest version of Linux use the ss command. For example, ss -tulw
Let us see commands and its output in details.
Option #1: lsof command
The syntax is:$ sudo lsof -i -P -n
$ sudo lsof -i -P -n | grep LISTEN
$ doas lsof -i -P -n | grep LISTEN ### [OpenBSD] ###
Sample outputs:
Consider the last line from above outputs:
- sshd is the name of the application.
- 10.86.128.138 is the IP address to which sshd application bind to (LISTEN)
- 22 is the TCP port that is being used (LISTEN)
- 85379 is the process ID of the sshd process
Option #2: netstat command
You can check the listening ports and applications with netstat as follows.
Linux netstat syntax
Run netstat command along with grep command to filter out port in LISTEN state:$ netstat -tulpn | grep LISTEN
The netstat command deprecated for some time on Linux. Therefore, you need to use the ss command as follows:sudo ss -tulw
sudo ss -tulwn
Where ss command options are as follows:
- -t : Show only TCP sockets on Linux
- -u : Display only UDP sockets on Linux
- -l : Show listening sockets. For example, TCP port 22 is opened by SSHD server.
- -p : List process name that opened sockets
- -n : Don't resolve service names i.e. don't use DNS
Related: Linux Find Out Which Process Is Listening Upon a Port
FreeBSD/MacOS X netstat syntax
$ netstat -anp tcp | grep LISTEN
$ netstat -anp udp | grep LISTEN
OpenBSD netstat syntax
$ netstat -na -f inet | grep LISTEN
$ netstat -nat | grep LISTEN
Option #3: nmap command
The syntax is:$ sudo nmap -sT -O localhost
$ sudo nmap -sU -O 192.168.2.13 ##[ list open UDP ports ]##
$ sudo nmap -sT -O 192.168.2.13 ##[ list open TCP ports ]##
Sample outputs:
You can combine TCP/UDP scan in a single command:$ sudo nmap -sTU -O 192.168.2.13
A note about Windows users
You can check port usage from Windows operating system using following command: netstat -bano | more
netstat -bano | grep LISTENING
netstat -bano | findstr /R /C:'[LISTEING]'
Conclusion
This page explained command to determining if a port is in use on Linux or Unix-like server. For more information see the nmap command and lsof command page online here
