How to install certbot on CentOS8

Written by Zhong Wei

The biggest problem you faced is actually the following one
https://otodiginet.com/operating-system/how-to-install-snapd-on-centos-8/

and the article above answers the question very well.

certbot certos

.NET Core: Set the correct CurrentCulture basing the `lang` header

Written by Zhong Wei

  1. Create a middleware to do that task

     public static void SetCurrentCulture(this IApplicationBuilder app)
 {
     app.Use(async (context, next) =>
     {
         var cultureQuery = context.Request.Headers["lang"] == "en" ? "en-US" : "zh-CN";
         if (!string.IsNullOrWhiteSpace(cultureQuery))
         {
             var culture = new CultureInfo(cultureQuery);
             CultureInfo.CurrentCulture = culture;
             CultureInfo.CurrentUICulture = culture;
         }
         await next();
     });
 }

  2. Use the middleware in Startup.cs

     public void Configure(IApplicationBuilder app, IWebHostEnvironment env, ILog logger,
     IExceptionEntityService exceptionEntityService)
 {
     ...
     app.SetCurrentCulture();
     ...
 }

Note: recover from accidentally changed the ownership of `sudo` command

Written by Zhong Wei

Cause:

This morning, I change to the /backup directory and found I cannot write in it. So I rapidly typed sudo chown -R david:david .. then press Enter. You know what happened! All the files in / directory were changing the owner to me! I realized this by seeing an error message like "You cannot change the owner of xxx file to david".

Damn, how silly I was! Unfortunately, that was not the end of my bad luck. When I try to revert it by typing sudo chown -R root:root /, I got another error message: /usr/bin/sudo must be owned by uid 0 and have the setuid bit set. Then I tried su - root but it seems that I haven't set a root password.

How can I recover my pop! OS?

  1. reboot it into single-user mode, edit the boot menu, add systemd.unit=rescue.target at the end of the boot line.
  2. In the boot console, chown -R root:root /usr; chmod 4755 /usr/bin/sudo; reboot

Rather easy, right? It did cost me over 10mins!

Linux is also fragile, please don't be such silly next time. I told myself. PS: This time I also set a root password as well, so next time I could run su - root directly instead of going to the single user mode.

什么是AOP？这种在运行时，动态地将代码切入到类的指定方法、指定位置上的编程思想就是面向切面的编程。

Written by Zhong Wei

什么是AOP？这种在运行时，动态地将代码切入到类的指定方法、指定位置上的编程思想就是面向切面的编程。

https://www.zhihu.com/question/24863332

Fix the ‘Too Many Open Files’ Error in a systemd service in Linux

Written by Zhong Wei

In short:

Change the service file, and add two lines after [Service] line, 

[Service]
LimitNOFILE=65535
LimitNOFILESoft=65535

If you want to know more, read the Reference