Install Hadoop 2.8.2 on Centos
Assume all servers have been installed Centos 7 and all DNS records have been created on DNS Server.
Remove Known Host of Secure Shell on Chromebook
- Open Javascript console by CTRL + Shift + J
Mitigating DDoS Attacks with NGINX and NGINX Plus
Read MorePrevent MACBook Sleep
Some 3rd parties can prevent MacBook from sleep. Why does Apple always let MacBook/Air go to sleep when lid is closed and ignore user’s settings?
Fix Docker Exception - Credentials store error on MacOS
When I run docker-compose command on Mac OS, I hit an error as below:
docker.errors.DockerException: Credentials store error: StoreError('Credentials store docker-credential-osxkeychain exited with "User interaction is not allowed.".',)
Failed to execute script docker-compose
Nginx Proxy Server Configuration
Example 1:
server {
listen 80;
index index.html index.htm index.nginx-debian.html index.php;
server_name aaa.bbb.ccc.ddd;
location ~/app2(.*)$ {
proxy_set_header X-Real-IP $remote_addr;
proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
proxy_set_header Host $host;
proxy_pass http://aaa.bbb.ccc.ddd:8001$1;
}
}
Check Linux Listening Ports
ss comand
sudo ss -ltu
sudo ss -ltup #show process
Static Class vs Non-static Nested Class
Only nested classes (inner classes) can be static.
Override or Overload Static Methods in Java
Static methods can be overloaded but cannot be overrode.
Why String is immutable in Java
- String values are stored in String constant pool. It can be accessed by multiple client.
- It is used by the class loading mechanism. For security reason, it should not be changed to other value.
- Immutable string allow to cache its hashcode. It makes hashmap/hashtable very fast since they don’t calculate hashcode everytime.
- String instance is thread-safe in Java.