SecurityManager in Java is to check whether the application codes can access some restricted resource such as file, socket etc. This can be used in applications which have high security requirements. With this feature turned on, our system resources can be secured with only permitted operations.When JVM starts, it will first check whether the SecurityManager is on by checking the system property java.security.manager, if it's on, then an instance of SecurityManager will be created and it can be used to check different permissions. By default the security manager is off, but there are a few way...

In our day to day work. We may have many chances working on Linux/Unix systems. There are many things we may need to do, checking logs, navigating in directories, creating file or installing software. We may use many commands to complete the work, such as ls, mkdir, cd etc.Below are my frequently used Linux commands or programs recently:pwd : print working directory, sometimes I need to check which working directory I am in in order to know where to go next.ls : List current directory files, before I can operate on a directory, I need to know what are in the directory so that I may not delete ...