Shell script is frequently used when monitoring system status on Linux. It's not an easy task to write shell script but it's a very important skill for developers and system administrators to ease work and automate common tasks. This post will share some common interview questions about shell script.1. Get random characters(8 characters)Method 1# echo $RANDOM |md5sum |cut -c 1-8471b94f2Method 2# openssl rand -base64 4vg3BEg==Method 3# cat /proc/sys/kernel/random/uuid |cut -c 1-8ed9e032c2. Get random numbers(8 digits)Method 1# echo $RANDOM |cksum |cut -c 1-823648321Method 2# openssl rand -...

Lots of you may have encountered some error message stating that the port has been taken by another program while trying to start a program on Linux. And you would want to know which program takes the port you want to use. This post will provide some feasible ways to check out which program is taking a specific port.lsof -i:[port]lsof is the command to list open files on Linux. And if you know more about Linux you should get to know everything on Linux is a file even including network connection. Hence you can use lsof to list the network programs which are running.The -i option will...

Have you ever wondered how to take screen recording easily on Windows? Normally you would think to download some software online and install it on your machine such as Camtasia. However, many of them are either non-free or uneasy to use.Fortunately, there is a built-in tool provided in Windows 10 which can be used to take simple screen recording plus audio recording. The tool is called the Game Bar which is primarily intended for gamers to take screenshots of their plays and achievements. Don't be scared away by its name though, it is not only for game recording, it can also be used for taking...

As a system administrator or network engineer or application developer, there is a need to check whether a port on remote server is open so that you can tell whether the service under check is running or not. In this post, we would cover a few methods to check whether a remote server port is open or not on Linux.telnettelnet is the most frequently used command on both Windows and Linux to check port. The simple usage for this command is telnet [host] [port]When the port is open, the output will be like:Trying 192.168.56.160...Connected to 192.168.56.160.Escape character is '^]'.SSH-2.0-Op...

 As the Linux kernel has become one of the most gigantic and complex software project in the world, its complication scare many novices away. In this post, I will give some personal experience on how to learn Linux kernel, and hope these tips can offer some help to newcomers.(1) Download vanilla kernel and install it.Yes, I suggest you can find a physical machine, or if you really don’t have one at hand, virtual machine is also OK. Download the newest vanilla kernel from kernel.org, then build and install it. This process isn’t too hard and makes you c...

When a Linux server is running, it has to have an IP so that other machines can talk to it. It is often desired that the server would own a static IP so that every time other machines want to connect to it, the same IP address would be used. This is extremely useful when there are virtual machines installed on a host machine where the virtual machine would start and stop now and then. To configure static IP address for a Linux server, the /etc/network/interfaces needs to be updated. Assuming there is a host only network is created for a network interface named eth1. The configuration woul...

After login to a Linux system, the command console will show up with a prompt label such as # or ~, a shell command can be typed after this prompt and the system can execute the command thereafter. All these operations are handled by shell.Shell is a command language interpreter that executes commands read from the standard input device (keyboard) or from a file. There are different types of shells such as bash, ksh, csh etc. The most commonly used of them is bash and it's also the default one on most Linux distributions.There are two very important configuration files for bash : bas...

As a beginner user of Unix or Linux, people would frequently get confused about the use of different directories of the system. For example, there is a /bin directory under root(/), it is used to store binary files. However, there are /usr/bin and /usr/local/bin under /usr which are used for storing binary files as well. Some systems even have /opt/bin. What are the differences among them?Though there are articles explaining different directories in *nix such as Filesystem Hierarchy Standard, it's not clear why these directories are present and their history. Rob Landley filled part ...