Linux

intro Resource isolation is an hot topic these days, and it’s a problem excellently solved by containerization. However, we can achieve isolation between internal tasks of an operating system by leveraging a technology exposed by the kernel: cgroups. This component is also used by Docker, and other Linux container technologies. Cgroups are the Linux way of organizing groups of processes: roughly speaking a cgroup is to a process what a process is to a thread: one can have many threads belonging to the same process, and in the same way one can join many processes inside the same cgroup. ...

I like playing with the D programming language and I wrote this little post to show how it’s easy to create a dynamic library (shared object, .so) that can be invoked in other programs; to have a little fun we will write a D replacement for the rand() C standard library function call. For your convenience, all the code is also on github Let’s start with the demo implementation, a C program that calls 10 times the stdlib function rand() to get a random number. ...

I am quite a fan of the D programming language and I think it deserves more attention, even if since a few months it’s becoming more and more popular, as it gained top20 in the TIOBE Index for February 2020. As an experiment in network programming, I took this simple NTP client written in C and translated to D ; in my opinion while it’s keeping the low-level nature, it’s shorter, clearer and more effective. It’s only a dozen lines of code, but full program is available on my github; stars and contributions are welcome! ...

As you may know, you can configure any DHCP server to send many options to the clients; for example to setup dns domains, http proxy (WPAD) and so on. If you need to access these options from a linux client, you must configure the client to ASK the server for the new options, by editing /etc/dhcp/dhclient.conf, and add an entry like: option WPAD code 252 = string; also request WPAD; done that, when you’ll ask for a dhcp, the dhclient process will invoke your hook scripts with two new environment variables, old_WPAD and new_WPAD, with the values before and after the renewal. ...