Sending data in a signal

The well-known kill system call has been around for decades and is used to send a signal to another process. The most common use is to terminate or kill another process by sending the KILL or TERM signal but it can be used for a form of IPC, usually around giving the other process a “kick” to do something.

One thing that isn’t as well known is besides sending a signal to a process, you can send some data to it. This can either be an integer or a pointer and uses similar semantics to the known kill and signal handler. I came across this when there was a merge request for procps. The main changes are using sigqueue instead of kill in the sender and using a signal action not a signal handler in the receiver.

WordPress 5.4

Debian packages for WordPress version 5.4 will be uploaded shortly. I’m just going through the install testing now. One problem I have noticed is, at least for my setup, there is an issue with network updates. The problem is that WordPress will ask me if I want to update the network sites, I say yes