Describe the mknod command and when you’d use it.

The mknod command creates device special files or fifos.

mknod was originally used to create the character and block devices that populate /dev/. Nowadays software like udev automatically creates and removes device nodes on the virtual filesystem when the corresponding hardware is detected by the kernel, but originally /dev was just a directory in / that was populated during install.

So yes, in case of a near complete disaster causing the /dev virtual filesystem not to load and/or udev failing spectacularly, using mknod to painstakingly repopulate at least a rudimentary device tree to get something back up can be done... But yeah, that's sysadmin horror story time. Personally, I recommend a rescue USB stick or CD.

Aside from creating named pipes, I can't think of a single possible day-to-day use for it that an end user would need to concern themselves with -- and even that is stretching the definition of 'day to day use'.

Source: https://unix.stackexchange.com/questions/10723/what-is-the-mknod-command-used-for