SuperSluether disturbed my sleep to write:
Hi,
My Raspberry Pi and Ubuntu Server already have the updated version of libc6. Is a reboot still required? I thought only kernel updates required a reboot.
When you update a shared library, any running program that uses that library still has the *old* copy in memory until that program is restarted. Say you've got a program named "foo" running on your server that uses a library named "libbar", and you upgrade libbar without restarting foo. The running instance of foo still has the *old* version of libbar in its memory, and will not get the new one until it's restarted.
Most libraries aren't so central to everything that runs in Linux, and restarting the programs that use the library in question is a perfectly fine way to ensure you get the new library loaded. But libc is so very central to absolutely *everything* (or nearly so) in Linux that the best way to ensure everything gets the new, patched versions is simply to reboot.