There is a package in Debian (and no doubt also in its derivatives) called “usrmerge” <https://wiki.debian.org/UsrMerge>. The mere act of installing this will perform a “usr merge” on your system, which means that the contents of /bin are merged with /usr/bin, with the former becoming just a symlink to the latter, and similarly /sbin merged into /usr/sbin, and /lib merged into /usr/lib. Back in the last century, when hard drives were smaller, it was standard practice to put only the minimum core of executables and libraries into /bin, /sbin and /lib that would allow the system to boot into a state where a sysadmin could perform some basic maintenance tasks. All the less crucial, but nice to have stuff, would be in /usr, which would be mounted as a separate disk or partition. This way, I suppose, problems with the /usr volume could be fixed without the entire system becoming unbootable. These days, such a division is considered an anachronism. Debian hasn’t supported booting without /usr available for a long while now. I think some other distros, like Fedora, made the move a long time ago. And if you have problems with your OS partition, it’s easier to boot and fix things with something like SystemRescueCD anyway. Note that the usr merge, once performed, is not (easily) reversible. Also note that new Debian installs have been creating a merged usr system since version 10.