Frequently Asked Question

What is the /usr merge and why are /bin and /usr/bin the same now?

For most of Linux's history, /bin, /sbin, and /lib lived on the root partition and held the bare minimum needed to boot to single-user mode; /usr/bin, /usr/sbin, and /usr/lib held everything else and could live on a separate partition mounted later. This split made sense in the 1970s when disks were tiny, Ken Thompson literally ran out of space and moved files onto a second disk, but on modern systems with an initramfs the root partition no longer needs to be self-sufficient, since the initramfs already mounts /usr before the system tries to use anything from it.

The /usr merge, championed by Fedora and now standard on Arch, openSUSE, recent Debian, and Ubuntu, replaces /bin, /sbin, /lib, and /lib64 with symlinks pointing into /usr. The benefits are real: /usr can be mounted read-only (or shared over the network, or snapshotted atomically), distribution packages don't have to worry about whether /bin/grep and /usr/bin/grep are the same file, and the layout matches Solaris and the systemd ecosystem's assumptions. Existing scripts using either path keep working because the symlinks resolve transparently.