## What is "merged `/usr`"
-"Merged `/usr`" describes a possible future standard directories scheme in which the `/{bin,sbin,lib}/` directories have been made superfluous, either through replacing them by symlinks to their `/usr` equivalents (/usr/{bin,sbin,lib}) or by removing them entirely.
+"Merged `/usr`" describes a possible future standard directories scheme in which the `/{bin,sbin,lib}/` directories have been made superfluous through replacing them by symlinks to their `/usr` equivalents (/usr/{bin,sbin,lib}).
The motivation to get Debian systems to converge towards such a scheme is vastly documented elsewhere ([FDO's TheCaseForTheUsrMerge][0], [wiki.d.o UsrMerge][1]) but can be summarized as the following points:
* having separate `/` and `/usr` filesystems has been useful in the past for booting without initramfs onto a minimal root filesystem that carried just enough to mount the `/usr` filesystem later in the boot process. Given the evolution of physical hosts' capabilities, initramfs'es have been default in Debian (and elsewhere) for a long time, and most systems no longer have an intermediate state during boot in which they have only `/`, but not `/usr`, mounted.
[0]: https://www.freedesktop.org/wiki/Software/systemd/TheCaseForTheUsrMerge/
[1]: https://wiki.debian.org/UsrMerge
+The compatibility symbolic links `/lib` → `/usr/lib` and `/lib64` → `/usr/lib64` are required by the various CPUs' platform ABIs (for example i386 requires `/lib/ld-linux.so.2` to resolve to glibc's `ld.so`, and amd64 requires `/lib64/ld-linux-x86-64.so.2`) so there are no plans to remove them altogether. Similarly, removing `/bin` is not under consideration because it would break the assumption that `/bin/sh` exists, and removing `/sbin` would break the assumption that `/sbin/fsck.*` and `/sbin/mount.*` exist.
+
## "merged `/usr`" in Debian
In Debian buster, the current testing suite, "merged `/usr`" is only considered for implementation with symlinks (there are no proposals for simply dropping `/{bin,sbin,lib}`) and is implemented in two distinct ways:
Various valid long-term desireable situations coexist, and while discussing immediate countermeasures, it is useful to keep the long-term outcome that those are most likely to produce.
-These are the five possible situations at the time of bullseye (buster + 1):
+These are the six possible situations at the time of bullseye (buster + 1):
-* `none`: "merged `/usr`" has been happened
+* `none`: "merged `/usr`" has been reverted
* `weak`: both directory schemes are allowed, packages only built on classical hosts
-* `hard`: both directory schemes are allowed, packages can be built anywhere
-* `all` : only "merged `/usr`" directory schemes are allowed, packages only built on "merged `/usr`" hosts
-* `full`: only "merged `/usr`" directory schemes are allowed, symlinks have been removed
+* `middle`: both directory schemes are allowed, packages can be built anywhere
+* `hard`: both directory schemes are allowed, packages only built on "merged `/usr`" hosts
+* `all`: only "merged `/usr`" directory schemes are allowed, packages only built on "merged `/usr`" hosts
It can be summarized by the following table:
+```
| | Host types that are allowed | Are merged-/usr | Official packages are built on | Packages built on … can break on the other |
| Codename | classical hosts | merged-/usr hosts | symlinks allowed | classical hosts | merged-/usr hosts | classical hosts | merged-/usr hosts |
|----------|-----------------|-------------------|------------------|—----------------|-------------------|---------------------|----------------------|
| none | yes | no | no | yes | no | yes | yes |
| weak | yes | yes | yes | yes | no | no | yes |
-| hard | yes | yes | yes | yes | yes | no | no |
+| middle | yes | yes | yes | yes | yes | no | no |
+| hard | yes | yes | yes | no | yes | no | no |
| all | no | yes | yes | no | yes | yes | no |
-| full | no | yes | no | no | yes | yes | yes |
+```
## Immediate actions
projects / debian-ctte.git / blobdiff