F40 Change Proposal: F40 Change Proposal: Unify /usr/bin and /usr/sbin (System-Wide)

[Aoife Moloney]

Wiki -> https://fedoraproject.org/wiki/Changes/Unify_bin_and_sbin

This document represents a proposed Change. As part of the Changes
process, proposals are publicly announced in order to receive
community feedback. This proposal will only be implemented if approved
by the Fedora Engineering Steering Committee.

== Summary ==
The `/usr/sbin` directory becomes a symlink to `bin`, which means
paths like `/usr/bin/foo` and `/usr/sbin/foo` point to the same place.
`/bin` and `/sbin` are already symlinks to `/usr/bin` and `/usr/sbin`,
so effectively `/bin/foo` and `/sbin/foo` also point to the same
place. `/usr/sbin` will be removed from the default `$PATH`.

== Owner ==
* Name: [[User:zbyszek|Zbigniew Jędrzejewski-Szmek]]
* Email: zbyszek at in.waw.pl



== Detailed Description ==
The split between `/bin` and `/sbin` is not useful, and also unused.
The original split was to have "important" binaries statically linked
in `/sbin` which could then be used for emergency and rescue
operations. Obviously, we don't do static linking anymore. Later, the
split was repurposed to isolate "important" binaries that would only
be used by the administrator. While this seems attractive in theory,
in practice it's very hard to categorize programs like this, and
normal users routinely invoke programs from `/sbin`. Most programs
that require root privileges for ''certain'' operations are also used
when operating without privileges. And even when privileges are
required, often those are acquired dynamically, e.g. using `polkit`.
Since many years, the default `$PATH` set for users includes both
directories. With the advent of systemd this has become more
systematic: systemd sets `$PATH` with both directories for all users
and services. So in general, all users and programs would find both
sets of binaries.

One additional use of the `/bin`—`/sbin` split is `consolehelper`. In
this approach, the user-facing program (`/bin/foo`) is a symlink to
`/bin/consolehelper`, which is a suid binary that elevates privileges
and calls the "real" `foo` (`/sbin/foo` or `/usr/libexec/foo`). Most
uses of consolehelper have been moved to polkit
(https://fedoraproject.org/wiki/Features/UsermodeMigration), but some
users remain (https://bugzilla.redhat.com/show_bug.cgi?id=502765). Use
of `/sbin` for the privileged program is incompatible with the
proposed merge; those packages will need to be adjusted to move the
binary that requires privileges under `/usr/lib` or `/usr/libexec`
(see Scope below).

Since generally all user sessions and services have both directories
in `$PATH`, this split actually isn't ''used'' for anything. Its main
effect is confusion when people need to use the absolute path and
guess the directory wrong. Other distributions put some binaries in
the other directory, so the absolute path is often not portable. Also,
it is very easy for a user to end up with `/sbin` before `/bin` in
`$PATH`, and for an administrator to end up with `/bin` before `/sbin`
in `$PATH`, causing confusion. If this feature is dropped, the system
became a little bit simpler, which is useful especially for new users,
who are not aware of the history of the split.

Many years ago we merged `/bin` and `/usr/bin`
(https://fedoraproject.org/wiki/Features/UsrMove). In some ways
''that'' split was similar: it had historical justification that went
away more than a decade prior, it was impossible to cleanly categorize
programs into the the categories so effectively both parts were needed
for boot, and even though it was making the system more complicated
for little gain, the split was being carried forward because it was
easier to do so than to remove it
(http://www.freedesktop.org/wiki/Software/systemd/TheCaseForTheUsrMerge).
''This'' split is much less visible, but it's also making the system
more complicated for no gain, and removing it is the natural
follow-up.

== Feedback ==


== Benefit to Fedora ==
* Packagers don't have to think whether to install programs in
`%_bindir` or `%_sbindir`.
* Users don't have to think whether programs are in `%_bindir` or `%_sbindir`.
* Fedora becomes more compatible with other distributions (for
example, we have `/sbin/ip` while Debian has `/bin/ip`, and we have
`/bin/chmem` and `/bin/isosize`, but Debian has `/sbin/chmem` and
`/sbin/isosize`, and we also have
`/sbin/{addpart,delpart,lnstat,nstat,partx,ping,rdma,resizepart,ss,udevadm,update-alternatives}`,
while Debian has those in under `/bin`, etc.)
* Fedora becomes more compatible with Arch, which did the merge a few years ago.
* `execvp` and related functions iterate over fewer directories. This
probably doesn't matter for speed, but is a nice simplification when
looking at logs or `strace` output.

== Scope ==
* Proposal owners:
<!--
** Implement `split-bin=auto` in systemd: in this mode, systemd will
check at runtime whether `/usr/sbin` is a symlink to `/usr/bin`, and
if yes, behave like with `split-bin=no`, and otherwise
`split-bin=yes`.
** Adjust systemd package to build with `-Dsplit-bin=auto`.
-->
** Adjust `%_sbindir` in `/usr/lib/rpm/macros` (part of `rpm`
package). Packages will be updated automatically during the mass
rebuild.
** Add a `%filetrigger` to `filesystem` package to create symlinks to
`../bin/foo` for every `foo` that is uninstalled from `/usr/sbin`.
** Add a `%posttrans` trigger to `filesystem` package to check that
`/usr/sbin` only contains symlinks and do `ln -fs bin /usr/sbin`.
(Those scriptlets make it easier to have a smooth transition. At all
times, the old paths will still work. After the transition is complete
we can drop the scriptlets and provide the `/usr/sbin` symlink in the
`filesystem` package.)
** Adjust systemd package to build with `-Dsplit-bin=no`.
* Other developers: programs which user consolehelper and install the
same name under both directories will need to be adjusted to use a
different directory. Some of those packages may be retired instead.
See list below.

* Packages using usermode with binaries in both directories:
** `anaconda-live`
** `beesu`
** `chkrootkit`
** `hddtemp`
** `mate-system-log`
** `setuptool`
** `subscription-manager`
** `system-switch-java`
** `xawtv`

* Release engineering: [https://pagure.io/releng/issues #Releng issue number]

* Policies and guidelines:
https://docs.fedoraproject.org/en-US/packaging-guidelines/#_effect_of_the...
will need to be adjusted (and most likely retitled ;))

* Trademark approval: N/A (not needed for this Change)


* Alignment with Community Initiatives: nope

== Upgrade/compatibility impact ==
The change should be mostly invisible for users. While the transition
is ongoing, both sets of paths should work and users should have both
directories in `$PATH`. Once the transition is finished, both sets of
paths should work, but users will only have `/usr/bin` in `$PATH`.

== How To Test ==


== User Experience ==


== Dependencies ==


== Contingency Plan ==
* If the move of a binary of any specific package causes problems, we
can create a compat symlink like `/usr/sbin/foo → ../bin/foo` using a
`%postin` scriptlet in that package.
* If the change is causing problems in general and needs to be
reverted, we'd need to undo the changes to macro definitions in `rpm`
and rebuild some or all packages.
* Contingency deadline: in principle can be done at any time, but
would require a rebuild of some or all affected packages.
* Blocks release? no. It is OK if the change is done partially.

== Documentation ==

TBD.

== Release Notes ==



-- 
Aoife Moloney

Fedora Operations Architect

Fedora Project

Matrix: @amoloney:fedora.im

IRC: amoloney