Changes/Unify bin and sbin

Unify /bin and /sbin

This is a proposed Change for Fedora Linux.
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/bar also point to the same place. /usr/sbin will be removed from the default $PATH.

Owner

• Name: Zbigniew Jędrzejewski-Szmek
• Email: zbyszek at in.waw.pl

Current status

• Targeted release: Fedora Linux 40
• Last updated: 2023-12-15
• [<will be assigned by the Wrangler> devel thread]
• FESCo issue: <will be assigned by the Wrangler>
• Tracker bug: <will be assigned by the Wrangler>
• Release notes tracker: <will be assigned by the Wrangler>

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 Things becomeincompatible 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.

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 setup package to create symlinks to ../bin/foo for every foo that is uninstalled from /usr/sbin.
  • Add a %posttrans trigger to setup package to check that /usr/sbin only contains symlinks and do ln -fs bin /usr/sbin.
• 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: #Releng issue number

• Policies and guidelines: https://docs.fedoraproject.org/en-US/packaging-guidelines/#_effect_of_the_usrmove_fedora_feature 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.

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.