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Unify /usr/bin and /usr/sbin

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. The same change is also done to make /usr/local/sbin point to bin, effectively making /usr/local/bin/foo and /usr/local/sbin/foo point to the same place. The definition of %_sbindir will be changed to %_bindir, so packages will start using the new directory after a rebuild without any further action. Maintainers may stop using %_sbindir, but don't need to.

Owner

Current status

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

https://lists.fedoraproject.org/archives/list/devel@lists.fedoraproject.org/message/TRQ3I7BDTHG6N7WQEQ7PMK3P6PVWXQMI/

"Programs in /usr/bin have their documentation in section 1 of the manual, while programs /usr/sbin are documented in section 8."

https://lists.fedoraproject.org/archives/list/devel@lists.fedoraproject.org/message/NALSOW35LXN6HZPULMQ46WXNGZO4SYK4/

"The manual sections have historical meaning:

https://en.wikipedia.org/wiki/Man_page#Manual_sections eg. 1 = general commands 8 = system administration

So unless the tools themselves are changing their purpose or are in the wrong section now, the manual sections should stay the same."

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:
    • Adjust %_sbindir in /usr/lib/rpm/macros (part of rpm package) to evaluate to %_bindir. 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.
    • File a pull request for Packaging Guidelines to stop mentioning %{_sbindir}. The macro will remain defined to avoid breakage of packages which use it.
  • Other developers:
    • Packages which install to hardcoded $DESTDIR/usr/sbin, but then use %{_sbindir} in %files, will need to be adjusted.
    • Packages which use 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
  • Packages which package a symlink in /usr/sbin that will need to be dropped:
    • opensmtpd
    • rpcbind
    • policycoreutils
    • systemd-udev
  • 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

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