Changes/RemoveNSCD

Guidance
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Remove and deprecate nscd in favour of sssd and systemd-resolved

Summary

This proposal intends to replace the nscd cache for named services with systemd-resolved for the hosts database and the sssd daemon for everything else.

Owner

• Name: Arjun Shankar
• Email: arjun@redhat.com

Current status

• Targeted release: Fedora 34
• Last updated: 2020-10-09
• 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

nscd is a daemon that provides caching for accesses of the passwd, group, hosts, services, and netgroup databases through standard libc interfaces (such as getpwnam, getpwuid, getgrnam, getgrgid, gethostbyname, etc.). This proposal intends to replace nscd in Fedora with systemd-resolved for the hosts database and the sssd daemon for everything else. Accordingly, the nscd sub-package of glibc will be removed.

Benefit to Fedora

While still maintained within the glibc source tree, nscd has received less than forty commits in the past three years and has gathered significant technical debt, and has bugs which are hard to fix. There are concurrency bugs in the shared mappings, cache unification (IPv4 vs. IPv6 vs. AF_UNSPEC) issues, and more which would require significant investment to fix in nscd. Such an investment seems like duplicate effort among our communities given the quality and state of sssd, and systemd-resolved which is already proposed to be enabled by default from Fedora 33 onwards.

At a high level, sssd and systemd-resolved together provide a caching solution that has feature parity with nscd, with systemd-resolved covering the hosts cache and sssd the rest. The removal of nscd from Fedora will (a) move the user base over to a more modern solution for named services caching, and (b) reduce maintenance work on the Fedora glibc package and the duplication of effort on nscd upstream.

Scope

• Proposal owners:

The volume of work required is minimal, with the only change being the removal of the nscd sub-package offered by glibc which can be achieved by minor changes to the spec file. Since nscd is not installed by default, the affect on the distribution is minimal. Users who have installed nscd will need to install and configure sssd instead.

• Other developers:

nss-pam-ldapd has a weak dependency on nscd that will need to be removed. libuser has a build dependency on nscd that will also need to be removed.

• Release engineering: #Releng issue number (a check of an impact with Release Engineering is needed)

• Policies and guidelines: N/A (not a System Wide Change)

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

• Alignment with Objectives:

Yes, this proposal aligns with the current objective of "Fedora Minimization".

Upgrade/compatibility impact

N/A (not a System Wide Change)

How To Test

N/A (not a System Wide Change)

Dependencies

N/A (not a System Wide Change)

Contingency Plan

• Contingency mechanism: (What to do? Who will do it?) N/A (not a System Wide Change)
• Contingency deadline: N/A (not a System Wide Change)
• Blocks release? N/A (not a System Wide Change), Yes/No
• Blocks product? product

Documentation

N/A (not a System Wide Change)