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<!-- The actual name of your proposed change page should look something like: Changes/Your_Change_Proposal_Name.  This keeps all change proposals in the same namespace -->
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= Remove and deprecate ''nscd'' in favour of ''sssd'' and ''systemd-resolved'' <!-- The name of your change proposal --> =
= Remove ''nscd'' <!-- The name of your change proposal --> =


== Summary ==
== Summary ==
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Note that motivation for the change should be in the Benefit to Fedora section below, and this part should answer the question "What?" rather than "Why?". -->
Note that motivation for the change should be in the Benefit to Fedora section below, and this part should answer the question "What?" rather than "Why?". -->


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.
This proposal intends to remove the ''nscd'' cache for named services in Fedora 35. nscd is already [[Changes/DeprecateNSCD|planned for deprecation]] in Fedora 34. The functionality it currently provides can be achieved by using ''systemd-resolved'' for DNS caching and the ''sssd'' daemon for everything else.


== Owner ==
== Owner ==
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== Current status ==
== Current status ==
[[Category:ChangePageIncomplete]]
[[Category:ChangeAcceptedF36]]
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[[Category:SelfContainedChange]]
[[Category:SystemWideChange]]
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* Targeted release: [[Releases/34 | Fedora 34 ]]  
* Targeted release: [[Releases/36 | Fedora 36 ]]  
* Last updated: <!-- this is an automatic macro — you don't need to change this line -->  {{REVISIONYEAR}}-{{REVISIONMONTH}}-{{REVISIONDAY2}}  
* Last updated: <!-- this is an automatic macro — you don't need to change this line -->  {{REVISIONYEAR}}-{{REVISIONMONTH}}-{{REVISIONDAY2}}  
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CLOSED as NEXTRELEASE -> change is completed and verified and will be delivered in next release under development
CLOSED as NEXTRELEASE -> change is completed and verified and will be delivered in next release under development
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* FESCo issue: <will be assigned by the Wrangler>
* FESCo issue: [https://pagure.io/fesco/issue/2501 #2501]
* Tracker bug: <will be assigned by the Wrangler>
* Tracker bug: [https://bugzilla.redhat.com/show_bug.cgi?id=1905142 #1905142]
* Release notes tracker: <will be assigned by the Wrangler>
* Release notes tracker: [https://pagure.io/fedora-docs/release-notes/issue/610 #610]


== Detailed Description ==
== 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.
''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 remove ''nscd'' in Fedora 35 and replace it with functionality provided by ''systemd-resolved'' for the `hosts` database and the ''sssd'' daemon for everything else. Accordingly, the `nscd` sub-package of glibc will be removed in Fedora 35 after being deprecated in Fedora 34.


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== Benefit to Fedora ==
== 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 [[Changes/systemd-resolved | Fedora 33 onwards]].
The benefits of this change are [[Changes/DeprecateNSCD#Benefit_to_Fedora|already described]] in the deprecation change proposal.
 
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.


<!-- What is the benefit to the distribution?  Will the software we generate be improved? How will the process of creating Fedora releases be improved?
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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.
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 for caching other than DNS in an earlier release of Fedora will need to install and configure sssd instead in order to re-enable caching. For caching DNS queries, Fedora already has systemd-resolved enabled by [[Changes/systemd-resolved|default since Fedora 33]].


* Other developers:
* Other developers:
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`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.
`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.
`systemd` supports flushing of the nscd cache when users are added or removed. This support will be dropped at compilation time ([https://github.com/systemd/systemd/pull/17879 upstream pull request]).


* Release engineering:
* Release engineering:
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<!-- Does your proposal align with the current Fedora Objectives: https://docs.fedoraproject.org/en-US/project/objectives/ ? It's okay if it doesn't, but it's something to consider -->
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Yes, this proposal aligns with the [https://docs.fedoraproject.org/en-US/project/objectives current objective] of "Fedora Minimization".
While this proposal does not directly move any of the currently stated [https://docs.fedoraproject.org/en-US/project/objectives objectives] forward, it is not opposed to any.


== Upgrade/compatibility impact ==
== Upgrade/compatibility impact ==
<!-- What happens to systems that have had a previous versions of Fedora installed and are updated to the version containing this change? Will anything require manual configuration or data migration? Will any existing functionality be no longer supported? -->
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The nscd sub-package depends on a glibc version that is identical to itself. This means that updating from a previous version of Fedora with nscd installed on it to Fedora 34 (which will not ship nscd) will require nscd to be removed first so that glibc can be updated.
The nscd sub-package depends on a glibc version that is identical to itself. This means that once it is removed and marked as obsolete in Fedora 35, updating from a previous release of Fedora with nscd installed on it, the old nscd package will be uninstalled during the update. Named services caching will cease to function, but the only effect will be slower resolution due to the missing cache. This will be more marked in systems that use remote remote authentication services like LDAP. Functionality will not be affected in any way.


The hosts cache will automatically be replaced by the one provided by systemd-resolved. However, in order to restore caching functionality for other caches provided by nscd, user will need to install and/or configure sssd (by enabling sssd with authconfig, and editing `/etc/sssd/sssd.conf` to enable it to work with nss).
The hosts cache will automatically be replaced by the one provided by systemd-resolved. However, in order to restore caching functionality for other caches provided by nscd, the system administrator will need to install and/or configure sssd (by enabling sssd with authconfig, and editing `/etc/sssd/sssd.conf` to enable it to work with nss).


== How To Test ==
== How To Test ==
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  - Green has been scientifically proven to be the most relaxing color. The move to a default background color of green with green text will result in Fedora users being the most relaxed users of any operating system.
  - Green has been scientifically proven to be the most relaxing color. The move to a default background color of green with green text will result in Fedora users being the most relaxed users of any operating system.
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* Most users will be unaffected by this change because nscd is not installed by default. It is usually used on systems configured with LDAP, where nscd provides caching of remote queries.
* On a system using nscd that is updated to Fedora 35 from a previous version, the system administrator will need to install and configure sssd to replace it after the update. Even when this is not done, the only visible affect will be slower resolution of named service queries due to a missing cache.
* Users on a system running sssd and systemd-resolved instead of nscd shouldn't see any noticeable difference in system behaviour or latency in resolving named services.


== Dependencies ==
== Dependencies ==
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<!-- If you cannot complete your feature by the final development freeze, what is the backup plan?  This might be as simple as "Revert the shipped configuration".  Or it might not (e.g. rebuilding a number of dependent packages).  If you feature is not completed in time we want to assure others that other parts of Fedora will not be in jeopardy.  -->
* Contingency mechanism: Revert changes to glibc spec file and continue to ship nscd. Revert changes to libuser and nss-pam-ldapd packages; this will need to be done by the respective package maintainers.
* Contingency mechanism: Revert changes to `glibc` spec file and continue to ship nscd. Revert changes to `libuser`, `nss-pam-ldapd`, and `systemd` packages; this will need to be done by the respective package maintainers.


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* Contingency deadline: Fedora 34 Beta Freeze
* Contingency deadline: Fedora 35 Beta Freeze
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* Blocks release? N/A (not a System Wide Change)
* Blocks release? N/A (not a System Wide Change)

Latest revision as of 13:43, 21 April 2022


Remove nscd

Summary

This proposal intends to remove the nscd cache for named services in Fedora 35. nscd is already planned for deprecation in Fedora 34. The functionality it currently provides can be achieved by using systemd-resolved for DNS caching and the sssd daemon for everything else.

Owner

Current status

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 remove nscd in Fedora 35 and replace it with functionality provided by systemd-resolved for the hosts database and the sssd daemon for everything else. Accordingly, the nscd sub-package of glibc will be removed in Fedora 35 after being deprecated in Fedora 34.


Benefit to Fedora

The benefits of this change are already described in the deprecation change proposal.


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 for caching other than DNS in an earlier release of Fedora will need to install and configure sssd instead in order to re-enable caching. For caching DNS queries, Fedora already has systemd-resolved enabled by default since Fedora 33.

  • 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.

systemd supports flushing of the nscd cache when users are added or removed. This support will be dropped at compilation time (upstream pull request).

  • Release engineering:

This change does not require coordination with or have impact on release engineering and does not require a mass rebuild.

  • Policies and guidelines: N/A (not a System Wide Change)
  • Trademark approval: N/A (not needed for this Change)
  • Alignment with Objectives:

While this proposal does not directly move any of the currently stated objectives forward, it is not opposed to any.

Upgrade/compatibility impact

The nscd sub-package depends on a glibc version that is identical to itself. This means that once it is removed and marked as obsolete in Fedora 35, updating from a previous release of Fedora with nscd installed on it, the old nscd package will be uninstalled during the update. Named services caching will cease to function, but the only effect will be slower resolution due to the missing cache. This will be more marked in systems that use remote remote authentication services like LDAP. Functionality will not be affected in any way.

The hosts cache will automatically be replaced by the one provided by systemd-resolved. However, in order to restore caching functionality for other caches provided by nscd, the system administrator will need to install and/or configure sssd (by enabling sssd with authconfig, and editing /etc/sssd/sssd.conf to enable it to work with nss).

How To Test

N/A (not a System Wide Change)

User Experience

  • Most users will be unaffected by this change because nscd is not installed by default. It is usually used on systems configured with LDAP, where nscd provides caching of remote queries.
  • On a system using nscd that is updated to Fedora 35 from a previous version, the system administrator will need to install and configure sssd to replace it after the update. Even when this is not done, the only visible affect will be slower resolution of named service queries due to a missing cache.
  • Users on a system running sssd and systemd-resolved instead of nscd shouldn't see any noticeable difference in system behaviour or latency in resolving named services.

Dependencies

  • 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.

Both changes are minimal, requiring a removal of the dependency in the spec file, and a rebuild.

Contingency Plan

  • Contingency mechanism: Revert changes to glibc spec file and continue to ship nscd. Revert changes to libuser, nss-pam-ldapd, and systemd packages; this will need to be done by the respective package maintainers.
  • Contingency deadline: Fedora 35 Beta Freeze
  • Blocks release? N/A (not a System Wide Change)
  • Blocks product? None

Documentation

N/A (not a System Wide Change)

Release Notes