15137a29c2
* gnu/system/nss.scm (%mdns-host-lookup-nss): New variable. * doc/guix.texi (Name Service Switch): Document it.
237 lines
7.9 KiB
Scheme
237 lines
7.9 KiB
Scheme
;;; GNU Guix --- Functional package management for GNU
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;;; Copyright © 2015 Ludovic Courtès <ludo@gnu.org>
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;;;
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;;; This file is part of GNU Guix.
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;;;
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;;; GNU Guix is free software; you can redistribute it and/or modify it
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;;; under the terms of the GNU General Public License as published by
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;;; the Free Software Foundation; either version 3 of the License, or (at
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;;; your option) any later version.
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;;;
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;;; GNU Guix is distributed in the hope that it will be useful, but
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;;; WITHOUT ANY WARRANTY; without even the implied warranty of
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;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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;;; GNU General Public License for more details.
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;;;
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;;; You should have received a copy of the GNU General Public License
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;;; along with GNU Guix. If not, see <http://www.gnu.org/licenses/>.
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(define-module (gnu system nss)
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#:use-module (rnrs enums)
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#:use-module (guix records)
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#:use-module (srfi srfi-9)
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#:use-module (ice-9 match)
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#:export (name-service-switch?
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name-service-switch
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name-service?
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name-service
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lookup-specification
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%default-nss
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%mdns-host-lookup-nss
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%files
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%compat
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%dns
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name-service-switch->string))
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;;; Commentary:
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;;;
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;;; Bindings for libc's name service switch (NSS) configuration.
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;;;
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;;; Code:
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(define-record-type* <name-service> name-service
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make-name-service
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name-service?
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(name name-service-name)
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(reaction name-service-reaction
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(default (lookup-specification))))
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;; Lookup specification (info "(libc) Actions in the NSS Configuration").
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(define-enumeration lookup-action
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(return continue)
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make-lookup-action)
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(define-enumeration lookup-status
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(success
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not-found
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unavailable
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try-again)
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make-lookup-status)
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(define-record-type <lookup-status-negation>
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(lookup-status-negation status)
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lookup-status-negation?
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(status lookup-status-negation-status))
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(define-record-type <lookup-reaction>
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(make-lookup-reaction status action)
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lookup-reaction?
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(status lookup-reaction-status)
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(action lookup-reaction-action))
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(define-syntax lookup-reaction
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(syntax-rules (not =>)
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((_ ((not status) => action))
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(make-lookup-reaction (lookup-status-negation (lookup-status status))
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(lookup-action action)))
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((_ (status => action))
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(make-lookup-reaction (lookup-status status)
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(lookup-action action)))))
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(define-syntax-rule (lookup-specification reaction ...)
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"Return an NSS lookup specification."
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(list (lookup-reaction reaction) ...))
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;;;
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;;; Common name services and default NSS configuration.
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;;;
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(define %compat
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(name-service
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(name "compat")
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(reaction (lookup-specification (not-found => return)))))
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(define %files
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(name-service (name "files")))
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(define %dns
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;; DNS is supposed to be authoritative, so unless it's unavailable, return
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;; what it finds.
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(name-service
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(name "dns")
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(reaction (lookup-specification ((not unavailable) => return)))))
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;; The NSS. We list all the databases here because that allows us to
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;; statically ensure that the user's configuration refers to existing
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;; databases. See libc/nss/databases.def for the list of databases. Default
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;; values obtained by looking for "DEFAULT_CONFIG" in libc/nss/*.c.
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;;
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;; Although libc places 'dns' before 'files' in the default configurations of
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;; the 'hosts' and 'networks' databases, we choose to put 'files' before 'dns'
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;; by default, so that users can override host/address mappings in /etc/hosts
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;; and bypass DNS to improve their privacy and escape NSA's MORECOWBELL.
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(define-record-type* <name-service-switch> name-service-switch
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make-name-service-switch
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name-service-switch?
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(aliases name-service-switch-aliases
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(default '()))
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(ethers name-service-switch-ethers
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(default '()))
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(group name-service-switch-group
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(default (list %compat %files)))
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(gshadow name-service-switch-gshadow
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(default '()))
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(hosts name-service-switch-hosts
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(default (list %files %dns)))
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(initgroups name-service-switch-initgroups
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(default '()))
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(netgroup name-service-switch-netgroup
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(default '()))
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(networks name-service-switch-networks
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(default (list %files %dns)))
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(password name-service-switch-password
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(default (list %compat %files)))
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(public-key name-service-switch-public-key
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(default '()))
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(rpc name-service-switch-rpc
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(default '()))
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(services name-service-switch-services
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(default '()))
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(shadow name-service-switch-shadow
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(default (list %compat %files))))
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(define %default-nss
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;; Default NSS configuration.
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(name-service-switch))
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(define %mdns-host-lookup-nss
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(name-service-switch
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(hosts (list %files ;first, check /etc/hosts
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;; If the above did not succeed, try with 'mdns_minimal'.
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(name-service
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(name "mdns_minimal")
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;; 'mdns_minimal' is authoritative for '.local'. When it
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;; returns "not found", no need to try the next methods.
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(reaction (lookup-specification
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(not-found => return))))
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;; Then fall back to DNS.
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(name-service
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(name "dns"))
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;; Finally, try with the "full" 'mdns'.
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(name-service
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(name "mdns"))))))
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;;;
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;;; Serialization.
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;;;
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(define (lookup-status->string status)
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(match status
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('success "SUCCESS")
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('not-found "NOTFOUND")
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('unavailable "UNAVAIL")
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('try-again "TRYAGAIN")
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(($ <lookup-status-negation> status)
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(string-append "!" (lookup-status->string status)))))
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(define lookup-reaction->string
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(match-lambda
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(($ <lookup-reaction> status action)
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(string-append (lookup-status->string status) "="
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(symbol->string action)))))
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(define name-service->string
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(match-lambda
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(($ <name-service> name ())
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name)
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(($ <name-service> name reactions)
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(string-append name " ["
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(string-join (map lookup-reaction->string reactions))
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"]"))))
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(define (name-service-switch->string nss)
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"Return the 'nsswitch.conf' contents for NSS as a string. See \"NSS
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Configuration File\" in the libc manual."
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(let-syntax ((->string
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(syntax-rules ()
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((_ name field)
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(match (field nss)
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(() ;keep the default config
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"")
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((services (... ...))
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(string-append name ":\t"
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(string-join
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(map name-service->string services))
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"\n")))))))
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(string-append (->string "aliases" name-service-switch-aliases)
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(->string "ethers" name-service-switch-ethers)
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(->string "group" name-service-switch-group)
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(->string "gshadow" name-service-switch-gshadow)
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(->string "hosts" name-service-switch-hosts)
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(->string "initgroups" name-service-switch-initgroups)
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(->string "netgroup" name-service-switch-netgroup)
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(->string "networks" name-service-switch-networks)
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(->string "passwd" name-service-switch-password)
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(->string "publickey" name-service-switch-public-key)
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(->string "rpc" name-service-switch-rpc)
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(->string "services" name-service-switch-services)
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(->string "shadow" name-service-switch-shadow))))
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;;; Local Variables:
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;;; eval: (put 'name-service 'scheme-indent-function 0)
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;;; eval: (put 'name-service-switch 'scheme-indent-function 0)
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;;; End:
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;;; nss.scm ends here
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