586 lines
22 KiB
Scheme
586 lines
22 KiB
Scheme
;;; GNU Guix --- Functional package management for GNU
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;;; Copyright © 2019, 2021, 2023 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 build accounts)
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#:use-module (guix records)
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#:use-module (guix combinators)
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#:use-module (gnu system accounts)
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#:use-module (srfi srfi-1)
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#:use-module (srfi srfi-11)
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#:use-module (srfi srfi-19)
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#:use-module (srfi srfi-26)
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#:use-module (ice-9 match)
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#:use-module (ice-9 vlist)
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#:use-module (ice-9 rdelim)
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#:export (password-entry
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password-entry?
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password-entry-name
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password-entry-uid
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password-entry-gid
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password-entry-real-name
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password-entry-directory
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password-entry-shell
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shadow-entry
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shadow-entry?
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shadow-entry-name
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shadow-entry-minimum-change-period
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shadow-entry-maximum-change-period
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shadow-entry-change-warning-time
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shadow-entry-maximum-inactivity
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shadow-entry-expiration
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group-entry
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group-entry?
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group-entry-name
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group-entry-gid
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group-entry-members
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%password-lock-file
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write-group
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write-passwd
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write-shadow
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read-group
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read-passwd
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read-shadow
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%id-min
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%id-max
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%system-id-min
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%system-id-max
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user+group-databases))
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;;; Commentary:
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;;;
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;;; This modules provides functionality equivalent to the C library's
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;;; <shadow.h>, <pwd.h>, and <grp.h> routines, as well as a subset of the
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;;; functionality of the Shadow command-line tools. It can parse and write
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;;; /etc/passwd, /etc/shadow, and /etc/group. It can also take care of UID
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;;; and GID allocation in a way similar to what 'useradd' does.
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;;;
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;;; The benefit is twofold: less code is involved, and the ID allocation
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;;; strategy and state preservation is made explicit.
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;;;
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;;; Code:
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;;;
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;;; Machinery to define user and group databases.
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;;;
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(define-syntax serialize-field
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(syntax-rules (serialization)
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((_ entry (field get (serialization ->string string->) _ ...))
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(->string (get entry)))
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((_ entry (field get _ ...))
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(get entry))))
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(define-syntax deserialize-field
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(syntax-rules (serialization)
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((_ str (field get (serialization ->string string->) _ ...))
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(string-> str))
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((_ str (field get _ ...))
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str)))
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(define-syntax let/fields
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(syntax-rules ()
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((_ (((name get attributes ...) rest ...) lst) body ...)
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(let ((l lst))
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(let ((name (deserialize-field (car l)
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(name get attributes ...))))
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(let/fields ((rest ...) (cdr l)) body ...))))
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((_ (() lst) body ...)
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(begin body ...))))
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(define-syntax define-database-entry
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(syntax-rules (serialization)
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"Define a record data type, as per 'define-record-type*', with additional
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information on how to serialize and deserialize the whole database as well as
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each field."
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((_ <record> record make-record record?
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(serialization separator entry->string string->entry)
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fields ...)
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(let-syntax ((field-name
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(syntax-rules ()
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((_ (name _ (... ...))) name))))
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(define-record-type* <record> record make-record
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record?
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fields ...)
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(define (entry->string entry)
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(string-join (list (serialize-field entry fields) ...)
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(string separator)))
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(define (string->entry str)
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(let/fields ((fields ...) (string-split str #\:))
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(make-record (field-name fields) ...)))))))
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(define number->string*
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(match-lambda
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((? number? number) (number->string number))
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(_ "")))
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(define (false-if-string=? false-string)
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(lambda (str)
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(if (string=? str false-string)
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#f
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str)))
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(define (string-if-false str)
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(lambda (obj)
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(if (not obj) str obj)))
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(define (comma-separated->list str)
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(string-tokenize str (char-set-complement (char-set #\,))))
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(define (list->comma-separated lst)
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(string-join lst ","))
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;;;
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;;; Database definitions.
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;;;
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(define-database-entry <password-entry> ;<pwd.h>
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password-entry make-password-entry
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password-entry?
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(serialization #\: password-entry->string string->password-entry)
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(name password-entry-name)
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(password password-entry-password
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(serialization (const "x") (const #f))
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(default "x"))
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(uid password-entry-uid
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(serialization number->string string->number))
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(gid password-entry-gid
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(serialization number->string string->number))
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(real-name password-entry-real-name
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(default ""))
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(directory password-entry-directory)
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(shell password-entry-shell
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(default "/bin/sh")))
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(define-database-entry <shadow-entry> ;<shadow.h>
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shadow-entry make-shadow-entry
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shadow-entry?
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(serialization #\: shadow-entry->string string->shadow-entry)
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(name shadow-entry-name) ;string
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(password shadow-entry-password ;string | #f
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(serialization (string-if-false "!")
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(false-if-string=? "!"))
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(default #f))
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(last-change shadow-entry-last-change ;days since 1970-01-01
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(serialization number->string* string->number)
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(default 0))
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(minimum-change-period shadow-entry-minimum-change-period
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(serialization number->string* string->number)
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(default #f)) ;days | #f
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(maximum-change-period shadow-entry-maximum-change-period
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(serialization number->string* string->number)
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(default #f)) ;days | #f
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(change-warning-time shadow-entry-change-warning-time
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(serialization number->string* string->number)
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(default #f)) ;days | #f
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(maximum-inactivity shadow-entry-maximum-inactivity
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(serialization number->string* string->number)
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(default #f)) ;days | #f
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(expiration shadow-entry-expiration
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(serialization number->string* string->number)
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(default #f)) ;days since 1970-01-01 | #f
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(flags shadow-entry-flags ;"reserved"
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(serialization number->string* string->number)
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(default #f)))
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(define-database-entry <group-entry> ;<grp.h>
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group-entry make-group-entry
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group-entry?
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(serialization #\: group-entry->string string->group-entry)
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(name group-entry-name)
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(password group-entry-password
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(serialization (string-if-false "x")
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(false-if-string=? "x"))
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(default #f))
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(gid group-entry-gid
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(serialization number->string string->number))
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(members group-entry-members
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(serialization list->comma-separated comma-separated->list)
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(default '())))
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(define %password-lock-file
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;; The password database lock file used by libc's 'lckpwdf'. Users should
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;; grab this lock with 'with-file-lock' when they access the databases.
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"/etc/.pwd.lock")
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(define (database-writer file mode entry->string)
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(lambda* (entries #:optional (file-or-port file))
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"Write ENTRIES to FILE-OR-PORT. When FILE-OR-PORT is a file name, write
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to it atomically and set the appropriate permissions."
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(define (write-entries port)
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(for-each (lambda (entry)
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(display (entry->string entry) port)
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(newline port))
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(delete-duplicates entries)))
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(if (port? file-or-port)
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(write-entries file-or-port)
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(let* ((template (string-append file-or-port ".XXXXXX"))
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(port (mkstemp! template)))
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(dynamic-wind
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(const #t)
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(lambda ()
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(chmod port mode)
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(write-entries port)
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(fsync port)
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(close-port port)
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(rename-file template file-or-port))
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(lambda ()
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(unless (port-closed? port)
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(close-port port))
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(when (file-exists? template)
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(delete-file template))))))))
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(define write-passwd
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(database-writer "/etc/passwd" #o644 password-entry->string))
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(define write-shadow
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(database-writer "/etc/shadow" #o600 shadow-entry->string))
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(define write-group
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(database-writer "/etc/group" #o644 group-entry->string))
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(define (database-reader file string->entry)
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(lambda* (#:optional (file-or-port file))
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(define (read-entries port)
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(let loop ((entries '()))
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(match (read-line port)
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((? eof-object?)
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(reverse entries))
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(line
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(loop (cons (string->entry line) entries))))))
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(if (port? file-or-port)
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(read-entries file-or-port)
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(call-with-input-file file-or-port
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read-entries))))
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(define read-passwd
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(database-reader "/etc/passwd" string->password-entry))
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(define read-shadow
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(database-reader "/etc/shadow" string->shadow-entry))
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(define read-group
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(database-reader "/etc/group" string->group-entry))
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;;;
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;;; Building databases.
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;;;
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(define-record-type* <allocation>
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allocation make-allocation
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allocation?
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(ids allocation-ids (default vlist-null))
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(next-id allocation-next-id (default %id-min))
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(next-system-id allocation-next-system-id (default %system-id-max)))
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;; Trick to avoid name clashes...
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(define-syntax %allocation (identifier-syntax allocation))
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;; Minimum and maximum UIDs and GIDs (from find_new_uid.c and find_new_gid.c
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;; in Shadow.)
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(define %id-min 1000)
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(define %id-max 60000)
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(define %system-id-min 100)
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(define %system-id-max 999)
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(define (system-id? id)
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(and (> id %system-id-min)
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(<= id %system-id-max)))
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(define (user-id? id)
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(and (>= id %id-min)
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(< id %id-max)))
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(define* (allocate-id assignment #:key system?)
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"Return two values: a newly allocated ID, and an updated <allocation> record
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based on ASSIGNMENT. If SYSTEM? is true, return a system ID."
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(define next
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;; Return the next available ID, looping if necessary.
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(if system?
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(lambda (id)
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(let ((next-id (- id 1)))
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(if (< next-id %system-id-min)
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%system-id-max
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next-id)))
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(lambda (id)
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(let ((next-id (+ id 1)))
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(if (>= next-id %id-max)
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%id-min
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next-id)))))
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(let loop ((id (if system?
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(allocation-next-system-id assignment)
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(allocation-next-id assignment))))
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(if (vhash-assv id (allocation-ids assignment))
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(loop (next id))
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(let ((taken (vhash-consv id #t (allocation-ids assignment))))
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(values (if system?
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(allocation (inherit assignment)
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(next-system-id (next id))
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(ids taken))
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(allocation (inherit assignment)
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(next-id (next id))
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(ids taken)))
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id)))))
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(define* (reserve-ids allocation ids #:key (skip? #t))
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"Mark the numbers listed in IDS as reserved in ALLOCATION. When SKIP? is
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true, start allocation after the highest (or lowest, depending on whether it's
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a system ID allocation) number among IDS."
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(%allocation
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(inherit allocation)
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(next-id (if skip?
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(+ (reduce max
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(- (allocation-next-id allocation) 1)
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(filter user-id? ids))
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1)
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(allocation-next-id allocation)))
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(next-system-id
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(if skip?
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(- (reduce min
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(+ 1 (allocation-next-system-id allocation))
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(filter system-id? ids))
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1)
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(allocation-next-system-id allocation)))
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(ids (fold (cut vhash-consv <> #t <>)
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(allocation-ids allocation)
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ids))))
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(define (allocated? allocation id)
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"Return true if ID is already allocated as part of ALLOCATION."
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(->bool (vhash-assv id (allocation-ids allocation))))
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(define (lookup-procedure lst key)
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"Return a lookup procedure for the elements of LST, calling KEY to obtain
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the key of each element."
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(let ((table (fold (lambda (obj table)
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(vhash-cons (key obj) obj table))
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vlist-null
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lst)))
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(lambda (key)
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(match (vhash-assoc key table)
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(#f #f)
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((_ . value) value)))))
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(define* (allocate-groups groups members
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#:optional (current-groups '()))
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"Return a list of group entries for GROUPS, a list of <user-group>. Members
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for each group are taken from MEMBERS, a vhash that maps group names to member
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names. GIDs and passwords found in CURRENT-GROUPS, a list of group entries,
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are reused."
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(define gids
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;; Mark all the currently-used GIDs and the explicitly requested GIDs as
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;; reserved.
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(reserve-ids (reserve-ids (allocation)
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(map group-entry-gid current-groups))
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(filter-map user-group-id groups)
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#:skip? #f))
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(define previous-entry
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(lookup-procedure current-groups group-entry-name))
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(reverse
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(fold2 (lambda (group result allocation)
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(let ((name (user-group-name group))
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(password (user-group-password group))
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(requested-id (user-group-id group))
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(system? (user-group-system? group)))
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(let*-values (((previous)
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(previous-entry name))
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((allocation id)
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(cond
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((number? requested-id)
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(values (reserve-ids allocation
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(list requested-id))
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requested-id))
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(previous
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(values allocation
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(group-entry-gid previous)))
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(else
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(allocate-id allocation
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#:system? system?)))))
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(values (cons (group-entry
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(name name)
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(password
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(if previous
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(group-entry-password previous)
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password))
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(gid id)
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(members (vhash-fold* cons '() name members)))
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result)
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allocation))))
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'()
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gids
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groups)))
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(define* (allocate-passwd users groups #:optional (current-passwd '()))
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"Return a list of password entries for USERS, a list of <user-account>.
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Take GIDs from GROUPS, a list of group entries. Reuse UIDs from
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CURRENT-PASSWD, a list of password entries, when possible; otherwise allocate
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new UIDs."
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(define uids
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(reserve-ids (reserve-ids (allocation)
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(map password-entry-uid current-passwd))
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(filter-map user-account-uid users)
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#:skip? #f))
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(define previous-entry
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(lookup-procedure current-passwd password-entry-name))
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(define (group-id name)
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(or (any (lambda (entry)
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(and (string=? (group-entry-name entry) name)
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(group-entry-gid entry)))
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groups)
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(error "group not found" name)))
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(reverse
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(fold2 (lambda (user result allocation)
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(let ((name (user-account-name user))
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(requested-id (user-account-uid user))
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(group (user-account-group user))
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(real-name (user-account-comment user))
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(directory (user-account-home-directory user))
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(shell (user-account-shell user))
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(system? (user-account-system? user)))
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(let*-values (((previous)
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(previous-entry name))
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((allocation id)
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(cond
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((number? requested-id)
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(values (reserve-ids allocation
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(list requested-id))
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requested-id))
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(previous
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(values allocation
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(password-entry-uid previous)))
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(else
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(allocate-id allocation
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#:system? system?)))))
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(values (cons (password-entry
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(name name)
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(uid id)
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(directory directory)
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(gid (if (number? group) group (group-id group)))
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;; Users might change their name to something
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;; other than what the sysadmin chose, with
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;; 'chfn'. Thus consider it "stateful".
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(real-name (if (and previous (not system?))
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(password-entry-real-name previous)
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real-name))
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;; Do not reuse the shell of PREVIOUS since (1)
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;; that could lead to confusion, and (2) the
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;; shell might have been GC'd. See
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;; <https://lists.gnu.org/archive/html/guix-devel/2019-04/msg00478.html>.
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(shell shell))
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result)
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allocation))))
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'()
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uids
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users)))
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(define* (days-since-epoch #:optional (current-time current-time))
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"Return the number of days elapsed since the 1st of January, 1970."
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(let* ((now (current-time time-utc))
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(epoch (make-time time-utc 0 0))
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(diff (time-difference now epoch)))
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(quotient (time-second diff) (* 24 3600))))
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(define* (passwd->shadow users passwd #:optional (current-shadow '())
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#:key (current-time current-time))
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"Return a list of shadow entries for the password entries listed in PASSWD.
|
||
Reuse shadow entries from CURRENT-SHADOW when they exist, and take the initial
|
||
password from USERS."
|
||
(define previous-entry
|
||
(lookup-procedure current-shadow shadow-entry-name))
|
||
|
||
(define now
|
||
;; On machines without a real-time clock (typically Arm SBCs), the system
|
||
;; clock may be at 1970-01-01 while booting, which would lead us to define
|
||
;; NOW as zero.
|
||
;;
|
||
;; However, the 'isexpired' function in Shadow interprets the combination
|
||
;; uninitialized password + last-change = 0 as "The password has expired,
|
||
;; it must be changed", which prevents logins altogether. To avoid that,
|
||
;; never set 'last-change' to zero.
|
||
(max (days-since-epoch current-time) 1))
|
||
|
||
(map (lambda (user passwd)
|
||
(or (previous-entry (password-entry-name passwd))
|
||
(shadow-entry (name (password-entry-name passwd))
|
||
(password (user-account-password user))
|
||
(last-change now))))
|
||
users passwd))
|
||
|
||
(define (empty-if-not-found thunk)
|
||
"Call THUNK and return the empty list if that throws to ENOENT."
|
||
(catch 'system-error
|
||
thunk
|
||
(lambda args
|
||
(if (= ENOENT (system-error-errno args))
|
||
'()
|
||
(apply throw args)))))
|
||
|
||
(define* (user+group-databases users groups
|
||
#:key
|
||
(current-passwd
|
||
(empty-if-not-found read-passwd))
|
||
(current-groups
|
||
(empty-if-not-found read-group))
|
||
(current-shadow
|
||
(empty-if-not-found read-shadow))
|
||
(current-time current-time))
|
||
"Return three values: the list of group entries, the list of password
|
||
entries, and the list of shadow entries corresponding to USERS and GROUPS.
|
||
Preserve stateful bits from CURRENT-PASSWD, CURRENT-GROUPS, and
|
||
CURRENT-SHADOW: UIDs, GIDs, passwords, user shells, etc."
|
||
(define members
|
||
;; Map group name to user names.
|
||
(fold (lambda (user members)
|
||
(fold (cute vhash-cons <> (user-account-name user) <>)
|
||
members
|
||
(user-account-supplementary-groups user)))
|
||
vlist-null
|
||
users))
|
||
|
||
(define group-entries
|
||
(allocate-groups groups members current-groups))
|
||
|
||
(define passwd-entries
|
||
(allocate-passwd users group-entries current-passwd))
|
||
|
||
(define shadow-entries
|
||
(passwd->shadow users passwd-entries current-shadow
|
||
#:current-time current-time))
|
||
|
||
(values group-entries passwd-entries shadow-entries))
|