1DEBCONF(7) Miscellaneous Information Manual DEBCONF(7)
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6 debconf - Debian package configuration system
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9 Debconf is a configuration system for Debian packages. There is a
10 rarely-used command named debconf, documented in debconf(1)
11 Debconf provides a consistent interface for configuring packages,
13 allowing you to choose from several user interface frontends. It sup‐
14 ports preconfiguring packages before they are installed, which allows
15 large installs and upgrades to ask you for all the necessary informa‐
16 tion up front, and then go do the work while you do something else. It
17 lets you, if you're in a hurry, skip over less important questions and
18 information while installing a package (and revisit it later).
19
21 Debconf can configure packages before they are even installed onto your
22 system. This is useful because it lets all the questions the packages
23 are going to ask be asked at the beginning of an install, so the rest
24 of the install can proceed while you are away getting a cup of coffee.
25 If you use apt (version 0.5 or above), and you have apt-utils
27 installed, each package apt installs will be automatically preconfig‐
28 ured. This is controlled via /etc/apt/apt.conf.d/70debconf
29 Sometimes you might want to preconfigure a package by hand, when you're
31 not installing it with apt. You can use dpkg-preconfigure(8) to do
32 that, just pass it the filenames of the packages you want to preconfig‐
33 ure. You will need apt-utils installed for that to work.
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36 Suppose you installed the package, and answered debconf's questions,
37 but now that you've used it awhile, you realize you want to go back and
38 change some of your answers. In the past, reinstalling a package was
39 often the thing to do when you got in this situation, but when you
40 reinstall the package, debconf seems to remember you have answered the
41 questions, and doesn't ask them again (this is a feature).
42 Luckily, debconf makes it easy to reconfigure any package that uses it.
44 Suppose you want to reconfigure debconf itself. Just run, as root:
45 dpkg-reconfigure debconf
46 This will ask all the questions you saw when debconf was first
48 installed. It may ask you other questions as well, since it asks even
49 low priority questions that may have been skipped when the package was
50 installed. You can use it on any other package that uses debconf, as
51 well.
52
54 One of debconf's unique features is that the interface it presents to
55 you is only one of many, that can be swapped in at will. There are many
56 debconf frontends available:
57 dialog The default frontend, this uses the whiptail(1) or dialog(1)
59 programs to display questions to you. It works in text mode.
60 readline
62 The most traditional frontend, this looks quite similar to how
63 Debian configuration always has been: a series of questions,
64 printed out at the console using plain text, and prompts done
65 using the readline library. It even supports tab completion. The
66 libterm-readline-gnu-perl package is strongly recommended if you
67 chose to use this frontend; the default readline module does not
68 support prompting with default values. At the minimum, you'll
69 need the perl-modules package installed to use this frontend.
70 This frontend has some special hotkeys. Pageup (or ctrl-u) will
72 go back to the previous question (if that is supported by the
73 package that is using debconf), and pagedown (or ctrl-v) will
74 skip forward to the next question.
75 This is the best frontend for remote admin work over a slow con‐
77 nection, or for those who are comfortable with unix.
78 noninteractive
80 This is the anti-frontend. It never interacts with you at all,
81 and makes the default answers be used for all questions. It
82 might mail error messages to root, but that's it; otherwise it
83 is completely silent and unobtrusive, a perfect frontend for
84 automatic installs. If you are using this front-end, and require
85 non-default answers to questions, you will need to preseed the
86 debconf database; see the section below on Unattended Package
87 Installation for more details.
88 gnome This is a modern X GUI using the gtk and gnome libraries. Of
90 course, it requires a valid DISPLAY to work; debconf will fall
91 back to other frontends if it can't work. Note that this fron‐
92 tend requires you have the libgtk3-perl package installed.
93 kde This frontend provides a modern X GUI based on the KDE Platform.
95 You of course need a DISPLAY to use this frontend and you must
96 install debconf-kde-helper package. The frontend will fall back
97 to dialog if some of the prerequisites are not met.
98 editor This is for those fanatics who have to do everything in a text
100 editor. It runs your editor on a file that looks something like
101 a typical unix config file, and you edit the file to communicate
102 with debconf. Debconf's author prefers to not comment regarding
103 the circumstances that led to this frontend being written.
104 web
106 This frontend acts as a web server, that you connect to with
107 your web browser, to browse the questions and answer them. It
108 has a lot of promise, but is a little rough so far. When this
109 frontend starts up, it will print out the location you should
110 point your web browser to. You have to run the web browser on
111 the same machine you are configuring, for security reasons.
112 Do keep in mind that this is not a very secure frontend. Anyone
114 who has access to the computer being configured can currently
115 access the web server and configure things while this frontend
116 is running. So this is more of a proof of concept than anything.
117 You can change the default frontend debconf uses by reconfiguring deb‐
119 conf. On the other hand, if you just want to change the frontend for a
120 minute, you can set the DEBIAN_FRONTEND environment variable to the
121 name of the frontend to use. For example:
122 DEBIAN_FRONTEND=readline apt-get install slrn
123 The dpkg-reconfigure(8) and dpkg-preconfigure(8) commands also let you
125 pass --frontend= to them, followed by the frontend you want them to
126 use.
127 Note that not all frontends will work in all circumstances. If a fron‐
129 tend fails to start up for some reason, debconf will print out a mes‐
130 sage explaining why, and fall back to the next-most similar frontend.
131
133 Another nice feature of debconf is that the questions it asks you are
134 prioritized. If you don't want to be bothered about every little thing,
135 you can set up debconf to only ask you the most important questions.
136 On the other hand, if you are a control freak, you can make it show you
137 all questions. Each question has a priority. In increasing order of
138 importance:
139 low Very trivial questions that have defaults that will work in the
141 vast majority of cases.
142 medium Normal questions that have reasonable defaults.
144 high Questions that don't have a reasonable default.
146 critical
148 Questions that you really, really need to see (or else).
149 Only questions with a priority equal to or greater than the priority
151 you choose will be shown to you. You can set the priority value by
152 reconfiguring debconf, or temporarily by passing --priority= followed
153 by the value to the dpkg-reconfigure(8) and dpkg-preconfigure(8) com‐
154 mands, or by setting the DEBIAN_PRIORITY environment variable.
155
157 Debconf uses a rather flexible and potentially complicated backend
158 database for storing data such as the answers to questions. The file
159 /etc/debconf.conf is used to configure this database. If you need to
160 set up something complicated, like make debconf read a remote database
161 to get defaults, with local overrides, read the debconf.conf(5) man
162 page for all the gory details. Generally, the backend database is
163 located in /var/cache/debconf/
164 .
165
167 If you have many machines to manage you will sometimes find yourself in
168 the position of needing to perform an unattended installation or
169 upgrade of packages on many systems, when the default answers to some
170 configuration questions are not acceptable. There are many ways to
171 approach this; all involve setting up a database and making debconf use
172 it to get the answers you want.
173 You should really read debconf.conf(5) before this section, as you need
175 to understand how debconf's databases work.
176 The easiest way to set up the database is to install the packages on
178 one machine and answer their questions as usual. Or you might just use
179 dpkg-preconfigure(8) to configure a set of packages without actually
180 installing them. Or you might even decide to write a plain text debconf
181 database by hand or something.
182 Once you have the database, you need to figure out how to make the
184 remote systems use it. This depends of course on the configuration of
185 those systems and what database types they are set up to use.
186 If you are using the LDAP debconf database, an entire network of debian
188 machines can also have any or all package installation questions
189 answered automatically by a single LDAP server.
190 But perhaps you're using something a little bit easier to set up like,
192 say, the default debconf database configuration, or you just don't want
193 your remote systems to use LDAP all the time. In this case the best
194 approach is to temporarily configure the remote systems to stack your
195 database underneath their own existing databases, so they pull default
196 values out of it. Debconf offers two environment variables, DEB‐
197 CONF_DB_FALLBACK and DEBCONF_DB_OVERRIDE, to make it easy to do this on
198 the fly. Here is a sample use:
199 cat /var/cache/debconf/config.dat | \
201 ssh root@target "DEBIAN_FRONTEND=noninteractive \
202 DEBCONF_DB_FALLBACK=Pipe apt-get upgrade"
203 This makes the debconf on the remote host read in the data that is
205 piped across the ssh connection and interpret it as a plain text format
206 debconf database. It then uses that database as a fallback database --
207 a read-only database that is queried for answers to questions if the
208 system's main debconf database lacks answers.
209 Here's another way to use the DEBCONF_DB_FALLBACK environment variable:
211 ssh -R 389:ldap:389 root@target \
213 "DEBCONF_DB_FALLBACK='LDAP{host:localhost}' apt-get upgrade"
214 Here ssh is used to set up a tunneled LDAP connection and run debconf.
216 Debconf is told to use the LDAP server as the fallback database. Note
217 the use of "{host:localhost}" to configure how debconf accesses the
218 LDAP database by providing the "host" field with a value of "local‐
219 host".
220 Here's another method:
222 scp config.dat root@target:
224 ssh root@target "DEBCONF_DB_FALLBACK='File{/root/config.dat}' apt-get
225 upgrade
226 Here you copy the database over with scp, and then ssh over and make
228 debconf use the file you copied over. This illustrates a shorthand you
229 can use in the DEBCONF_DB_FALLBACK parameters -- if a field name is
230 left off, it defaults to "filename".
231 There is only one problem with these uses of the DEBCONF_DB_FALLBACK
233 parameter: While the fallback database can provide answers to questions
234 the other debconf databases have never seen, it is only queried as a
235 fallback; after the other databases. If you need to instead temporarily
236 override an existing value on the remote host, you should instead use
237 the DEBCONF_DB_OVERRIDE variable. Like DEBCONF_DB_FALLBACK, it sets up
238 a temporary database, but this database is consulted before any others,
239 and can be used to override existing values.
240
242 Package developers and others who want to develop packages that use
243 debconf should read debconf-devel(7)
244 .
245 Briefly, debconf communicates with maintainer scripts or other programs
247 via standard input and output, using a simple line-oriented command
248 language similar to that used by common internet protocols such as
249 SMTP. Programs use this protocol to ask debconf to display questions to
250 the user, and retrieve the user's answers. The questions themselves are
251 defined in a separate file, called the "templates file", which has a
252 format not unlike a debian control file.
253 Debian packages which use debconf typically provide both a templates
255 file and a "config" script (run to preconfigure the package) in the
256 control metadata section of the package.
257
259 DEBIAN_FRONTEND
260 Used to temporarily change the frontend debconf uses. See above.
261 DEBIAN_PRIORITY
263 Used to temporarily change the minimum priority of question deb‐
264 conf will display. See above.
265 DEBCONF_DEBUG
267 Turns on debugging output on standard error. May be set to a
268 facility name or a regular expression which matches a facility
269 name (such as '.*' to output all debug info). The facility names
270 include:
271 user Debugging info of interest to a debconf user.
273 developer
275 Debugging info of interest to a package developer.
276 db Debugging info about the backend database.
278 DEBCONF_NOWARNINGS
280 Set to "yes" to disable some warnings that debconf may display.
281 Does not suppress display of fatal errors.
282 DEBCONF_TERSE
284 Set to "yes" to enable terse mode, in which debconf frontends
285 cut down on the verbiage as much as possible.
286 DEBCONF_DB_FALLBACK
288 Stack a database after the normally used databases, so that it
289 is used as a fallback to get configuration information from. See
290 "Unattended Package Installation" above. If the value of the
291 variable is the name of an existing database in debconf.conf,
292 then that database will be used. Otherwise, the environment
293 variable can be used to configure a database on the fly, by
294 telling the type of database, and optionally passing field:value
295 settings, inside curly braces after the type. Spaces are used to
296 separate fields, so you cannot specify a field value containing
297 whitespace.
298 Thus, this uses the fallbackdb in debconf.conf:
300 DEBCONF_DB_FALLBACK=fallbackdb
301 While this sets up a new database of type File, and tells it a filename
303 to use and turns off backups:
304 DEBCONF_DB_FALLBACK=File{Filename:/root/config.dat Backup:no}
305 And as a shorthand, this sets up a database of type File with a file‐
307 name:
308 DEBCONF_DB_FALLBACK=File{/root/config.dat}
309 Note that if a fallback database is set up on the fly, it will be read-
311 only by default.
312 DEBCONF_DB_OVERRIDE
314 Stack a database before the normally used databases, so that it
315 can override values from them. The value of the variable works
316 the same as does the value of DEBCONF_DB_FALLBACK.
317 DEBCONF_DB_REPLACE
319 Use a given database instead of the normally used databases.
320 This may be useful for testing with a separate database without
321 having to create a separate debconf.conf, or to avoid locking
322 the normal databases.
323 DEBCONF_SYSTEMRC
325 If this environment variable is set, debconf will ignore a
326 user's ~/.debconfrc file, and use the system one instead. If it
327 is set to the name of a regular file, debconf will use that file
328 in preference to the system configuration files.
329 DEBCONF_FORCE_DIALOG
331 If this environment variable is set, debconf will use dialog in
332 preference to whiptail for the dialog frontend.
333 DEBCONF_FORCE_XDIALOG
335 If this environment variable is set, debconf will use Xdialog in
336 preference to whiptail for the dialog frontend.
337 DEBCONF_NONINTERACTIVE_SEEN
339 Set to "true" to cause the seen flag to be set for questions
340 asked in the noninteractive frontend.
341
343 Probably quite a few, there's a lot of code here.
344 If you do file a bug report, be sure to include the following informa‐
346 tion:
347 * The debconf frontend you were using when the problem occurred
349 * What you did to trigger the problem.
351 * The full text of any error messages. If you can reproduce the
353 bug, do so with DEBCONF_DEBUG='.*' set and exported. This speeds
354 up debugging a lot.
355
357 debconf.conf(5), debconf-devel(7), dpkg-preconfigure(8), dpkg-reconfig‐
358 ure(8), debconf(1),
359
361 Joey Hess <joeyh@debian.org>
362 DEBCONF(7)