1SYSCONFTOOL(7) sysconftool SYSCONFTOOL(7)
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6 sysconftool - format of configuration files installed by sysconftool
7
9 #
10 ##VERSION: $Id$
11 ##NAME: configname1:configname1version
13 #
14 # Description
15 SETTING1=VALUE1
17 ##NAME: configname2:configname2version
19 #
20 # Description
21 SETTING2=VALUE2
23 ...
25
27 This manual page describes the format of configuration files installed
28 by sysconftool(1)[1]. This format is flexible enough to accomodate any
29 kind of application configuration file format. sysconftool makes four
30 assumptions about the configuration file:
31 1. It is a plain text file.
33 2. Lines that begin with a single '#' character are comments that
35 contain a description of the following configuration setting.
36 3. Lines that do not begin with the '#' character contain the
38 configuration setting described by the previous comment lines.
39 4. Configuration settings are self contained, and completely
41 independent, changing one configuration setting never requires that
42 another, different, configuration setting must be changed too
43 (perhaps any logical conflicts are automatically resolved by the
44 application in a safe, fallback, manner)
45 The additional information used by sysconftool is encoded as
47 specially-formatted comment lines that begin with two '#' characters.
48
50 An application installs a default configuration file as
51 "filename.dist", when the actual name of the configuration file is
52 really "filename". If there is no existing filename, sysconftool simply
53 copies filename.dist to filename, and calls it a day. Otherwise,
54 sysconftool copies the existing filename to filename.bak and creates a
55 new filename based on the contents of both files.
56 sysconftool is designed to solve a common problem with application
58 configuration. New versions of applications often include additional
59 functionality that requires new configuration settings. Without the new
60 configuration settings the application will not work, so new
61 configuration files should be installed during the upgrade. However,
62 when that happens, any changes to the existing configuration settings
63 are lost. sysconftool is designed to solve this dillemma, and merge
64 old configuration settings with new ones. sysconftool is designed in a
65 fail-safe way. Whenever there's a doubt as to what's The Right Thing To
66 Do, sysconftool will use the configuration settings from the new file,
67 that are supposedly known to be good, and leave it up to a physical
68 being to sort out any conflicts and make any manual decisions.
69
71 The following line should appear at the beginning of filename.dist:
72 ##VERSION: version
74 This doesn't have to be the very first line in filename.dist, but it
76 should appear somewhere within the first twenty lines, right before the
77 first configuration setting. "version" should be some kind of an
78 identifier for this particular version of the configuration files. All
79 that sysconftool cares about is that any change to the default
80 configuration, in filename.dist, results in a different version. An
81 excellent way to do this is to simply use the $Id$ RCS/CVS version
82 identification strings, and have this little detail taken care of
83 automatically.
84 New revisions of an application should not necessarily have a new
86 configuration file version. If the default application configuration
87 settings have not changed from the previous release, version can remain
88 the same. version is copied from filename.dist to filename.
89 If there's an existing filename, and it includes the same version
91 identifier, sysconftool silently skips over this configuration file,
92 and doesn't do anything, assuming that this configuration file has
93 already been installed. Therefore, running sysconftool more than once
94 (accidentally) will not break anything.
95 If there's an existing filename, but it's version is different,
97 sysconftool backs it up to filename.bak, then creates a new filename.
98 If there's an existing filename, but it doesn't contain a recognizable
99 "##VERSION: version" line, sysconftool assumes that the previous
100 version of the application did not use the sysconftool tool. That's not
101 a problem. filename is copied to filename.bak, and filename.dist gets
102 installed as the new filename, allowing sysconftool to work with the
103 next version of this configuration file.
104
106 Each configuration setting uses the following format in the
107 configuration file:
108 ##NAME: name:revision
110 #
111 # description
112 setting
114 sysconftool looks for a line that begins with "##NAME". This line gives
116 the name and the revision of the following setting. name must be
117 unique within its configuration file (the same name can be used by
118 different configuration files, sysconftool works with one file at a
119 time). revision is used by sysconftool to decide when the
120 configuration setting can be safely carried over from an older
121 configuration file, and when it is better to reinstall the default
122 setting from the new configuration file.
123 One or more comment lines - lines that begin with the '#' character -
125 may follow "##NAME". The first line that does not begin with '#' is
126 considered to be the first line that contains the value of the
127 configuration setting, which lasts. The value can be spread over
128 multiple lines. The configuration setting is considered to last until
129 either the end of the file, or until the first following line that
130 begins with another "##NAME".
131 Aside from that, sysconftool does not care how the configuration
133 setting is represented. It can be "NAME=VALUE", it can be "NAME:
134 VALUE", or "NAME<tab>VALUE", it can even be a base64-encoded binary
135 object, and it can always have leading or trailing blank lines.
136 sysconftool merely looks at which lines begin with the '#' comment
137 character. After the '##NAME:' line, sysconftool looks ahead until the
138 first line that does not begin with '#', and that's the first line of
139 the configuration setting. Then, sysconftool looks ahead until the next
140 line that starts with a "##NAME:", which marks the end of this
141 configuration setting.
142 For this reason it is important that all commented description lines
144 that follow '##NAME:' must begin with the '#' character. If a blank
145 line follows the line with '##NAME:' it is assumed to be the start of
146 the corresponding configuration setting. For example, this is correct:
147 ##NAME: flag1:0
149 #
150 #
151 # This is the first configuration flag
152 #
153 flag1=1
155 This is not correct:
157 ##NAME: flag1:0
159 #
161 # This is the first configuration flag
162 #
163 flag1=1
165
167 A new configuration file, "filename", is created from its previous
168 version, "filename.bak" and the new default configuration file,
169 "filename.dist", using the following, simple, two-step process.
170 1. sysconftool begins with filename.dist in hand. This makes sure that
172 sysconftool begins with a good, known, default configuration file.
173 2. sysconftool then takes each configuration setting in filename.dist,
175 then searches filename.bak. If it finds a configuration setting
176 that has an identical "name" and "version", then the corresponding
177 configuration setting value is taken from filename.bak, replacing
178 the default in filename.dist. After all configuration settings in
179 filename.dist are looked up (and potentially replaced), what's left
180 becomes the new filename.
181
183 The above process is a logical description. The actual technical
184 implementation is slightly different (for example, filename is not
185 backed up to filename.bak until the new configuration file has been
186 already created), but is logically equivalent to this process. This
187 process carries a number of consequences that must be considered.
188 If a new application revision needs a new configuration setting, it
190 will get a new name and version. Since filename.dist is used as a
191 starting point for the new configuration file, the new configuration
192 file will include the new configuration setting. When a configuration
193 setting is removed, it will disappear from the new configuration file
194 for the same exact reason.
195
197 sysconftool looks at both name and version. A configuration setting
198 with the same name but different versions are seen by sysconftool as
199 completely different settings. The existence of version allows a
200 finer-grained control of configuration upgrades, as described below.
201 sysconftool copies setting values with the same name and version from
203 the old configuration file to the new configuration file. However, the
204 associated descriptive comments are not copied, and are taken from the
205 new filename.dist. Therefore, if a new version of the configuration
206 file contains an updated or an embellished description of a particular
207 setting, it will be included in the new configuration file, but the
208 existing configuration value will be preserved! Generally, if a
209 configuration setting does not change its meaning or function, its name
210 and version should remain the same. Its comments can be edited to fix a
211 typo, or revised in a more substantive fashion. Name and version
212 should only be changed if there's a functional change in the
213 configuration setting.
214 What to do with name and version after a functional change depends on
216 the nature and the magnitude of the change. The nature and the
217 magnitude of the change must be considered not only with respect to the
218 most recent revision of the application, but to all the previous
219 revisions as well. When in doubt, go based upon the largest change in
220 magnitude, in order to guarantee a functional default setting, from
221 filename.dist, and leave it up to a living being to manually figure it
222 out.
223 If only the default value of a setting should be changed for new
225 application installation, but the existing installations can continue
226 to use the existing value of the setting, both the name and version
227 should be left alone. Existing configuration settings will be
228 preserved, and new installations will get the new default. The
229 descriptive comment of this setting can be updated too (see above).
230 This should be done only as long as ALL previous values of this
232 configuration setting will ALWAYS be valid in the new application
233 revision. If some possible values of this configuration setting will no
234 longer be valid, version should be changed. sysconftool does not care
235 how name and version are formatted. Both are opaque labels. The only
236 requirements is for the label to be different. The difference between
237 changing version and changing both name and version is this:
238 If there's an old configuration setting with the same name but
240 different version, sysconftool will still use the new, safe, default
241 value from filename.dist, however sysconftool will also append an
242 additional comment, on its own accord, reminding the reader that this
243 configuration value has been reset, and the reader should consider
244 whether to manually restore the configuration value from the old
245 configuration.
246
248 When sysconftool decides to keep an existing setting, with the same
249 name and value, it will also insert a short comment to that effect,
250 reminding the reader to check the default in filename.dist.
251
253 sysconftool(1)[1].
254
256 Double Precision, Inc.
257
259 1. sysconftool(1)
260 [set $man.base.url.for.relative.links]/sysconftool.1.html
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