.\"<!-- $Id: sysconftool7.sgml,v 1.2 2005/07/16 18:37:24 mrsam Exp $ -->
.\"<!-- Copyright 2000-2005 Double Precision, Inc.  See COPYING for -->
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.TH "SYSCONFTOOL" "7" "16 July 2005" "Double Precision, Inc." ""

.SH NAME
sysconftool \- format of configuration files installed by sysconftool
.SH SYNOPSIS
.PP

.nf
   #
   ##VERSION: $Id$

   ##NAME: configname1:configname1version
   #
   # Description

   SETTING1=VALUE1

   ##NAME: configname2:configname2version
   #
   # Description

   SETTING2=VALUE2

   ...
.fi
.SH "DESCRIPTION"
.PP
This manual page describes the format of configuration files installed by
\fBsysconftool\fR(1)\&.
This format is flexible enough to accomodate any
kind of application configuration file format.
\fBsysconftool\fR makes
four assumptions about the configuration file:
.TP 3
1. 
It is a plain text file.
.TP 3
2. 
Lines that begin with a single '#' character are comments that
contain a description of the following configuration setting.
.TP 3
3. 
Lines that do not begin with the '#' character contain the configuration
setting described by the previous comment lines.
.TP 3
4. 
Configuration settings are self contained, and completely independent,
changing one configuration setting never requires that another, different,
configuration setting must be changed too (perhaps any logical conflicts are
automatically resolved by the application in a safe, fallback, manner)
.PP
The additional information used by \fBsysconftool\fR is encoded as
specially-formatted comment lines that begin with two '#' characters.
.SH "FILENAMES"
.PP
An application installs a default configuration file as
"\fIfilename.dist\fR", when the actual name of the
configuration file is
really "\fIfilename\fR". If there is no existing
\fIfilename\fR,
\fBsysconftool\fR simply copies
\fIfilename.dist\fR to
\fIfilename\fR, and calls it a day. Otherwise,
\fBsysconftool\fR
copies the existing \fIfilename\fR to \fIfilename.bak\fR and creates a new
\fIfilename\fR based on the contents of both files.
.PP
\fBsysconftool\fR is designed to solve a common problem with
application configuration.  New versions of applications often include
additional functionality that requires new configuration settings. Without the
new configuration settings the application will not work, so new configuration
files should be installed during the upgrade.  However, when that happens, any
changes to the existing configuration settings are lost.
\fBsysconftool\fR is designed to solve this dillemma, and
merge old
configuration settings with new ones. \fBsysconftool\fR
is designed in
a fail-safe way. Whenever there's a doubt as to what's The Right Thing To
Do, \fBsysconftool\fR will use the configuration settings
from the
new file, that are supposedly known to be good, and leave it up to a physical
being to sort out any conflicts and make any manual decisions.
.SH "FILE VERSIONING"
.PP
The following line should appear at the beginning of
\fIfilename.dist\fR:
.PP

.nf
   ##VERSION: \fIversion\fR
.fi
.PP
This doesn't have to be the very first line in
\fIfilename.dist\fR, but it
should appear somewhere within the first twenty lines, right before the first
configuration setting. "\fIversion\fR" should be some kind
of an identifier
for this particular version of the configuration files. All that
\fBsysconftool\fR cares about is that any change to the default
configuration, in \fIfilename.dist\fR, results in a different
\fIversion\fR\&.
An excellent way to do this is to simply use the $Id$
RCS/CVS version identification strings, and have this little detail taken care
of automatically.
.PP
New revisions of an application should not necessarily have a new
configuration file \fIversion\fR\&.  If the default
application configuration
settings have not changed from the previous release,
\fIversion\fR can remain
the same. \fIversion\fR is copied from
\fIfilename.dist\fR to
\fIfilename\fR\&.
.PP
If there's an existing \fIfilename\fR, and it
includes the same
\fIversion\fR identifier, \fBsysconftool\fR
silently skips over this
configuration file, and doesn't do anything, assuming that this configuration
file has already been installed.  Therefore,
running \fBsysconftool\fR
more than once (accidentally) will not break anything.
.PP
If there's an existing \fIfilename\fR, but it's
\fIversion\fR is
different, \fBsysconftool\fR backs it up to
\fIfilename.bak\fR, then
creates a new \fIfilename\fR\&.
If there's
an existing \fIfilename\fR, but it doesn't contain a
recognizable "##VERSION:
\fIversion\fR" line, \fBsysconftool\fR
assumes that the previous
version of the application did not use the \fBsysconftool\fR tool.
That's not a problem. \fIfilename\fR is copied
to \fIfilename.bak\fR, and
\fIfilename.dist\fR gets installed as the new
\fIfilename\fR, allowing
\fBsysconftool\fR to work with the next version
of this configuration file.
.SH "CONFIGURATION SETTING VERSIONING"
.PP
Each configuration setting uses the following format in the configuration
file:
.PP

.nf
   ##NAME: \fIname\fR:\fIrevision\fR
   #
   # \fIdescription\fR

   \fIsetting\fR
.fi
.PP
\fBsysconftool\fR
looks for a line that begins with "##NAME". This line
gives the name and the revision of the following setting.
\fIname\fR must be
unique within its configuration file (the same
\fIname\fR can be used by
different configuration files, \fBsysconftool\fR works with
one file at
a time). \fIrevision\fR is used by
\fBsysconftool\fR to decide when
the configuration setting can be safely carried over from an older
configuration file, and when it is better to reinstall the default setting
from the new configuration file.
.PP
One or more comment lines - lines that begin with the '#' character - may
follow "##NAME".  The first line that does not begin with '#' is considered to
be the first line that contains the value of the configuration setting, which
lasts. The value can be spread over multiple lines.  The configuration setting
is considered to last until either the end of the file, or until the first
following line that begins with another "##NAME".
.PP
Aside from that, \fBsysconftool\fR does not care how the
configuration setting is represented.  It can be
"NAME=VALUE", it can be
"NAME: VALUE",
or "NAME<tab>VALUE", it can even be a base64-encoded
binary object, and it can always have leading or trailing blank lines.
\fBsysconftool\fR merely looks at which lines begin with the '#'
comment character.  After the
\&'##NAME:\&' line, \fBsysconftool\fR looks
ahead until the first line that does not begin with '#', and that's the first
line of the configuration setting.
Then, \fBsysconftool\fR looks ahead
until the next line that starts with a
"##NAME:", which marks the end of this
configuration setting.
.PP
For this reason it is important that all commented description lines that
follow '##NAME:\&' must begin with the '#' character.
If a blank line follows
the line with '##NAME:\&' it is assumed to be the start of
the corresponding
configuration setting.  For example, this is correct:
.PP

.nf
   ##NAME: flag1:0
   #
   #
   # This is the first configuration flag
   #

   flag1=1
.fi
.PP
This is not correct:
.PP

.nf
   ##NAME: flag1:0

   #
   # This is the first configuration flag
   #

   flag1=1
.fi
.SH "CONFIGURATION FILE CREATION"
.PP
A new configuration file, "\fIfilename\fR", is created
from its previous
version, "\fIfilename.bak\fR" and the new default
configuration file,
"\fIfilename.dist\fR", using the following, simple, two-step
process.
.TP 3
1. 
\fBsysconftool\fR begins with \fIfilename.dist\fR
in hand. This
makes sure that \fBsysconftool\fR begins with a good, known,
default configuration file.
.TP 3
2. 
\fBsysconftool\fR then takes each configuration setting in
\fIfilename.dist\fR, then searches
\fIfilename.bak\fR\&.  If it finds a
configuration setting that has an identical
"\fIname\fR" and
"\fIversion\fR", then the corresponding configuration
setting value is taken
from \fIfilename.bak\fR, replacing the default in
\fIfilename.dist\fR\&. After
all configuration settings in \fIfilename.dist\fR are
looked up (and
potentially replaced), what's left becomes the new
\fIfilename\fR\&.
.SH "THE END RESULT"
.PP
The above process is a logical description.  The actual technical
implementation is slightly different (for example,
\fIfilename\fR is not
backed up to \fIfilename.bak\fR until the new configuration
file has been
already created), but is logically equivalent to this process.  This process
carries a number of consequences that must be considered.
.PP
If a new application revision needs a new configuration setting, it will
get a new \fIname\fR and \fIversion\fR\&.  Since \fIfilename.dist\fR is used
as a starting point for the new configuration file, the new configuration file
will include the new configuration setting.  When a configuration setting is
removed, it will disappear from the new configuration file for the same exact
reason.
.SH "CONFIGURATION SETTING VERSION"
.PP
\fBsysconftool\fR looks at both \fIname\fR
and \fIversion\fR\&. A
configuration setting with the same \fIname\fR but
different \fIversion\fRs
are seen by \fBsysconftool\fR as completely different settings.
The
existence of \fIversion\fR allows a finer-grained control of configuration
upgrades, as described below.
.PP
\fBsysconftool\fR copies setting values with the same
\fIname\fR
and \fIversion\fR from the old configuration file to the
new configuration
file.  However, the associated descriptive comments are not copied, and are
taken from the new \fIfilename.dist\fR\&.  Therefore, if a new
version of the
configuration file contains an updated or an embellished description of a
particular setting, it will be included in the new configuration file, but the
existing configuration value will be preserved!  Generally, if a configuration
setting does not change its meaning or function, its
\fIname\fR and
\fIversion\fR should remain the same. Its comments can
be edited to fix a
typo, or revised in a more substantive fashion.
\fIName\fR and \fIversion\fR
should only be changed if there's a functional change in the configuration
setting.
.PP
What to do with \fIname\fR and
\fIversion\fR after a functional change
depends on the nature and the magnitude of the change.  The nature and the
magnitude of the change must be considered not only with respect to the most
recent revision of the application, but to all the previous revisions as well.
When in doubt, go based upon the largest change in magnitude, in order to
guarantee a functional default setting, from
\fIfilename.dist\fR, and leave
it up to a living being to manually figure it out.
.PP
If only the default value of a setting should be changed for new
application installation, but the existing installations can continue to use
the existing value of the setting, both the \fIname\fR and \fIversion\fR
should be left alone.  Existing configuration settings will be preserved, and
new installations will get the new default.  The descriptive comment of this
setting can be updated too (see above).
.PP
This should be done only as long as \fBALL\fR
previous values of this
configuration setting will ALWAYS be valid in the new application revision. If
some possible values of this configuration setting will no longer be valid,
\fIversion\fR should be changed.
\fBsysconftool\fR does not care how
\fIname\fR and \fIversion\fR are
formatted.  Both are opaque labels.  The
only requirements is for the label to be different.  The difference between
changing \fIversion\fR and changing both
\fIname\fR and \fIversion\fR is
this:
.PP
If there's an old configuration setting with the same
\fIname\fR but different
\fIversion\fR, \fBsysconftool\fR will
still use the new,
safe, default value from \fIfilename.dist\fR, however
\fBsysconftool\fR will also append an additional comment,
on its own
accord, reminding the reader that this configuration value has been reset, and
the reader should consider whether to manually restore the configuration value
from the old configuration.
.SH "MISCELLANEA"
.PP
When \fBsysconftool\fR decides to keep an existing setting,
with the
same \fIname\fR and \fIvalue\fR,
it will also insert a short comment to that
effect, reminding the reader to check the default in
\fIfilename.dist\fR\&.
.SH "SEE ALSO"
.PP
\fBsysconftool\fR(1)\&.
