config - OpenSSL CONF library configuration files
The OpenSSL CONF library can be used to read configuration
files. It is used for the OpenSSL master configuration
file openssl.cnf and in a few other places like SPKAC
files and certificate extension files for the x509 utility.
A configuration file is divided into a number of sections.
Each section starts with a line [section_name] and ends
when a new section is started or end of file is reached. A
section name can consist of alphanumeric characters and
underscores.
The first section of a configuration file is special and
is referred to as the default section. This is usually
unnamed and is from the start of file until the first
named section. When a name is being looked up it is first
looked up in a named section (if any) and then the default
section.
The environment is mapped onto a section called ENV.
Comments can be included by preceding them with the #
character
Each section in a configuration file consists of a number
of name and value pairs of the form name=value
The name string can contain any alphanumeric characters as
well as a few punctuation symbols such as , ; and _.
The value string consists of the string following the =
character until end of line with any leading and trailing
white space removed.
The value string undergoes variable expansion. This can be
done by including the form $var or ${var}: this will substitute
the value of the named variable in the current
section. It is also possible to substitute a value from
another section using the syntax $section::name or ${section::name}.
By using the form $ENV::name environment
variables can be substituted. It is also possible to
assign values to environment variables by using the name
ENV::name, this will work if the program looks up environment
variables using the CONF library instead of calling
getenv() directly.
It is possible to escape certain characters by using any
kind of quote or the \ character. By making the last character
of a line a \ a value string can be spread across
multiple lines. In addition the sequences \n, \r, \b and
\t are recognized.
If a configuration file attempts to expand a variable that
doesn't exist then an error is flagged and the file will
not load. This can happen if an attempt is made to expand
an environment variable that doesn't exist. For example,
the default OpenSSL master configuration file used the
value of HOME which may not be defined on non Unix systems.
This can be worked around by including a default section
to provide a default value. Then, if the environment
lookup fails the default value will be used instead. For
this to work properly the default value must be defined
earlier in the configuration file than the expansion. See
the EXAMPLES section for an example of how to do this.
If the same variable exists in the same section then all
but the last value will be silently ignored. In certain
circumstances such as with DNs the same field may occur
multiple times. This is usually worked around by ignoring
any characters before an initial Two examples follow:
1.OU="My first OU"
2.OU="My Second OU"
Currently there is no way to include characters using the
octal \nnn form. Strings are all null terminated so nulls
cannot form part of the value.
The escaping isn't quite right. If you want to use
sequences such as \n you cannot use any quote escaping on
the same line.
Files are loaded in a single pass. This means that a variable
expansion will only work if the variables referenced
are defined earlier in the file.
This sample configuration file uses some of the features
mentioned:
# This is the default section.
HOME=/temp
RANDFILE= ${ENV::HOME}/.rnd
configdir=$ENV::HOME/config
[ section_one ]
# We are now in section one.
# Quotes permit leading and trailing whitespace
any = " any variable name "
other = A string that can \
cover several lines \
by including \\ characters
message = Hello World\n
[ section_two ]
greeting = $section_one::message
The following example shows how to expand environment
variables safely.
Suppose you want a variable called tmpfile to refer to a
temporary filename. The directory it is placed in can
determined by the the TEMP or TMP environment variables
but they may not be set to any value at all. If you
include the environment variable names and the variable
does not exist then this will cause an error when an
attempt is made to load the configuration file. By making
use of the default section both values can be looked up
with TEMP taking priority and /tmp used if neither is
defined:
TMP=/tmp
# The above value is used if TMP isn't in the environment
TEMP=$ENV::TMP
# The above value is used if TEMP isn't in the environment
tmpfile=${ENV::TEMP}/tmp.filename
Commands: x509(1), req(1), ca(1)
config(5)
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