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ISBN : 978-2-7460-9712-4
EAN : 9782746097124
(Editions ENI)


CentOS 2.1AS







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 . e.g.

 1.OU="My first OU"
 2.OU="My Second OU"


Here is a sample configuration file using some of the features mentioned above.

 # This is the default section.
 [ 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

This next 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 just include the environment variable names and the variable doesn’t 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:

 # The above value is used if TMP isn’t in the environment
 # The above value is used if TEMP isn’t in the environment


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 like \n you can’t use any quote escaping on the same line.

Files are loaded in a single pass. This means that an variable expansion will only work if the variables referenced are defined earlier in the file.


x509(1), req(1), ca(1)