makemap

makemap is a command-line utility used in Unix-like operating systems for creating map files. Map files are essential for certain programs that need to associate symbolic names with numerical identifiers or other data. For example, makemap is often used in conjunction with the sendmail Mail Transfer Agent (MTA) to create mapping databases for features like virtual domains, mail aliases, or access control lists.

The basic function of makemap is to read a text-based input file and convert it into a more efficient, often binary, format that can be quickly accessed by applications. The input file typically consists of pairs of keys and values, where each pair is on a new line. The separator between the key and value can vary, but a common separator is whitespace.

When makemap is executed, it takes the input file as an argument and specifies the type of map file to be created. Common map file types include hash, btree, and skip list, each offering different performance characteristics for lookup operations. The generated output file is then placed in a designated location, ready for use by the application that requires it. Understanding makemap is therefore important for system administrators managing mail servers or other services that rely on these mapping mechanisms for efficient data retrieval and configuration.