If you have .db files on a Linux system, they may be Berkeley DB (BDB) database files. Berkeley DB originated at the University of California, Berkeley as part of BSD, Berkeley's version of the Unix operating system. The initial release was in 1994. Berkely DB was futher developed by SleepyCat Software from 1996 to 2006. In February 2006, Oracle Corporation acquired SleepyCat and continued development of the software.
You can ascertain if a .db file is a BDB file using
the file command.
E.g., the
Sendmail email software uses .db files stored in /etc/mail
to control various aspects of the software's functionality. For instance,
you can specify the domains for which Sendmail will accept email in
the /etc/mail/local-host-names file or create "virtual users"
using the /etc/mail/virtusertable file. But to alter
Sendmail's behavior using these files, you need to generate .db files from
the text files using the
makemap command. E.g., makemap hash
/etc/mail/virtusertable < /etc/mail/virtusertable. If you check
the type of file for the .db file that will be created by the
makemap utility with the file command, you will
see the following information, if you check from the root account:
# file /etc/mail/virtusertable.db /etc/mail/virtusertable.db: Berkeley DB (Hash, version 9, native byte-order) #
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