Search notes:

/var/lib/dpkg

/var/lib/dpkg contains the dpgk database.
The dpkg database can be queried with dpkg-query.
Files and directories I've found in /var/lib/dpkg include:
alternatives/
available
cmethopt
diversions
diversions-old
info/
lock
lock-frontend
parts/
statoverride
statoverride-old
status
status-old
triggers/
updates/

See also

dpkg and its --admindir options which alows to use another directory.
/var/lib

Index

Fatal error: Uncaught PDOException: SQLSTATE[HY000]: General error: 8 attempt to write a readonly database in /home/httpd/vhosts/renenyffenegger.ch/php/web-request-database.php:78 Stack trace: #0 /home/httpd/vhosts/renenyffenegger.ch/php/web-request-database.php(78): PDOStatement->execute(Array) #1 /home/httpd/vhosts/renenyffenegger.ch/php/web-request-database.php(30): insert_webrequest_('/notes/Linux/fh...', 1788375401, '216.73.217.21', 'Mozilla/5.0 App...', NULL) #2 /home/httpd/vhosts/renenyffenegger.ch/httpsdocs/notes/Linux/fhs/var/lib/dpkg/index(64): insert_webrequest() #3 {main} thrown in /home/httpd/vhosts/renenyffenegger.ch/php/web-request-database.php on line 78