If ldapsearch exits with an error, you’ll see a message like
this in the *Messages* buffer (all on one line):
ldap-search-internal: Failed ldapsearch invocation: ldapsearch "-Hldaps://ldap.gnu.org" "-bou=people,dc=gnu,dc=org" "-Dgnu\emacsuser" "-W" "-LL" "-tt" "(&(mail=name*))" "givenname" "sn" "mail"
The ldapsearch command is formatted such that it can be
copied and pasted into a terminal. Set the ldapsearch debug
level to 5 by appending -d 5 to the command line.