When running drush cc all I got "cache-clear all` is deprecated for Drupal 8 and later" although it's a D7 installation. Running drush without parameters gave me the hint that the "Drupal root was not found". It looks like Drush 9 is not really compatible anymore with D7. Downgrading to Drush 8 helped:
composer global remove drush/drush composer global require drush/drush:8.1.10
This problem drove me nuts. The PHP code running PDO SQL queries ran fine on an old server, but threw this PDO Exception on the newly installed one. The solution included:
After importing a view with the name "Event", deleting it, and reimporting it with the name "event" cache clear did not work anymore: "PDOException: SQLSTATE[23000]: Integrity constraint violation: 1062 Duplicate entry 'adminimal-views-events-block_1' for key 'tmd'". The problem was in the block table. It contained blocks of the form "Events-block_1", which were not deleted together with the view. Removing the orphaned entries manually and re-running cc solved the problem. The correct delta entries of the form "events-block_1" get inserted.
When reading a dump this error can occur due to very long lines. It can be worked around by setting max_allowed_packet to a higher value in /etc/mysql/mysql.conf.d/mysqld.cnf, for example, 64M.
I tried to compile a C++ program that was pimped by using the gflags and glog libraries. I installed them by apt-get install libgflags-dev libgoogle-glog-dev. When linking the executable, I got undefined reference errors like
mssj.o: In Funktion `main': mssj.cpp:(.text.startup+0x131): Nicht definierter Verweis auf `google::InitGoogleLogging(char const*)' mssj.cpp:(.text.startup+0x145): Nicht definierter Verweis auf `google::ParseCommandLineFlags(int*, char***, bool)' mssj.cpp:(.text.startup+0x346): Nicht definierter Verweis auf `google::LogMessageFatal::LogMessageFatal(char const*, int)' mssj.cpp:(.text.startup+0x34e): Nicht definierter Verweis auf `google::LogMessage::stream()' mssj.cpp:(.text.startup+0x356): Nicht definierter Verweis auf `google::LogMessageFatal::~LogMessageFatal()' mssj.cpp:(.text.startup+0x476): Nicht definierter Verweis auf `google::LogMessageFatal::LogMessageFatal(char const*, int)' mssj.cpp:(.text.startup+0x480): Nicht definierter Verweis auf `google::LogMessage::stream()' mssj.cpp:(.text.startup+0x48a): Nicht definierter Verweis auf `google::LogMessageFatal::~LogMessageFatal()' mssj.o: In Funktion `_GLOBAL__sub_I__ZN3fLS16FLAGS_input_fileB5cxx11E': mssj.cpp:(.text.startup+0xd8c): Nicht definierter Verweis auf `google::FlagRegisterer::FlagRegisterer(char const*, char const*, char const*, char const*, void*, void*)' mssj.cpp:(.text.startup+0xdc7): Nicht definierter Verweis auf `google::FlagRegisterer::FlagRegisterer(char const*, char const*, char const*, char const*, void*, void*)' mssj.cpp:(.text.startup+0xe37): Nicht definierter Verweis auf `google::FlagRegisterer::FlagRegisterer(char const*, char const*, char const*, char const*, void*, void*)' mssj.cpp:(.text.startup+0xe72): Nicht definierter Verweis auf `google::FlagRegisterer::FlagRegisterer(char const*, char const*, char const*, char const*, void*, void*)' mssj.cpp:(.text.startup+0xe9f): Nicht definierter Verweis auf `google::FlagRegisterer::FlagRegisterer(char const*, char const*, char const*, char const*, void*, void*)' collect2: error: ld returned 1 exit status
The issue was the call of the linker. It expects shared library files to appear AFTER the executable using them, so instead of g++ -lgflags -lglog MANY.o-FILES -o EXECUTABLE it wants the libraries at the end. g++ MANY.o-FILES -o EXECUTABLE -lgflags -lglog solved the problem.