I'm running Ubuntu 16.04.6 LTS with all updates installed.
Currently I see strange behavior: I can't start new GTK applications and Qt ones.
For GTK-based applications I get:
$ atril file.pdf Failed to get bus connection: GDBus.Error:org.freedesktop.DBus.Error.LimitsExceeded: Failed to determine seats of user "1000": Too many open files
For Qt-based applications I get:
$ konsole QDBusConnection: session D-Bus connection created before QCoreApplication. Application may misbehave. KUniqueApplication: Cannot find the D-Bus session server: "Failed to determine seats of user \"1000\": Too many open files" KUniqueApplication: Pipe closed unexpectedly.
I cant guess why this happens.