How do I increase the capacity of the Eclipse output console?

Open the Windows > Preferences menu.

Expand the Run/Debug > Console preferences.

Set the Console buffer size (characters) to something much bigger. 2147383647 / ~2GB is the upper limit (or 1000000 / ~1MB in older releases). Or just uncheck the Limit console output.

Under Window > Preferences, go to the Run/Debug > Console section, then you should see an option "Limit console output." You can uncheck this or change the number in the "Console buffer size (characters)" text box below.

(This is in Galileo, Helios CDT, Kepler, Juno, Luna, Mars, Neon, Oxygen and 2018-09)

Alternative

If your console is not empty, right click on the Console area > Preferences... > change the value for the Console buffer size (characters) (recommended) or uncheck the Limit console output (not recommended):

For CDT users / C/C++ build, also adjust the setting

in Window > Preferences

under C/C++ > Build > Console (!)

(This time in number of lines.)

This also affects the "CDT Global Build Console".