On November 23 syl20bnr added a new toggle called
spacemacs/toggle-truncate-lines, available on SPC t l. Another toggle you may also find useful is
spacemacs/toggle-visual-line-navigation, available on SPC t L. See Github commit.
This is how your
dotspacemacs/user-config can look like to enable both toggles:
(defun dotspacemacs/user-config ()
"Configuration function for user code.
This function is called at the very end of Spacemacs initialization after
layers configuration. You are free to put any user code."
;; Visual line navigation for textual modes
(add-hook 'text-mode-hook 'spacemacs/toggle-visual-line-navigation-on)
If you don't know where
dotspacemacs/user-config is, it's in your
.spacemacs file, available by pressing SPC f e d.
The hook for
spacemacs/toggle-visual-line-navigation-on is because it doesn't work globally otherwise.
M-x auto-fill-mode(which will toggle it on and off) and, if that works and is what you mean, you can disable it automatically in your init file.
truncate-linesafter starting Spacemacs. This will tell you what it is set to when starting up.