在stackoverflow中找到了终极解决办法：
>>> import matplotlib >>> matplotlib.matplotlib_fname() # This is the file location in Ubuntu ‘/etc/matplotlibrc‘
找到matplotlibrc之后，将backend从tkAGG修改为AGG
http://stackoverflow.com/questions/2801882/generating-a-png-with-matplotlib-when-display-is-undefined
pylab绘图no display name and no $DISPLAY environment variable的解决办法
原文：http://www.cnblogs.com/yumtaoist/p/4249840.html