Load this then put "%default_mode tofile" in a cloud.sagemath worksheet.

tofile cell decorator

def tofile(s):
    maxout=500
    import uuid
    filename = str(uuid.uuid4()) +'.log'
    o = open(filename,'w')

    stdout = sys.stdout
    class Stdout:
        def __init__(self):
            self.t = 0
            self.extra_out = False
        def reset(self):
            stdout.reset()
        def write(self, s):
            if self.t < maxout:
                stdout.write(s[:maxout-self.t])
                self.t += min(len(s),maxout-self.t)
                if self.t >= maxout:
                    self.extra_out = True
                    stdout.write("...")
                    stdout.flush()
            else:
                self.extra_out = True
            o.write(s)
        def flush(self):
            o.flush()

    sys.stdout.flush()
    sys.stdout = Stdout()
    salvus.execute(s)
    extra_out = sys.stdout.extra_out
    sys.stdout = stdout
    o.close()
    if extra_out:
        url = salvus.file(filename, show=False)
        salvus.html("<a href='%s' target='_blank' class='pull-right btn btn-info'>more output...</a></b>"%url)
    os.unlink(filename)
    salvus.stdout('',done=True)