ruby-on-rails – 为什么我不能将站点地图写入具有只读文件系统

# In sitemap.rb

# Set the host name for URL creation
SitemapGenerator::Sitemap.default_host = "http://mycoolapp.com/"

# pick a place safe to write the files
#SitemapGenerator::Sitemap.public_path = 'tmp/'

# store on S3 using Fog
SitemapGenerator::Sitemap.adapter = SitemapGenerator::S3Adapter.new

# inform the map cross-linking where to find the other maps
SitemapGenerator::Sitemap.sitemaps_host = "http://#{ENV['FOG_DIRECTORY']}.s3.amazonaws.com/"

# pick a namespace within your bucket to organize your maps
SitemapGenerator::Sitemap.sitemaps_path = '/'

SitemapGenerator::Sitemap.create do
  # Put links creation logic here.
  #

  add '/home'

  add '/about'

  add '/contact'
end

每当我运行heroku运行rake sitemap：create我收到以下错误…

In '/app/tmp/':
511
rake aborted!
Read-only file system - /sitemap.xml.gz

我真的不知道为什么它不起作用.我甚至通过运行Rails.root.join(‘tmp’)作为初始化程序来确保创建tmp文件夹.任何帮助解决这个问题将不胜感激.