如何让whenever gem在我的Rails习惯追踪应用中正常工作？

我正在开发一款「习惯追踪」应用，需要每天自动创建Day模型实例。尝试用whenever gem部署定时任务，但无论设置分钟/小时/天周期，都无法生成新实例。已多次跟随教程操作、重新部署，均无效果。

相关代码 #

schedule.rb #

every 3.minute do
  command "cd /Users/myusername/code/myusername/habit-tracker && bundle exec rails runner 'Day.create!'"
end

set :environment, "development"


# every 1.minute do
#   command "bundle exec rails runner Day.create!"
#   rake 'batch:create_day', environment: "development"
#   runner 'Day.create!', environment: "development"
# end

# every :minute do
#   command "bundle exec rails runner Day.create!"
#   rake 'batch:create_day', environment: "development"
#   runner 'Day.create!', environment: "development"
# end

batch.rake #

namespace :batch do
  desc "Create a new instance of Day everyday"
  task create_day: :environment do
    Day.create!
  end
end

crontab -l 输出 #

# Begin Whenever generated tasks for: /Users/myusername/code/myusername/habit-tracker/config/schedule.rb at: 2024-04-30 17:17:19 +0200
0,3,6,9,12,15,18,21,24,27,30,33,36,39,42,45,48,51,54,57 * * * * /bin/bash -l -c 'cd /Users/myusername/code/myusername/habit-tracker && bundle exec rails runner \'\'Day.create!\'\''

# End Whenever generated tasks for: /Users/myusername/code/myusername/habit-tracker/config/schedule.rb at: 2024-04-30 17:17:19 +0200

补充说明 #

• 无任何报错信息，每次更新schedule文件后都执行whenever --update-crontab和bundle exec whenever，得到如下输出：

* * * * * /bin/bash -l -c 'cd /Users/myusername/code/myusername/habit-tracker && bundle exec rails runner \'\'Day.create!\'\' >> log/cron_error.log 2>&1'

## [message] Above is your schedule file converted to cron syntax; your crontab file was not updated.
## [message] Run `whenever --help' for more options.

• 使用macOS系统，无法执行sudo service cron status命令，求替代排查方法。

排查与解决步骤 #

1. 检查macOS上cron服务状态 #

macOS用launchctl管理服务，替代service cron status的命令：

• 查看cron是否运行：launchctl list | grep cron，输出中包含com.vix.cron且PID不为0，说明服务正常运行
• 或者用pgrep cron，有数字输出表示cron进程存在
• 若未运行，启动cron：sudo launchctl start com.vix.cron

2. 查看cron执行日志 #

macOS默认cron日志路径为/var/log/cron，实时查看日志：

tail -f /var/log/cron

也可以在定时任务中添加自定义日志输出，修改schedule.rb：

every 3.minute do
  command "cd /Users/myusername/code/myusername/habit-tracker && bundle exec rails runner 'Day.create!' >> log/cron_output.log 2>&1"
end

之后查看log/cron_output.log获取具体执行错误信息。

3. 修复whenever命令转义问题 #

从crontab输出可见，命令中的引号被错误转义为\'\'Day.create!\'\'，导致rails runner执行失败。建议改用whenever内置的runner方法，自动处理引号：

every 3.minute do
  runner 'Day.create!', environment: 'development'
end
set :environment, 'development'

重新更新crontab：

whenever --update-crontab --set environment=development

4. 手动验证任务可行性 #

直接在终端执行任务命令，排查代码或环境问题：

• 测试rails runner命令：

cd /Users/myusername/code/myusername/habit-tracker && bundle exec rails runner 'Day.create!'

• 测试rake任务：

bundle exec rake batch:create_day

若执行失败，会直接输出错误信息，定位问题（比如Day模型验证失败、数据库连接问题等）。

5. 解决cron环境变量缺失问题 #

cron的环境变量与终端用户环境不同，可能找不到ruby或bundle。先获取完整路径：

which ruby
which bundle

修改schedule.rb中的command，使用完整路径：

every 3.minute do
  command "cd /Users/myusername/code/myusername/habit-tracker && /path/to/bundle exec /path/to/ruby bin/rails runner 'Day.create!' >> log/cron_error.log 2>&1"
end

替换/path/to/bundle和/path/to/ruby为实际输出路径。

内容的提问来源于stack exchange，提问作者Camille H