昨天想要为每日一图脚本添加定时运行时才发现，貌似crond不工作了。
于是发现原来的dcron早就被踢进AUR了，现在的crond是cronie童鞋。。可是要肿么用呢？

发现Archlinux论坛上也有人有这样的疑问，思路整理如下：

目前，可以使用crontab -e来添加命令或者把想定时运行的命令放在相应的cron.{hourly,daily,monthly,weekly}文件夹中。两者的区别是，通过crontab -e添加的任务可以指定具体的运行时间，可以精确到分钟，但需要保证机器一直运行，若在指定的时间点计算机没有在线，那么任务就不会运行；而放在那几个文件夹的脚本不可以指定精确的运行时间，但不要求计算机一直在线，计算机一旦在线就会检查相应文件夹下的脚本是否应该执行，若符合执行的条件则执行。那么它是通过什么方法来检查的呢？配置文件/etc/anacrontab的一个字段period in days指定了某个文件夹下的脚本的运行间隔时间，若计算机看到某个脚本距上次执行时间已经有n天或大于n天，那么它就会运行这个脚本。
以下的专业解释来自Man，哈哈

Anacron is used to execute commands periodically, with a frequency specified in days. Unlike cron(8),it does not assume that the machine is running continuously. Hence, it can be used on machines that are not running 24 hours a day to control regular jobs as daily, weekly, and monthly jobs.

Anacron reads a list of jobs from the /etc/anacrontab configuration file (see anacrontab(5)). This file contains the list of jobs that Anacron controls. Each job entry specifies a period in days, a delay in minutes, a unique job identifier, and a shell command.

For each job, Anacron checks whether this job has been executed in the last n days, where n is the time period specified for that job. If a job has not been executed in n days or more, Anacron runs the job’s shell command, after waiting for the number of minutes specified as the delay parameter.

After the command exits, Anacron records the date (excludes the hour) in a special timestamp file for that job, so it knows when to execute that job again.

To summerize then,if you want to execute a script at a particular time, you should use crontab -e.If you just want the script to execute regardless of the time, you should drop it in the appropriate folder.

做完上面这些后，我悲催的发现crond其实不适合用于定时运行每日一图的脚本。。最后加在awesome的开机启动，通过theme.wallpaper参数可以来设置墙纸，不过有一个矛盾，只能先设置墙纸然后才能下载每日一图。。暂时没找到很好的可以先下载再设置的方法。所以，目前用不了当天的图，用的是前一天的图。。