使用注意:

$ watch --interval .30 script_to_run_every_30_sec.sh

Have a look at frequent-cron - it's old but very stable and you can step down to micro-seconds. At this point in time, the only thing that I would say against it is that I'm still trying to work out how to install it outside of init.d but as a native systemd service, but certainly up to Ubuntu 18 it's running just fine still using init.d (distance may vary on latter versions). It has the added advantage (?) of ensuring that it won't spawn another instance of the PHP script unless a prior one has completed, which reduces potential memory leakage issues.

不需要两个cron条目，你可以把它放在一个:

* * * * * /bin/bash -l -c "/path/to/executable; sleep 30 ; /path/to/executable"

在你的例子中:

* * * * * /bin/bash -l -c "cd /srv/last_song/releases/20120308133159 && script/rails runner -e production '\ "insert_latest \”;睡眠30分钟;cd /srv/last_song/releases/20120308133159 && script/rails runner -e production '\ " Song.insert_latest'\ " "

使用注意:

$ watch --interval .30 script_to_run_every_30_sec.sh

我刚刚有一个类似的任务要做，并使用了以下方法:

nohup watch -n30 "kill -3 NODE_PID" &

我需要在几个小时内每30秒执行一次定期kill -3(以获得程序的堆栈跟踪)。

nohup ... & 

这是在这里确保我不会失去手表的执行，如果我松散的外壳(网络问题，windows崩溃等…)

Cron作业不能用于以秒为间隔调度作业。例如，你不能安排一个cron作业每5秒运行一次。另一种方法是编写一个使用sleep 5命令的shell脚本。

使用bash while循环每5秒创建一个shell脚本。sh，如下所示。

$ cat every-5-seconds.sh
#!/bin/bash
while true
do
 /home/ramesh/backup.sh
 sleep 5
done

现在，在后台使用nohup执行这个shell脚本，如下所示。这将在退出会话后继续执行脚本。这将每5秒执行一次backup.sh shell脚本。

$ nohup ./every-5-seconds.sh &