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Raspberry pie is a low-cost computer, so one of its application scenarios is to act as a small server. I usually connect to a raspberry pie on my local area network and do some data backup and upload. At such times, we want to reduce the direct operation of raspberry pie, so we can use some mission planning methods to make raspberry pie automate the task.

Shutdown

Reboot

Sleep 10

Planning tasks with cron

Cron is a commonly used task planning software in UNIX system. You can ask the system to perform specific tasks at a specific time in cron. Cron has a running daemon in the system. When the system time matches a certain planning record, the daemon starts the corresponding task. Run the following command in the raspberry pie application line to find the daemon for cron:

Ps aux | grep cron

The results are as follows:

Root 424 0.0 0.2 5072 2384? Ss 14:40 0:00 / usr/sbin/cron-fpi 6938 0.00.2 4280 2008 pts/1 S + 17:42 0:00 grep-- color=auto cron

The first item in the record is the process of cron.

If you want to plan a task, you can edit the planning record with the following command:

Crontab-e

In the planning record, there is one record for each action, and # begins with comments. Each row of records is divided into six columns, separated by spaces, indicating minutes (mjournal 0-59), hours (hjournal 0-23), which day of the month (dom,1-31), month (mon,1-12), which day of the week (dow,0-6), and the command to be executed. When filling in the planned time, in addition to using numbers, you can also use * to indicate all:

# m h dom mon dow command 30 5 10 3 * touch / tmp/test.log

It says that touch / tmp/test.log will be executed at 05:30 on March 10th every year.

# m h dom mon dow command 10 18 * echo "Hello World" > / home/pi/log

Execute echo "Hello World" > / home/pi/log at 18:10 every day.

In a column, you can also plan multiple time steps, such as:

# m h dom mon dow command 10 2-4 * echo "Hello World" > / home/pi/log

It is executed at 2:10, 3:10 and 4:10 every day. In other words, "Nmurm M" represents the range from N to M.

# m h dom mon dow command 30 1 echo 5 * echo "Hello World" > / home/pi/log

It is executed at 1:30 and 5:30 every day. In other words, "NMague M" represents N and M in time.

After the planning record crontab is saved, cron will execute the corresponding command at the corresponding time according to the plan. Each user has its own crontab, and when the cron wants to execute the plan, it will also execute it as the corresponding user. If I modify the saved crontab,cron as a pi user, I will run each command as pi. If you want to modify another user's crontab, you can use the-u keyword:

Sudo crontab-e-u root uses cron to boot

In addition to timing, cron can also be used to boot. By adding the following line of record to crontab, you can easily implement it:

@ reboot touch / home/pi/reboot.log uses / etc/init.d to realize boot

There are many scripts under the / etc/init.d folder under the raspberry pie, such as the cron we already know. This cron script wraps the cron daemon as a service, defining its specific behavior when it starts, restarts, and terminates. In this way, users do not need to make too complex settings when enabling the corresponding services. When the service is terminated, the operating system can also automatically reclaim related resources according to the definition of the script. Users can also set important services to boot, saving the trouble of starting manually. Therefore, we see a lot of services working silently in / etc/init.d, such as ssh, bluetooth, rsync, and so on.

Service scripts follow a specific format. Such as the / etc/init.d/test script below:

#! / bin/sh# Start/stop the test daemon.#### BEGIN INIT INFO# Provides: test# Required-Start: $remote_fs $syslog $time# Required-Stop: $remote_fs $syslog $time# Default-Start: 2 34 "Default-Stop: 0 1" Short-Description: test# Description: test### END INIT INFOdo_start () {echo "start"} do_stop () {echo "stop "} do_restart () {echo" restart "} do_status () {echo" status "} do_fallback () {echo" fallback "} case" $1 "instart) do_start ; stop) do_stop;; restart) do_restart;; status) do_status;; *) do_fallback;; esacexit 0

The script begins with a header message. In addition to the basic introduction, there is other information in the header information. Required-Start describes other applications that the system must start before the test application starts. The applications listed by Required-Stop must end after the end of the test application. The default run level described in Default-Start and Default-Stop. Unix systems can work in different operating modes, such as single-user mode and multi-user mode, each of which is called a run level. Most UNIX systems follow:

Run level: 0 shutdown, shutdown 1 single user, no network connection, do not run daemon process, do not allow non-superuser login 2 multi-user, no network connection, do not run daemon 3 multi-user, normal startup system 4 user customization 5 multi-user, restart with graphical interface 6

In test scripts, the default supported run levels are 2, 3, 4, and 5.

A case branch structure is included in the main program of the script, which explains the actions that the application should take when entering the state of start, stop, restart, and status. We can manually change the state of the script with the service command:

Sudo service test start

The corresponding action in the script is called.

/ etc/init.d/myscript cannot be started at random yet. When Linux starts up, what it really checks is the / etc/rcN.d folder and executes the script in it. The N here represents the run level. For example, when running level 2, Linux checks the / etc/rc2.d folder and executes the script. We need to copy the services in / etc/init.d or establish a soft connection to / etc/rcN.d in order for the service to boot at that runlevel. However, we can use the update-rc.d command to do this more easily:

Sudo update-rc.d cron defaults # establish soft links according to the default supported run level sudo update-rc.d cron remove # remove soft links to avoid using / etc/rc.local

The raspberry pie website provides a way to modify / etc/rc.local to perform user-defined tasks when the raspberry pie is turned on. For example, execute the date command in this file:

#! / bin/sh-eBay # rc.local## This script is executed at the end of each multiuser runlevel.# Make sure that the script will "exit 0" on success or any other# value on error.## In order to enable or disable this script just change the execution# bits.## By default this script does nothing.# timedate > / tmp/rc.local.logexit 0

However, this startup method is not recommended. / etc/rc.local is a script executed at the end of system initialization. If you add too many tasks to this script, it will not only slow down the boot, but also cause administrative confusion. Therefore, / etc/rc.local is often only used to modify some parameters that need to be set during the startup process, and does not involve specific task startup. If you want to start some services with boot, you should avoid using / etc/rc.local.

Summary

This chapter mainly introduces the task planning of raspberry pie with cron and the startup program in a variety of ways.

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