Bash脚本无限循环关闭

Question

I wrote a short bash script which collects CPU temperature every 10 seconds and outputs it to a file along with some other data. Running the script in the terminal works perfectly fine. However, once I setup the script to run on startup, I encounter 2 problems:

-opening the resulting .txt file with gedit results in: "gedit has not been able to detect the character encoding. Please check that you are not trying to open a binary file." Select a character encoding from the menu and try again." Opening the file with Libre Writer works fine and the file has correct data.

-first time when I try to shutdown after placing the script in /etc/init.d/ and running update-rc.d the PC takes inexplicably long to do it, to the point that I have to shutdown manually.

This is the script code:

#!/bin/bash

readonly DIR_PATH='/home/ivan/Documents/temp_data/' # path to output dir, change to yours, don't use HOME variable

while true; do
    temps_str=$(sensors | grep "Physical" | tr -dc "[:digit:][^ °.C]") #  extract numbers from sensors command output
    temps_str=${temps_str:5} # remove first 5 characters, they are ' ', ' ', '0', ' ', ' ' and useless
    temps_array=($temps_str) # convert string to array

    temp_now=${temps_array[0]} # CPU temp now
    temp_high=${temps_array[1]} # highest CPU temp recorded in this session
    temp_max=${temps_array[2]} # CPU temp at which PC turns off

    dt=$(date +%d-%m-%Y) # date, format: dd-mm-yyyy
    time=$(date +%H:%M:%S) # time, format: HH:MM:SS

    # create output directory if it doesn't already exist
    if [ ! -d $DIR_PATH ]; then
        mkdir -m 755 $DIR_PATH
    fi

    echo $time $temp_now $temp_high $temp_max >> ${DIR_PATH}${dt}.txt # write to output file

    sleep 10 # wait 10 seconds
done

This is the format of the output file:

17:22:21 58.0°C 87.0°C 105.0°C

17:22:31 56.0°C 87.0°C 105.0°C

17:22:41 58.0°C 87.0°C 105.0°C

17:22:51 59.0°C 87.0°C 105.0°C

17:23:01 58.0°C 87.0°C 105.0°C

17:23:11 59.0°C 87.0°C 105.0°C

17:23:21 60.0°C 87.0°C 105.0°C

17:23:32 63.0°C 87.0°C 105.0°C

17:23:42 63.0°C 87.0°C 105.0°C

When I get the 'eternal shutdown', I shut it down manually. After rebooting, the file shows that the scripts was still running and writing to file while the PC was frozen, then a line of #s (which probably get written during the manual shutdown). I'm wondering what causes the freeze and why does the .txt file charset get 'corrupted'?

Answer 1

The scripts in /etc/init.d are expected to start and stop services. So they need to be prepared to accept the command-line arguments start and stop . (If they also accept arguments like restart and status , that's a bonus.)

When you put a symlink to one of these scripts in a directory in /etc/rcN.d , then the script will be invoked with either the argument start or stop :

• On start-up, the argument depends on whether the name of the symlink starts with S ( start ) or K ( stop -- the letter stands for "kill").

• On shut-down, the argument will be stop .

(The above is the debian behaviour, taken from the Debian policy manual .)

Your script is not of this form. It simply runs the monitor program. So when it is invoked with the argument stop , it will not stop monitoring. It will just start up another monitoring loop, which never terminates . Because it is called directly from the shutdown sequence, that will prevent the shutdown from terminating.

The usual approach to writing init.d scripts is based on the following:

• When called with the start option, the script initiates the service (ie, your current monitoring script) as a daemon process and writes its PID to a file whose name is related to the service name. (A common place to put this file is the /var/run directory, usually with the extension .pid .) There are some standard utilities to start a process as a daemon, which can help with this task. If you have a Debian-based (including Ubuntu) installation, take a look at the shell utility library /lib/lsb/init-functions .

• When called with the stop option, the script uses the PID stored in the file created in the start action to kill the process. It then deletes the pid file.