Bash script help on RPi

Question

I have a bash script that runs every hour. Output of this is sent to me via email. This is run through cronjob.

#!/bin/bash
# Script: temp_email.sh
# -------------------------------------------------------
cpu=$(</sys/class/thermal/thermal_zone0/temp)
echo "$(date) @ $(hostname)"
echo "-------------------------------------------"
echo "GPU => $(/opt/vc/bin/vcgencmd measure_temp)"
echo "CPU => $((cpu/1000))'C"
echo "-------------------------------------------"
echo ""
echo ""

As of now it provides temperatures via email. I wanted to add a loop and self-healing to mounted drives and http service.

I am using following commands to get results of apache2 service status

systemctl list-units --no-legend apache2.service | cut -d' ' -f4

The output if the service is running is "running". I want the loop to attempt to start the service if the status is anything but running. Output of this attempt.

I use the following to check status of external drives mounted to the Raspberry Pi.

 lsblk -dlno NAME,MOUNTPOINT /dev/sd??*

Again, I want to put this in a loop wheirein if the drive is unmounted it will first gracefully stop the apache2 service, mount the drive and later start the apache2 service.

I am unable to get "if & then statements" correctly. I do not want any changes in case both the service and drives are running as they should.

Thank you.

Answer 1

As I don't know how the output from systemctl command should be, I just will give you the steps I would follow:

• Don't use a loop. Use cron to execute your script periodically.
• Process the output of systemctl with grep for searching for a pattern of interest indicating mount status, and store this response.
• Process your response using an if to execute lsblk if needed

It would be something like this:

# script.sh
apache_running=1
systemctl status apache2.service | grep "running" || apache_running=0
if [ $apache_running -eq 0 ]
then
 echo "Apache is not running"
 lsblk -dlno NAME,MOUNTPOINT /dev/sd??*
else
 echo "Apache is running"
fi

Then, you add your script.sh file as an entry to the crontab

• Parth Maniar: Thank you and just a quick response that I do use cronjob for the script. Thank you.
• Parth Maniar: I am not sure how will work. I see only one If statement and there should be two (according to me) -- One for apache status and one for the mounted drives both having their actions.
• gustavovelascoh: In that case, you will have to check 2 conditions (with an AND operator), one for apache status and another for device status. If you have a list of devices to check, you can iterate through them in a for, I guess. It would be helpful If you provide an example output for each case.
• gustavovelascoh: I updated the answer for Apache service checking. But, what is the output of lsblk and how you identify the device to re-mount?

Answer 2

Instead of parsing the output of systemctl list-units, use systemctl is-active, and you can do things like this:

#!/bin/sh
# Mount point names in systemd unit style, with initial slash omitted and the
# rest replaced by dashes:
MOUNTPOINTS="MOUNT-POINT1 MOUNT-POINT2"
FAILED=0
for mountpoint in $MOUNTPOINTS
do
 if ! systemctl -q is-active $mountpoint.mount
 then
 echo "$mountpoint.mount is not active."
 if systemctl -q is-active apache2.service
 then
 echo "Stopping Apache first..."
 systemctl stop apache2.service
 fi
 echo "Trying to fix $mountpoint.mount..."
 systemctl start $mountpoint.mount || FAILED=1
 fi
done
if [ $FAILED -ne 0 ]
then
 echo "A mountpoint was down and we failed to fix it. Panic!" >&2
 exit 69 # EX_UNAVAILABLE
fi
if ! systemctl -q is-active apache2.service
then
 echo "apache2 service is not active. Attempting to start."
 systemctl start apache2.service
fi

• Parth Maniar: Thank you very much for the answer. Could you please try and help with the output of Apache2 at the end? As in, is there a way to find out if the apache restart worked or not?

Answer 3

An alternative to trying to do this yourself in a shell script might be to install and configure Monit to do it for you: https://mmonit.com/monit/