SMS Watchdog

My mobile carrier offers access to an API that can send SMS to its users. With systemd’s timers, I have been able to make a script that warns me when the load on my server is too high!
Basically, timers work by stating a service repeatedly; which in turn starts a script in this case.
This shell script is responsible for checking the load and sending a SMS. Of course, you can have it send you a mail too. Or tweet it, or whatever - sky’s the limit.

The script

This shell script is in charge of checking the load average and sending a SMS if it’s too high.

It is easy to get the load average of the last 5 minutes with the command cat /proc/loadavg | awk '{print $2}', but we must adjust the trigger depending on the amount on cores on the computer. To do so, nproc works fine, or more portable: grep processor /proc/cpuinfo -c (checks the amount of occurrence of the word “processor” in /proc/cpuinfo and thus the amount of cores).

Eventually we compare the load and the trigger limit. There’s a pitfall though: the shell (bash and sh as far as I know, I’ve heard it’s different for zsh) does not work on floating point number, so we need to pipe this computation to bc.

Here’s the script I come up with:

limit=125 # Percentage of total load

core_nbr=$(grep processor /proc/cpuinfo -c) # Amount of core. Equivalent to $(nproc) but more portable
trigger=$(echo "($limit / 100) * $core_nbr" | bc -l) # trigger limit, which depends of how many cores you have
load=$(cat /proc/loadavg | awk '{print $1}') # Load average of the last minute

if [ $(echo "$load > $trigger" | bc) = "1" ]; then
    echo "The load average is very great, I should send you an e-mail"
    message="There is something wrong with your server. The load average is $load.%0D%0AAs a reminder, the trigger limit is $trigger." # %0D%0A is a line break

    curl "$message"


/etc/systemd/system/ is the directory where every manually added systemd file should go, so this is where you can create a service file called for example getkey-sms-watchdog.service.

Description=Send a SMS if the load average is TOO DAMN HIGH


# It's of no use making HTTP requests when there's no Internet access

Now, the timer. It must have the same filename as the service file, except of course the extension which must be “.timer”. So, let’s create getkey-sms-watchdog.timer:

Description=Send a SMS if the load average is TOO DAMN HIGH

OnBootSec=10min # Start first 10 minutes after boot
OnUnitActiveSec=5min # Then restart every 5 minutes


You can enable all of this by running:

sudo systemctl enable getkey-sms-watchdog.timer # Start on boot
sudo systemctl start getkey-sms-watchdog.timer # Enable it for this session, too

It is possible to check that the timer is working properly by running systemctl list-timers.

And here is a pic of the result!
sms conversation screenshot

Tags: systemd