How to log a cronjob?

Question

I have this Main script:

#!/bin/bash

#Array of Mac hostnames separated by spaces
my_macs=( Mac111 Mac121 Mac122 Mac123 Mac124 Mac125 Mac126 Mac127 Mac128 Mac129 )

#Steps through each hostname and issues SSH command to that host
#Loops through the elements of the Array

for n in "${my_macs[@]}"
do
    # -q quiet
    # -c nb of pings to perform

    ping -q -c3 "${n}" > /dev/null

    if [ $? -eq 0 ]
    then
        ssh admusr@"${n}" 'sudo bash -s' < ./documents/ShutdownUPTIME.sh
    else
        echo "${n} is not available"
    fi

done

exit 0

The main script runs a seperate script. This is ShutdownUPTIME.sh:

#!/bin/bash
BOOT_TIME=$(sysctl -n kern.boottime | sed -e 's/.* sec = \([0-9]*\).*/\1/')
CURR_TIME=$(date +%s)
MAX_UPDAYS=1 #Days

DAYS_UP=$(( ( $CURR_TIME - $BOOT_TIME) / 86400 ))
if [ $DAYS_UP -ge ${MAX_UPDAYS} ];then
    echo Mac is going to shutdown 
    sudo shutdown -h now
else
        echo No shutdown for Mac needed
fi

Now I have 2 problems:

First problem:

I made a cronjob (with crontab -e: 30 23 * * * ./documents/shutdownsimple.sh). I want to log this cronjob, either through the script or the cronjob itself (I want to know when it runs and what exactly it does; for more information look at the echo in the scripts), how can I do that?

Second problem:

If I log the script it will just say Mac is going to shutdown but I want it to say Mac111 is going to shutdown or No need to shutdown Mac125. The names do not show though, any idea how I can accomplish that?

If you find any mistakes, feel free to edit my post, english is not my first language

Answer 1

Firstly to get the script to show the name of the machine two things:
a) Change the way you remotely execute the script to run it directly on the remote host. This requires that you copy the script to the remote machine. I like to store my personal utility scripts in a directory called "do" in my home directory, so I would have it as
~/do/ShutdownUPTIME.sh

Now change the line which reads
ssh admusr@"${n}" 'sudo bash -s' < ./documents/ShutdownUPTIME.sh

to this:
ssh admusr@"${n}" sudo do/ShutdownUPTIME.sh $n

Basically you are passing $n, the name of the machine, to it as parameter.

b) Then change the ShutdownUPTIME.sh script to use the passed argument. Where you have Mac put $MACNAME. Near the start of the script add the line
MACNAME=$1

The script will now look like this:

#!/bin/bash
MACNAME=$1
BOOT_TIME=$(sysctl -n kern.boottime | sed -e 's/.* sec = \([0-9]*\).*/\1/')
CURR_TIME=$(date +%s)
MAX_UPDAYS=1 #Days

DAYS_UP=$(( ( $CURR_TIME - $BOOT_TIME) / 86400 ))
if [ $DAYS_UP -ge ${MAX_UPDAYS} ];then
    echo Notice: $MACNAME is going to shutdown 
    sudo shutdown -h now
else
        echo Info: No shutdown for $MACNAME needed
fi

I also added "Notice" and "Info" to the output commands to give them some level of importance - this helps with later log filtering.

For bonus make the script handle the situation where you did not supply a Mac Name by having a default value. For example the MACNAME value assignment becomes

MACNAME=${1:-$(hostname)}

About logging: Cron will send you an email with the output of every job, but this can be really inconvenient. The simplest solution is to redirect the output of the commands to a local log file.

For this simply add the redirection on the "done" line of the loop, so it becomes

done | tee -a $LOGFILE 2>&1

And this of course requires you to set up a name in the LOGFILE variable earlier in the script, so add a line like this near the start:
LOGFILE=/var/log/refreshing.log
(Note: Specify a path to a file which you have permission to write to)

In addition you may want to regularly add a timestamp to this log, so just before the loop add the line
echo Running Refresh at $(date) | tee -a $LOGILFE

Logging output from the cron command means your logging only happens when your script is executed from cron. Making the script manage it's own logging is therefore preferred. I changed the script to use tee in stead of redirection so that when you run it on the command line you can still see the output.