Why Does My Cron Job Always Restart My Process? The Hidden PATH Pitfall

Problem Origin

The author wanted a program to auto‑restart after a crash, so they added a cron job that runs a monitoring script every minute to check if the video_checkup process is running and start it if not.

Problem Description

The script /home/watch.sh contains the following logic:

#!/bin/sh
shell_log_file=/home/start.log
pid_count=`pidof video_checkup | wc -w`
path=$(cd "$(dirname "$0")"; pwd)
run_command="${path}/video_checkup"
config_path="${path}/config.json"
if [ $pid_count -eq 0 ]; then
    echo `date +%Y-%m-%d_%H:%M:%S` " run $run_command $config_path" >> $shell_log_file
    $run_command $config_path
else
    echo `date +%Y-%m-%d_%H:%M:%S` " video_checkup already running" >> $shell_log_file
fi

The cron entry added with crontab -e is: * * * * * /home/watch.sh > /dev/null 2>&1 In practice the video_checkup process multiplied rapidly because the script thought the process was absent each minute.

Problem Analysis

Debugging showed that the condition if [ $pid_count -eq 0 ] was always true; $pid_count was always zero even though the process was running. Logging the environment variables revealed that the PATH inside cron was only /usr/bin:/bin, whereas an interactive shell had a much longer PATH that includes /sbin where the pidof binary resides ( /sbin/pidof).

Because pidof was not found in cron’s PATH, the command failed silently; the failure produced no output for wc -w, which then returned 0, making the script think no process existed.

Problem Solution

Adding the full PATH from the interactive shell to the script fixes the issue. Insert at the beginning of watch.sh:

PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

With the correct PATH, pidof is found, the process count is accurate, and the script behaves as intended.

This simple environment‑variable mismatch caused hours of debugging, illustrating how seemingly trivial differences between cron and interactive shells can lead to hidden bugs.