When dealing with persistent background processes that run indefinitely once started through cron, we need a mechanism to ensure single execution while still maintaining the reliability of cron's scheduling system. The traditional cron approach isn't designed for one-off executions of persistent services.

Here are three robust methods to achieve this, each with different trade-offs:

The most reliable approach for production systems:

#!/bin/bash
LOCK_FILE=/tmp/my_job.lock

if [ ! -f "$LOCK_FILE" ]; then
    touch "$LOCK_FILE"
    /path/to/your/command --persistent-flag &
    # Optionally remove lock file when process ends (requires monitoring)
else
    echo "Job already running" >&2
fi

For modern Linux systems with systemd:

# /etc/systemd/system/my-job.service
[Unit]
Description=My one-time job

[Service]
Type=oneshot
ExecStart=/path/to/your/command
RemainAfterExit=yes

[Install]
WantedBy=multi-user.target

Then enable it with:
systemctl enable my-job.service

For systems without systemd:

*/5 * * * * pgrep -f "/path/to/your/command" || /path/to/your/command &

To ensure execution after reboot while maintaining single-instance guarantee:

@reboot flock -n /tmp/my_job.lock -c "/path/to/your/command &"

For enterprise-grade solution with logging and monitoring:

#!/bin/bash
LOCK_DIR=/tmp/my_job.lock.d
LOG_FILE=/var/log/my_job.log

if mkdir "$LOCK_DIR" 2>/dev/null; then
    trap 'rm -rf "$LOCK_DIR"' EXIT
    echo "$(date): Starting job" >> "$LOG_FILE"
    /path/to/your/command >> "$LOG_FILE" 2>&1 &
    echo "$(date): Job started (PID $!)" >> "$LOG_FILE"
else
    echo "$(date): Job already running" >> "$LOG_FILE"
    exit 1
fi

---

When dealing with persistent processes (services/daemons) that run indefinitely once launched, traditional cron scheduling becomes problematic. The standard cron syntax lacks native support for single-execution jobs, which creates complications when you need to:

• Initialize a background service on system reboot
• Run a maintenance script exactly once after deployment
• Trigger a long-running process without creating duplicates

Here are three reliable approaches to achieve one-time execution while maintaining process persistence:

1. The Lockfile Technique

The most robust method combines cron with file-based locking:

#!/bin/bash
LOCKFILE=/tmp/myjob.lock

if [ -e $LOCKFILE ]
then
    echo "Job already running" >&2
    exit 1
else
    touch $LOCKFILE
    /path/to/your/persistent/process &
    # No need to remove lockfile for persistent processes
fi

Schedule this in crontab with:

@reboot /path/to/above/script.sh

2. Systemd Service Integration

For modern Linux systems, systemd provides better control:

# /etc/systemd/system/one-time.service
[Unit]
Description=One-time service starter

[Service]
Type=simple
ExecStart=/path/to/your/daemon
RemainAfterExit=yes

[Install]
WantedBy=multi-user.target

Then enable with:

sudo systemctl enable one-time.service

3. Temporary Cron Entry

For manual one-time execution, use this bash function:

function add_one_time_job() {
    local cmd="$1"
    local temp_cron=$(mktemp)
    
    # Add to temporary crontab
    echo "* * * * * $cmd" >> $temp_cron
    echo "* * * * * crontab -r" >> $temp_cron  # Self-destruct
    
    crontab $temp_cron
    rm $temp_cron
}

When implementing these solutions, pay attention to:

• Process monitoring - use supervisord or similar for crash recovery
• Resource limits - configure memory/CPU constraints
• Log rotation - essential for long-running processes
• User permissions - especially when running as system services

Here's a complete deployment-ready solution for a Node.js service:

#!/usr/bin/env bash

# one-time-node.sh
SERVICE_DIR="/opt/node-service"
LOCK_FILE="/var/run/node-service.lock"
LOG_FILE="/var/log/node-service.log"

if [ -f $LOCK_FILE ]; then
    echo "$(date): Service already running" >> $LOG_FILE
    exit 0
fi

touch $LOCK_FILE
cd $SERVICE_DIR
nohup node server.js >> $LOG_FILE 2>&1 &

Cron entry for reboot execution:

@reboot /bin/bash /usr/local/bin/one-time-node.sh