When managing multiple servers or deploying cron jobs across environments, maintaining identical cron configurations becomes crucial. The standard crontab format doesn't natively support file inclusion, but there are practical workarounds.

# Method 1: Using the crontab command with input redirection
crontab -l | cat - /path/to/cron_jobs.conf | crontab -

# Method 2: Concatenating multiple files
cat /etc/crontab.base /opt/app/cron/*.conf > /etc/crontab

Modern Linux systems support cron directories:

# For system-wide cron jobs
/etc/cron.d/myapp_jobs

# For user-specific jobs
mkdir -p ~/.cron.d
echo "* * * * * user /path/to/script" > ~/.cron.d/job1

Here's a complete deployment script example:

#!/bin/bash
# deploy_cron.sh

BASE_CRON="/etc/crontab.base"
APP_CRON="/opt/app/deploy/cron.conf"
TEMP_CRON="/tmp/combined_cron"

# Backup existing
crontab -l > /backup/cron_$(date +%Y%m%d).bak

# Combine files
cat ${BASE_CRON} ${APP_CRON} > ${TEMP_CRON}

# Validate syntax
crontab ${TEMP_CRON} || {
    echo "Cron syntax error detected"
    exit 1
}

# Clean up
rm ${TEMP_CRON}

For infrastructure automation:

# ansible playbook snippet
- name: Deploy cron jobs
  hosts: webservers
  tasks:
    - name: Combine cron files
      assemble:
        src: "{{ playbook_dir }}/cron_parts/"
        dest: "/etc/cron.d/application"
        mode: '0644'

Store your cron configurations in Git and use post-receive hooks:

# Sample post-receive hook
#!/bin/bash
while read oldrev newrev refname
do
    if [[ $refname = "refs/heads/master" ]]; then
        git --work-tree=/opt/app --git-dir=/opt/app/.git checkout -f
        /opt/app/scripts/deploy_cron.sh
    fi
done

Always validate cron syntax before deployment:

# Validation script example
validate_cron() {
    local file=$1
    crontab $file 2>&1 | grep -qv "errors detected" || {
        echo "Invalid cron syntax in $file"
        return 1
    }
}

---

When working on collaborative projects, maintaining consistent cron job configurations across multiple servers can become tedious. The standard approach of manually editing each server's crontab via crontab -e doesn't scale well and creates deployment headaches.

Unlike many Unix configuration files, crontab doesn't natively support include directives. The format you proposed:

* * * * * execsomething /blablabla/blah/
* * * * * onemore /blablabla
@include '/home/user/project/crontab.conf'

won't work because crontab parsers don't recognize @include statements.

Here are three proven approaches to achieve file inclusion in crontab:

1. Using cat in Deployment Scripts

The most straightforward method is to concatenate files during deployment:

# In your deployment script
(cat /etc/crontab.local /home/user/project/crontab.conf) | crontab -

2. Directory-based Approach (For System-wide Crontab)

Modern Linux systems often support cron directories:

# Place files in these directories
/etc/cron.d/          # System-wide
/etc/cron.d/project/  # Project-specific (custom)

Files in these directories follow the same format as crontab but can be managed individually.

3. Symbolic Link Strategy

For user-specific crontabs, create a symlink to your project file:

ln -s /home/user/project/crontab.conf /var/spool/cron/crontabs/project_jobs

When implementing any of these solutions:

• Always include comments in your cron files indicating their source
• Use absolute paths for all commands and includes
• Implement file permission checks (crontab files should be 600)
• Consider using version control hooks to validate syntax before deployment

Here's a complete example for a PHP project deployment:

#!/bin/bash
# deploy_cron.sh

PROJECT_DIR="/var/www/project"
CRON_SOURCE="${PROJECT_DIR}/config/cron.conf"
CRON_TEMP="/tmp/project_cron_$$"

# Combine existing crontab with project config
(crontab -l 2>/dev/null; cat "${CRON_SOURCE}") > "${CRON_TEMP}"

# Validate syntax before applying
if grep -q '^[^#]' "${CRON_TEMP}"; then
    crontab "${CRON_TEMP}" && echo "Crontab updated successfully"
else
    echo "Error: Invalid cron syntax detected" >&2
    exit 1
fi

rm -f "${CRON_TEMP}"

For complex scheduling needs, consider:

• Celery Beat for Python projects
• Sidekiq Scheduler for Ruby
• Jenkins or Rundeck for cross-server job management