Master Linux Startup: Systemd, chkconfig, and Crontab Methods Explained

1. System Services

If a component is installed as a system service, the default service file is xxx.service located in /usr/lib/systemd/system.

Two ways to enable boot start:

systemctl method

systemctl enable/disable xxx    # enable or disable boot start
# Check boot start status
systemctl status chronyd.service
# Example output (truncated)
● chronyd.service - NTP client/server
   Loaded: loaded (/usr/lib/systemd/system/chronyd.service; enabled; vendor preset: enabled)
   Active: active (running) since Thu 2022-07-28 18:33:39 CST; 4 months 4 days ago
   Docs: man:chronyd(8) man:chrony.conf(5)
   Main PID: 790 (chronyd)
   Memory: 1.0M
   CGroup: /system.slice/chronyd.service
       └─790 /usr/sbin/chronyd
# List unit files and their enable state
systemctl list-unit-files --state=enabled
systemctl list-unit-files --state=disabled
# Help for --state option
systemctl --state=help

chkconfig method (more complex)

chkconfig --add xxx && chkconfig --level 3 xxx on/off
# This method requires the service script to be in /etc/init.d/ and linked in /etc/rc.d/rc0.d~rc6.d.
# Check boot start status for SysV services
chkconfig --list network
# Note: output shows only SysV services, not native systemd services.
# To list systemd services use:
# systemctl list-unit-files
# To see services enabled for a specific target use:
# systemctl list-dependencies [target]

Special note: systemctl effect

The systemctl method creates a symbolic link for the .service file under /etc/systemd/system/ or /etc/systemd/user/, representing system‑wide or user‑specific services. The target directory (e.g., multi-user.target.wants) determines when the service starts.

# Enable MySQL service
systemctl enable mysqld
# Result: Created symlink from /etc/systemd/system/multi-user.target.wants/mysqld.service to /usr/lib/systemd/system/mysqld.service.

To disable boot start, either run systemctl disable xxx or remove the corresponding symlink or service file.

2. General Solution

Regardless of whether a component is already a system service, you can use a boot‑start script. Remember to make the script executable ( chmod +x).

Add the start command to the default script /etc/rc.local (or its symlink /etc/rc.d/rc.local).

Create a .sh script and place it in /etc/profile.d.

Append the execution command to /etc/rc.local or /etc/rc.d/rc.local from a custom script.

3. Crontab Solution

Crontab supports special keywords prefixed with @ to replace the five time fields. Common forms:

@reboot   : Run once after reboot (executes earlier than /etc/rc.d/rc.local).
@yearly   : Run once a year ("0 0 1 1 *").
@annually : Same as @yearly.
@monthly  : Run once a month ("0 0 1 * *").
@weekly   : Run once a week ("0 0 * * 0").
@daily    : Run once a day ("0 0 * * *").
@hourly   : Run once an hour ("0 * * * *").

Example using @reboot for a daemon:

# Edit crontab
crontab -e
# Add job definition
@reboot /usr/local/daemonProcess/somescript.sh
# Optional daemon loop (run every minute)
* * * * * /usr/local/daemonProcess/somescript.sh

Special note: Decide whether to use both @reboot and a regular schedule based on your application’s tolerance for duplicate starts.

4. Production‑Environment Startup Recommendation

In production, adopt a single, unified startup method for all components to simplify operations. Mixing different methods can increase maintenance cost and error probability, especially when services are added, removed, or upgraded.

Appendix: Startup Script Example

# Make rc.local executable
chmod +x /etc/rc.d/rc.local
# Example startup script
/usr/local/AutoStartOnBoot.sh
chmod +x /usr/local/AutoStartOnBoot.sh
# Load environment variables
source /etc/profile
# Start Redis
/usr/local/redis/redis-5.0.13/bin/redis-server /usr/local/redis/redis-5.0.13/conf/redis.conf
# Start Zookeeper (remove old pid first)
rm -f /data/zookeeper/data/zookeeper_server.pid;
/usr/local/apache-zookeeper-3.6.3-bin/bin/zkServer.sh start
# Start Kafka
JMX_PORT=9999 /usr/local/kafka_2.13-2.7.1/bin/kafka-server-start.sh -daemon /usr/local/kafka_2.13-2.7.1/config/server.properties
# Start Kafka‑Manager (remove old pid first)
rm -f /usr/local/kafka-manager-2.0.0.2/RUNNING_PID
nohup /usr/local/kafka-manager-2.0.0.2/bin/kafka-manager -Dconfig.file=/usr/local/kafka-manager-2.0.0.2/conf/application.conf -Dhttp.port=9002 >/dev/null 2>&1 &
# Start MySQL
service mysqld start