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

1. System Services

If a component is installed as a system service, its default service file (e.g., xxx.service) resides in /usr/lib/systemd/system.

You can enable or disable boot‑time start in two ways.

systemctl method

systemctl enable/disable xxx   # enable or disable boot start
systemctl status chronyd.service   # check if enabled
# Example output shows the service is loaded and active
systemctl list-unit-files   # list all unit files and their enable state
systemctl list-unit-files --state=enabled   # list enabled services
systemctl is-enabled xxx   # check a specific service
systemctl list-unit-files --state=disabled   # list disabled services
systemctl --state=help   # help for state options

Note: the systemctl approach creates a symlink under /etc/systemd/system/ (or /etc/systemd/user/) pointing to the original service file.

chkconfig method (more complex)

chkconfig --add xxx && chkconfig --level 3 xxx on/off
# Service scripts must reside in /etc/init.d/ and be linked in /etc/rc.d/rc*.d
chkconfig --list network   # list SysV services (does not include 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]'

To disable boot start with systemctl you can either run systemctl disable xxx or remove the corresponding symlink from /etc/systemd/system/ or /etc/systemd/user/.

2. General Approach

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

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

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

Or append the execution command to /etc/rc.local / /etc/rc.d/rc.local from a custom script.

3. Crontab Approach

Crontab supports special keywords prefixed with @ to replace the five‑field time specification.

@reboot   : Run once after reboot (executes earlier than /etc/rc.d/rc.local by ~1‑2 seconds).
@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 to start a daemon at boot:

# crontab -e
@reboot /usr/local/daemonProcess/somescript.sh
# Daemon keep‑alive every minute
* * * * * /usr/local/daemonProcess/somescript.sh

Use @reboot together with regular schedules only when the workload tolerates possible duplicate executions within the first minute after boot.

4. Production Environment Startup Recommendations

In production, adopt a single startup method for all components to simplify operations and reduce error risk. Some services may not provide native systemd units, making the generic script approach preferable.

Appendix: Startup Script Examples

# Add commands to /etc/rc.local (or its symlink /etc/rc.d/rc.local)
# Write a script.sh and place it in /etc/profile.d
chmod +x /etc/rc.d/rc.local
# Example boot script
/usr/local/AutoStartOnBoot.sh
chmod +x /usr/local/AutoStartOnBoot.sh
# Load environment variables before starting services
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 stale pid first)
rm -f /data/zookeeper/data/zookeeper_server.pid
/usr/local/apache-zookeeper-3.6.3-bin/bin/zkServer.sh start
# Start Kafka with JMX port
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 stale 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