Master Linux Boot Startup: Systemd, chkconfig, and Crontab Strategies

1. System Services

If a component is installed as a system service, the default service file

xxx.service

resides in

/usr/lib/systemd/system

.

Two ways to enable boot start:

systemctl method

<code>systemctl enable xxx    # enable boot start
systemctl disable xxx   # disable boot start</code>

<code># Check status
systemctl status chronyd.service</code>

Example output shows the service is loaded and active:

<code>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</code>

List enabled or disabled units:

<code>systemctl list-unit-files --state=enabled
systemctl list-unit-files --state=disabled</code>

chkconfig method (more complex)

<code>chkconfig --add xxx && chkconfig --level 3 xxx on/off</code>

chkconfig works only with SysV scripts located in

/etc/init.d

and linked through

/etc/rc.d/rc*.d

. To list SysV services use:

<code>chkconfig --list network</code>

For native systemd services, use

systemctl list-unit-files

or

systemctl list-dependencies [target]

.

Note: systemctl creates a symlink in

/etc/systemd/system/

or

/etc/systemd/user/

pointing to the original service file.

<code># systemctl enable mysqld
Created symlink from /etc/systemd/system/multi-user.target.wants/mysqld.service to /usr/lib/systemd/system/mysqld.service.</code>

To disable boot start:

systemctl disable xxx

Remove the corresponding symlink or service file under

/etc/systemd/system/

or

/etc/systemd/user/

2. General Solutions

Regardless of whether a component is a system service, you can achieve boot start by using startup scripts. Ensure the script is executable (

chmod +x

).

Method 1: Append the start command to

/etc/rc.local

(or

/etc/rc.d/rc.local

, which is a symlink).

Method 2: Place a

.sh

script in

/etc/profile.d

.

Method 3: Append the command to

/etc/rc.local

as in Method 1.

3. Crontab Solution

crontab supports special keywords prefixed with

@

that replace the five time fields.

<code>@reboot   : Run once after reboot (executes 1‑2 s earlier than /etc/rc.d/rc.local)
@yearly   : Run once a year ("0 0 1 1 *")
@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 * * * *")</code>

Example using

@reboot

for boot start:

<code># crontab -e
@reboot /usr/local/daemonProcess/somescript.sh
* * * * * /usr/local/daemonProcess/somescript.sh</code>

If both

@reboot

and a regular schedule are used, ensure they do not cause duplicate execution within the first minute unless the service tolerates it.

4. Production Environment Recommendation

In production, adopt only one of the three schemes for all components to simplify operations, reduce maintenance cost, and avoid errors during service upgrades.

Appendix: Boot Script Example

<code># chmod +x /etc/rc.d/rc.local
# /usr/local/AutoStartOnBoot.sh
chmod +x /usr/local/AutoStartOnBoot.sh
source /etc/profile
# redis
/usr/local/redis/redis-5.0.13/bin/redis-server /usr/local/redis/redis-5.0.13/conf/redis.conf
# zookeeper (remove old pid then start)
rm -f /data/zookeeper/data/zookeeper_server.pid
/usr/local/apache-zookeeper-3.6.3-bin/bin/zkServer.sh 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
# kafka-manager
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 &
# mysql
service mysqld start</code>