Contributed by Tom Rhodes.
FreeBSD has recently integrated the NetBSD rc.d system for system initialization. Users should notice the files listed in the /etc/rc.d directory. Many of these files are for basic services which can be controlled with the start, stop, and restart options. For instance, sshd(8) can be restarted with the following command:
# /etc/rc.d/sshd restart
This procedure is similar for other services. Of course, services are usually started automatically as specified in rc.conf(5). For example, enabling the Network Address Translation daemon at startup is as simple as adding the following line to /etc/rc.conf:
If a natd_enable="NO" line is already present, then simply change the NO to YES. The rc scripts will automatically load any other dependent services during the next reboot, as described below.
Since the rc.d system is primarily intended to start/stop services at system startup/shutdown time, the standard start, stop and restart options will only perform their action if the appropriate /etc/rc.conf variables are set. For instance the above sshd restart command will only work if sshd_enable is set to YES in /etc/rc.conf. To start, stop or restart a service regardless of the settings in /etc/rc.conf, the commands should be prefixed with ``force''. For instance to restart sshd regardless of the current /etc/rc.conf setting, execute the following command:
# /etc/rc.d/sshd forcerestart
It is easy to check if a service is enabled in /etc/rc.conf by running the appropriate rc.d script with the option rcvar. Thus, an administrator can check that sshd is in fact enabled in /etc/rc.conf by running:
# /etc/rc.d/sshd rcvar # sshd $sshd_enable=YES
To determine if a service is running, a status option is available. For instance to verify that sshd is actually started:
# /etc/rc.d/sshd status sshd is running as pid 433.
It is also possible to reload a service. This will attempt to send a signal to an individual service, forcing the service to reload its configuration files. In most cases this means sending the service a SIGHUP signal.
The rcNG structure is not only used for network services, it also contributes to most of the system initialization. For instance, consider the bgfsck file. When this script is executed, it will print out the following message:
Starting background file system checks in 60 seconds.
Therefore this file is used for background file system checks, which are done only during system initialization.
Many system services depend on other services to function properly. For example, NIS and other RPC-based services may fail to start until after the rpcbind (portmapper) service has started. To resolve this issue, information about dependencies and other meta-data is included in the comments at the top of each startup script. The rcorder(8) program is then used to parse these comments during system initialization to determine the order in which system services should be invoked to satisfy the dependencies. The following words may be included at the top of each startup file:
By using this method, an administrator can easily control system services without the hassle of ``runlevels'' like some other UNIX® operating systems.
This, and other documents, can be downloaded from ftp://ftp.FreeBSD.org/pub/FreeBSD/doc/.