In 2002 FreeBSD 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 at boot time 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:
natd_enable="YES"
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
“one”. For instance to restart sshd regardless of
the current /etc/rc.conf setting, execute the following
command:
# /etc/rc.d/sshd onerestart
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
Note: The second line (# sshd) is the output from the sshd command, not a root console.
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.
In some cases 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. Support for this feature is not included for every
service.
The rc.d system 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 must be included in all startup scripts (they are required by rc.subr(8) to “enable” the startup script):
PROVIDE: Specifies the services this file provides.
The following words may be included at the top of each startup file. They are not strictly necessary, but they are useful as hints to rcorder(8):
REQUIRE: Lists services which are required for this service. This file will run after the specified services.
BEFORE: Lists services which depend on this service. This file will run before the specified services.
By carefully setting these keywords for each startup script, an administrator has a very fine-grained level of control of the startup order of the scripts, without the hassle of “runlevels” like some other UNIX® operating systems.
Additional information about the rc.d system can be found in the rc(8) and rc.subr(8) manual pages. If you are interested in writing your own rc.d scripts or improving the existing ones, you may find this article also useful.