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:
# service 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, sshd restart 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:
# service 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:
# service sshd rcvar # sshd $sshd_enable=YES
Note: The second line (# sshd) is the output from sshd, not a root console.
To determine whether or not a service is running, use
status
. For instance, to verify that
sshd is running:
# service 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, when the bgfsck 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 rc(8) and rc.subr(8). Refer to this article for instructions on how to create custom rc.d scripts.