en/handbook/hb-working-rcscripts.xml

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<sections>
<section>
<title>Runlevels</title>
<subsection>
<title>Booting your System</title>
<body>

<p>
When you boot your system, you will notice lots of text floating by. If you pay
close attention, you will notice this text is the same every time you reboot
your system. The sequence of all these actions is called the <e>boot
sequence</e> and is (more or less) statically defined.
</p>

<p>
First, your boot loader will load the kernel image you have defined in the
boot loader configuration into memory after which it tells the CPU to run the
kernel. When the kernel is loaded and run, it initializes all kernel-specific
structures and tasks and starts the <c>init</c> process.
</p>

<p>
This process then makes sure that all filesystems (defined in
<path>/etc/fstab</path>) are mounted and ready to be used. Then it executes
several scripts located in <path>/etc/init.d</path>, which will start the
services you need in order to have a successfully booted system.
</p>

<p>
Finally, when all scripts are executed, <c>init</c> activates the terminals
(in most cases just the virtual consoles which are hidden beneith <c>Alt-F1</c>,
<c>Alt-F2</c>, etc.) attaching a special process called <c>agetty</c> to it. 
This process will then make sure you are able to log on through these terminals 
by running <c>login</c>.
</p>

</body>
</subsection>
<subsection>
<title>Init Scripts</title>
<body>

<p>
Now <c>init</c> doesn't just execute the scripts in <path>/etc/init.d</path>
randomly. Even more, it doesn't run all scripts in <path>/etc/init.d</path>,
only the scripts it is told to execute. It decides which scripts to execute by 
looking into <path>/etc/runlevels</path>.
</p>

<p>
First, <c>init</c> runs all scripts from <path>/etc/init.d</path> that have
symbolic links inside <path>/etc/runlevels/boot</path>. Usually, it will
start the scripts in alphabetical order, but some scripts have dependency
information in them, telling the system that another script must be run before
they can be started. 
</p>

<p>
When all <path>/etc/runlevels/boot</path> referenced scripts are executed,
<c>init</c> continues with running the scripts that have a symbolic link to them
in <path>/etc/runlevels/default</path>. Again, it will use the alphabetical
order to decide what script to run first, unless a script has dependency
information in it, in which case the order is changed to provide a valid 
start-up sequence.
</p>

</body>
</subsection>
<subsection>
<title>How Init Works</title>
<body>

<p>
Of course <c>init</c> doesn't decide all that by itself. It needs a
configuration file that specifies what actions need to be taken. This
configuration file is <path>/etc/inittab</path>.
</p>

<p>
If you remember the boot sequence we have just explained to you, you will
remember that <c>init</c>'s first action is to mount all filesystems. This is
defined in the following line from <path>/etc/inittab</path>:
</p>

<pre caption="The system initialisation line in /etc/inittab">
si::sysinit:/sbin/rc sysinit
</pre>

<p>
This line tells <c>init</c> that it must run <c>/sbin/rc sysinit</c> to
initialize the system. The <path>/sbin/rc</path> script takes care of the
initialisation, so you might say that <c>init</c> doesn't do much -- it
delegates the task of initialising the system to another process.
</p>

<p>
Second, <c>init</c> executed all scripts that had symbolic links in
<path>/etc/runlevels/boot</path>. This is defined in the following line:
</p>

<pre caption="The system initialisation, continued">
rc::bootwait:/sbin/rc boot
</pre>

<p>
Again the <c>rc</c> script performs the necessary tasks. Note that the option
given to <c>rc</c> (<e>boot</e>) is the same as the subdirectory of
<path>/etc/runlevels</path> that is used.
</p>

<p>
Now <c>init</c> checks its configuration file to see what <e>runlevel</e> it
should run. To decide this, it reads the following line from
<path>/etc/inittab</path>:
</p>

<pre caption="The initdefault line">
id:3:initdefault:
</pre>

<p>
In this case (which the majority of Gentoo users will use), the <e>runlevel</e>
id is 3. Using this information, <c>init</c> checks what it must run to start
<e>runlevel 3</e>:
</p>

<pre caption="The runlevel definitions">
l0:0:wait:/sbin/rc shutdown
l1:S1:wait:/sbin/rc single
l2:2:wait:/sbin/rc nonetwork
l3:3:wait:/sbin/rc default
l4:4:wait:/sbin/rc default
l5:5:wait:/sbin/rc default
l6:6:wait:/sbin/rc reboot
</pre>

<p>
The line that defines level 3, again, uses the <c>rc</c> script to start the
services (now with argument <e>default</e>). Again note that the argument of
<c>rc</c> is the same as the subdirectory from <path>/etc/runlevels</path>.
</p>

<p>
When <c>rc</c> has finished, <c>init</c> decides what virtual consoles it should
activate and what commands need to be run at each console:
</p>

<pre caption="The virtual consoles definition">
c1:12345:respawn:/sbin/agetty 38400 tty1 linux
c2:12345:respawn:/sbin/agetty 38400 tty2 linux
c3:12345:respawn:/sbin/agetty 38400 tty3 linux
c4:12345:respawn:/sbin/agetty 38400 tty4 linux
c5:12345:respawn:/sbin/agetty 38400 tty5 linux
c6:12345:respawn:/sbin/agetty 38400 tty6 linux
</pre>


</body>
</subsection>
<subsection>
<title>What is a runlevel?</title>
<body>

<p>
You have seen that <c>init</c> uses a numbering scheme to decide what
<e>runlevel</e> it should activate. A <e>runlevel</e> is a state in which
your system is running and contains a collection of scripts (runlevel scripts or
<e>initscripts</e>) that must be executed when you enter or leave a runlevel.
</p>

<p>
In Gentoo, there are seven runlevels defined: three internal runlevels, and four
user-defined runlevels. The internal runlevels are called <e>sysinit</e>,
<e>shutdown</e> and <e>reboot</e> and do exactly what their names imply:
initialize the system, powering off the system and rebooting the system.
</p>

<p>
The user-defined runlevels are those with an accompanying
<path>/etc/runlevels</path> subdirectory: <path>boot</path>,
<path>default</path>, <path>nonetwork</path> and <path>single</path>. The
<path>boot</path> runlevel starts all system-necessary services which all other
runlevels use. The remaining three runlevels differ in what services they start:
<path>default</path> is used for day-to-day operations, <path>nonetwork</path>
is used in case no network connectivity is required, and <path>single</path> is
used when you need to fix the system.
</p>

</body>
</subsection>
<subsection>
<title>Working with the Init Scripts</title>
<body>

<p>
The scripts that the <c>rc</c> process starts are called <e>init scripts</e>.
Each script in <path>/etc/init.d</path> can be executed with the arguments
<e>start</e>, <e>stop</e>, <e>restart</e>, <e>pause</e>, <e>zap</e>,
<e>status</e>, <e>ineed</e>, <e>iuse</e>, <e>needsme</e>, <e>usesme</e> or
<e>broken</e>.
</p>

<p>
To start, stop or restart a service (and all depending services), <c>start</c>,
<c>stop</c> and <c>restart</c> should be used:
</p>

<pre caption="Starting Postfix">
# <i>/etc/init.d/postfix start</i>
</pre>

<note>
Only the services that <e>need</e> the given service are stopped or restarted.
The other depending services (those that <e>use</e> the service but don't need
it) are left untouched.
</note>

<p>
If you want to stop a service, but not the services that depend on it, you can
use the <c>pause</c> argument:
</p>

<pre caption="Stopping Postfix but keep the depending services running">
# <i>/etc/init.d/postfix pause</i>
</pre>

<p>
If you want to see what status a service has (started, stopped, paused, ...) you
can use the <c>status</c> argument:
</p>

<pre caption="Status information for postfix">
# <i>/etc/init.d/postfix status</i>
</pre>

<p>
If the status information tells you that the service is running, but you know
that it is not, then you can reset the status information to "stopped" with the 
<c>zap</c> argument:
</p>

<pre caption="Resetting status information for postfix">
# <i>/etc/init.d/postfix zap</i>
</pre>

<p>
To also ask what dependencies the service has, you can use <c>iuse</c> or
<c>ineed</c>. With <c>ineed</c> you can see the services that are really
necessary for the correct functioning of the service. <c>iuse</c> on the other
hand shows the services that can be used by the service, but are not necessary
for the correct functioning.
</p>

<pre caption="Requesting a list of all necessary services on which Postfix depends">
# <i>/etc/init.d/postfix ineed</i>
</pre>

<p>
Similarly, you can ask what services require the service (<c>needsme</c>) or can
use it (<c>usesme</c>):
</p>

<pre caption="Requesting a list of all services that require Postfix">
# <i>/etc/init.d/postfix needsme</i>
</pre>

<p>
Finally, you can ask what dependencies the service requires but that are
missing:
</p>

<pre caption="Requesting a list of missing dependencies for Postfix">
# <i>/etc/init.d/postfix broken</i>
</pre>

</body>
</subsection>
</section>
<section>
<title>Working with rc-update</title>
<subsection>
<title>What is rc-update?</title>
<body>

<p>
Gentoo's init system uses a dependency-tree to decide what service needs to be
started first. As this is a tedious task that we wouldn't want our users to do
manually, we have created tools that ease the administration of the runlevels
and init scripts.
</p>

<p>
With <c>rc-update</c> you can add and remove init scripts to a runlevel. The
<c>rc-update</c> tool will then automatically ask the <c>depscan.sh</c> script
to rebuild the dependency tree.
</p>

</body>
</subsection>
<subsection>
<title>Adding and Removing Services</title>
<body>

<p>
You have already added init scripts to the "default" runlevel during the
installation of Gentoo. At that time you might not have had a clue what the
"default" is for, but now you should. The <c>rc-update</c> script requires a
second argument that defines the action: <e>add</e>, <e>del</e> or <e>show</e>.
</p>

<p>
To add or remove an init script, just give <c>rc-update</c> the <c>add</c> or
<c>del</c> argument, followed by the init script and the runlevel. For instance:
</p>

<pre caption="Removing Postfix from the default runlevel">
# <i>rc-update del postfix default</i>
</pre>

<p>
The <c>rc-update show</c> command will show all the available init scripts and
list at which runlevels they will execute:
</p>

<pre caption="Receiving init script information">
# <i>rc-update show</i>
</pre>

</body>
</subsection>
</section>
<section>
<title>Configuring Services</title>
<subsection>
<title>Why the Need for Extra Configuration?</title>
<body>

<p>
Init scripts can be quite complex. It is therefore not really interesting to 
have the users directly edit the init script, as it would make it more 
error-prone. It is however important to be able to configure such a service. For
instance, you might want to give more options to the service itself.
</p>

<p>
A second reason to have this configuration outside the init script is to be able
to update the init scripts without being afraid that your configuration changes
are undone.
</p>

</body>
</subsection>
<subsection>
<title>The /etc/conf.d Directory</title>
<body>

<p>
Gentoo provides an easy way to configure such a service: every init script that
can be configured has a file in <path>/etc/conf.d</path>. For instance, the
apache2 initscript (called <path>/etc/init.d/apache2</path>) has a
configuration file called <path>/etc/conf.d/apache2</path>, which can contain
the options you want to give to the Apache 2 server when it is started:
</p>

<pre caption="Variable defined in /etc/conf.d/apache2">
APACHE2_OPTS="-D PHP4"
</pre>

<p>
Such a configuration file contains variables and variables alone (just like
<path>/etc/make.conf</path>), making it very easy to configure services. It also
allows us to provide more information about the variables (as comments).
</p>

</body>
</subsection>
</section>
<section>
<title>Writing Init Scripts</title>
<subsection>
<title>Do I Have To?</title>
<body>

<p>
No. Writing an init script is usually not necessary as Gentoo provides
ready-to-use init scripts for all provided services. However, you might have
installed a service without using Portage, in which case you will most likely
have to create an init script.
</p>

<p>
Do not use the init script provided by the service if it isn't explicitly
written for Gentoo: Gentoo's init scripts are not compatible with the init
scripts used by other distributions!
</p>

</body>
</subsection>
<subsection>
<title>Layout</title>
<body>

<p>
The basic layout of an init script is shown below.
</p>

<pre caption="Basic layout of an init script">
#!/sbin/runscript

depend() {
  <comment>(Dependency information)</comment>
}

start() {
  <comment>(Commands necessary to start the service)</comment>
}

stop() {
  <comment>(Commands necessary to stop the service)</comment>
}

restart() {
  <comment>(Commands necessary to restart the service)</comment>
}
</pre>

<p>
Any init script <e>requires</e> the <c>start()</c> function to be defined. All
other sections are optional.
</p>

</body>
</subsection>
<subsection>
<title>Dependencies</title>
<body>

<p>
There are two dependencies you can define: <c>use</c> and <c>need</c>. As we
have mentioned before, the <c>need</c> dependency is more strict than the
<c>use</c> dependency. Following this dependency type you enter the service
you depend on, or the <e>virtual</e> dependency.
</p>

<p>
A <e>virtual</e> dependency is a dependency that a service provides, but that is
not provided solely by that service. Your init script can depend on a system
logger, but there are many system loggers available (metalogd, syslog-ng,
sysklogd, ...). As you cannot <c>need</c> every single one of them (no sensible
system has all these system loggers installed and running) we made sure that
all these services <c>provide</c> a virtual dependency.
</p>

<p>
Let us take a look at the dependency information for the postfix service.
</p>

<pre caption="Dependency information for Postfix">
depend() {
  need net
  use logger dns
  provide mta
}
</pre>

<p>
As you can see, the postfix service:
</p>

<ul>
  <li>
    requires the (virtual) <c>net</c> dependency (which is provided by, for
    instance, <path>/etc/init.d/net.eth0</path>)
  </li>
  <li>
    uses the (virtual) <c>logger</c> dependency (which is provided by, for 
    instance, <path>/etc/init.d/syslog-ng</path>)
  </li>
  <li>
    uses the (virtual) <c>dns</c> dependency (which is provided by, for
    instance, <path>/etc/init.d/named</path>)
  </li>
  <li>
    provides the (virtual) <c>mta</c> dependency (which is common for all mail 
    servers)
  </li>
</ul>

</body>
</subsection>
<subsection>
<title>Controlling the Order</title>
<body>

<p>
In some cases you might not require a service, but want your service to be
started <c>before</c> (or <c>after</c>) another service <e>if</e> it is
available on the system (note the conditional - this is no dependency anymore)
<e>and</e> ran in the same runlevel (note the conditional - only services in the
same runlevel are involved). You can provide this information using the 
<c>before</c> or <c>after</c> settings.
</p>

<p>
As an example we view the settings of the Portmap service:
</p>

<pre caption="The depend() function in the Portmap service">
depend() {
  need net
  before inetd
  before xinetd
}
</pre>

<p>
You can also use the "*" glob to catch all services in the same runlevel,
although this isn't adviseable.
</p>

<pre caption="Running an init script as first script in the runlevel">
depend() {
  before *
}
</pre>

</body>
</subsection>
<subsection>
<title>Standard Functions</title>
<body>

<p>
Next to the <c>depend()</c> functionality, you also need to define the
<c>start()</c> function. This one contains all the commands necessary to
initialize your service. It is adviseable to use the <c>ebegin</c> and
<c>eend</c> functions to inform the user about what is happening:
</p>

<pre caption="Example start() function">
start() {
  ebegin "Starting my_service"
  start-stop-daemon --start --quiet --exec /path/to/my_service
  eend $?
}
</pre>

<p>
If you need more examples of the <c>start()</c> function, please read the source
code of the available init scripts in your <path>/etc/init.d</path> directory.
As for <c>start-stop-daemon</c>, there is an excellent man page available if you
need more information:
</p>

<pre caption="Getting the man page for start-stop-daemon">
# <i>man start-stop-daemon</i>
</pre>

<p>
Other functions you can define are: <c>stop()</c> and <c>restart()</c>. You are
not obliged to define these functions! Our init system is intelligent enough to
fill these functions by itself if you use <c>start-stop-daemon</c>.
</p>

</body>
</subsection>
<subsection>
<title>Adding Custom Options</title>
<body>

<p>
If you want your init script to support more options than the ones we have
already encountered, you should add the option to the <c>opts</c> variable, and
create a function with the same name as the option. For instance, to support an
option called <c>restartdelay</c>:
</p>

<pre caption="Supporting the restartdelay option">
opts="${opts} restartdelay"

restartdelay() {
  stop()
  sleep 3    <comment># Wait 3 seconds before starting again</comment>
  start()
}
</pre>

</body>
</subsection>
<subsection>
<title>Service Configuration Variables</title>
<body>

<p>
You don't have to do anything to support a configuration file in
<path>/etc/conf.d</path>: if your init script is executed, the following files
are automatically sourced (i.e. the variables are available to use):
</p>

<ul>
  <li><path>/etc/conf.d/&lt;your init script&gt;</path></li>
  <li><path>/etc/conf.d/basic</path></li>
  <li><path>/etc/rc.conf</path></li>
</ul>

<p>
Also, if your init script provides a virtual dependency (such as <c>net</c>),
the file associated with that dependency (such as <path>/etc/conf.d/net</path>)
will be sourced too.
</p>

</body>
</subsection>
</section>
<section>
<title>Changing the Runlevel Behaviour</title>
<subsection>
<title>Who might benefit from this?</title>
<body>

<p>
Many laptop users know the situation: at home you need to start <c>net.eth0</c>
while you don't want to start <c>net.eth0</c> while you're on the road (as 
there is no network available). With Gentoo you can alter the runlevel behaviour
to your own will.
</p>

<p>
For instance you can create a second "default" runlevel which you can boot that
has other init scripts assigned to it. You can then select at boottime what
defalt runlevel you want to use.
</p>

</body>
</subsection>
<subsection>
<title>Using SOFTLEVEL</title>
<body>

<p>
First of all, create the runlevel directory for your second "default" runlevel.
As an example we create the <path>offline</path> runlevel:
</p>

<pre caption="Creating a runlevel directory">
# <i>mkdir /etc/runlevels/offline</i>
</pre>

<p>
Add the necessary init scripts to the newly created runlevels. For instance, if
you want to have an exact copy of your current <c>default</c> runlevel but
without <c>net.eth0</c>:
</p>

<pre caption="Adding the necessary init scripts">
# <i>ls /etc/runlevels/default</i>
acpid  domainname  local  net.eth0  netmount  postfix  syslog-ng  vcron
# <i>rc-update add acpid offline</i>
# <i>rc-update add domainname offline</i>
# <i>rc-update add local offline</i>
# <i>rc-update add syslog-ng offline</i>
# <i>rc-update add vixie-cron offline</i>
</pre>

<p>
Now edit your bootloader configuration and add a new entry for the
<c>offline</c> runlevel. For instance, in <path>/boot/grub/grub.conf</path>:
</p>

<pre caption="Adding an entry for the offline runlevel">
title Gentoo Linux Offline Usage
  root (hd0,0)
  kernel (hd0,0)/kernel-2.4.25 root=/dev/hda3 <i>softlevel=offline</i>
</pre>

<p>
Voila, you're all set now. If you boot your system and select the newly added
entry at boot, the <c>offline</c> runlevel will be used instead of the
<c>default</c> one.
</p>

</body>
</subsection>
<subsection>
<title>Using BOOTLEVEL</title>
<body>

<p>
Using <c>bootlevel</c> is completely analogous to <c>softlevel</c>. The only
difference here is that you define a second "boot" runlevel instead of a second
"default" runlevel.
</p>

</body>
</subsection>
</section>
</sections>