System services

---------------



"daemon"

...this word is used below. It means an application that when executed, runs

continually in the background.



The scripts in /etc/init.d are executed at bootup and shutdown to start and stop

services.



At bootup, the /etc/rc.d/rc.services script will run all executable scripts

found in /etc/init.d, with the commandline parameter 'start'.

At shutdown, the /etc/rc.d/rc.shutdown script will run all executable scripts

found in /etc/init.d, with the commandline parameter 'stop'.



Puppies built from the Woof build system after January 26, 2010, have System

Service Management provided in the BootManager (see Sysytem menu).

This Services Manager controls which of these scripts will run by setting or

clearing their 'executable' flag -- a script flagged as executable will run,

otherwise not.



System Services Management

--------------------------



Most users do not normally need to disable any of the system services, however

sometimes there might be a need. 



Each service uses CPU and memory resources, so with a slow CPU there may be

some noticeable gain in not running services that are not needed.



On rare occasions a service may cause trouble, so needs to be disabled.



Here are some notes on particular services:



cups

----

This runs the CUPS daemon 'dbusd', required for printing. Leave this enabled unless

you don't need to print.



messagebus

----------

Runs the daemon 'dbusd'.

DBUS is a method for applications to communicate with one another. Only certain

applications use this, and most puppies are built with apps that don't.

If 'messagebus' script is present, it probably means some application is installed

that needs DBUS. An example is 'gecko-mediaplayer' (browser plugin) that uses DBUS

to communicate with 'gnome-mplayer' (multimedia player). So, unless you know

that no apps require this, leave it enabled.



rc.acpi

-------

Runs the daemon 'acpid'.

This is a daemon that provides certain ACPI management functions. Puppy will

still work without it.



rc.firewall

-----------

In most puppies this scipt is actually located at /etc/rc.d. If you have Internet

access then this is essential to provide protection. It doesn't actually launch

any daemon, only loads kernel modules, so runtime resource usage is low. 

The only time that you might want to disable it is when testing the Internet

connection.



slmodem

-------

Runs the daemon 'slmodemd'.

This provides support for some analog dialup modems. There are reports that

this can conflict with sound on some PCs, so if you don't use an analog modem

for Internet access, or a different modem driver, consider disabling this.



sys_logger

----------

This runs the daemons 'syslogd' and 'klogd', which log kernel and application

events (espcially error messages) to various log files, mostly to 

/var/log/messages. This can be disabled and Puppy will still work.



udev

----

Runs the daemons 'udevd' and 'pup_event_frontend_d'.

This is a mechanism that receives information about hardware events from the kernel,

such as a USB pen drive being plugged in or removed. If you don't want automatic

detection of hardware changes while Puppy is running, Puppy will still work

and you will save quite a lot of CPU usage and resources -- worth considering

this one on a very slow CPU.

This one is different from those listed above, as 'udevd' is essential during

bootup. However, it can be killed after bootup -- it involves the daemon 'udevd'

and the daemon 'pup_event_frontend_d' and if disabled these two are killed when

X is started. The technical description is that when X starts, /root/.xinitrc

runs, which launches /sbin/pup_event_frontend_d -- look in that latter script

and you will see that it reads /etc/eventmanager which has a variable 'BACKENDON'

that can be set to kill udevd and pup_event_frontend_d.

There is a GUI manager for this, the EventManager (see System menu), and changing

the 'udev' checkbox will cause the EventManager to run.





Technical notes

---------------



At startup, the system services are executed by /etc/rc.d/rc.services, which

in turn is called from /etc/rc.d/rc.sysinit.



At shutdown, the system servcies are executed (with the 'stop' parameter) by

/etc/rc.d/rc.shutdown.



Puppy does not have runlevels (basically because Busybox doesn't, at least that

was the original reason). Normal Linux distros would have a list of services to

start for each runlevel, but apart from not having runlevels Puppy also only

runs a very minimum essential set of services, that most users would not want

to tamper with.



Note that /etc/rc.d/init.d is a symlink to /etc/init.d



Note, the scripts in /etc/init.d can have any name, but must have their executable

flag set. Any file that does not have the 'x' flag set will be ignored.



Event Management, which is mostly concerned with hardware-related detection and

configuration while X is running, is described in more detail on this web page:



http://puppylinux.com/technical/event-management.htm



Regards,

Barry Kauler

Jan. 2010