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SME Server:Documentation:Developers Manual:Chapter9 (view source)
Revision as of 13:32, 25 April 2008
, 13:32, 25 April 2008Adjusting header(s)
<div class="CHAPTER">
<div class="CHAPTER">
=Process startup, supervision and shutdown=
==Process startup, supervision and shutdown==
<div class="SECT1">
<div class="SECT1">
==Process startup==
===Process startup===
In typical Linux systems, services (processes) are started at boot time through a mechanism such as <span class="emphasis">''System V init''</span>. When the system administrator needs to change the settings, they modify the configuration files and then restart the service or notify the process that it needs to re-read the configuration.
In typical Linux systems, services (processes) are started at boot time through a mechanism such as <span class="emphasis">''System V init''</span>. When the system administrator needs to change the settings, they modify the configuration files and then restart the service or notify the process that it needs to re-read the configuration.
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==Process supervision: runit (and supervise)==
===Process supervision: runit (and supervise)===
The SME Server addresses these issues by running processes under the '''runit''' process supervision environment, which:
The SME Server addresses these issues by running processes under the '''runit''' process supervision environment, which:
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===The runit process tree===
====The runit process tree====
When a Linux system boots, it starts the '''init''' process, which then starts all other processes. When '''init''' enters "run-level 7", it starts '''/etc/runit/2''' from an entry in <tt class="FILENAME">/etc/inittab</tt>.
When a Linux system boots, it starts the '''init''' process, which then starts all other processes. When '''init''' enters "run-level 7", it starts '''/etc/runit/2''' from an entry in <tt class="FILENAME">/etc/inittab</tt>.
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===Run-level 7 and the e-smith-service wrapper===
====Run-level 7 and the e-smith-service wrapper====
The SME Server runs in the normally unused run-level 7. This ensures that the only software running on the SME Server is software that we have chosen to run, and it is started and stopped in a consistent way. If we need to replace a standard startup script with one which runs the process under supervise, we can do so <span class="emphasis">''without modifying the original package''</span>.
The SME Server runs in the normally unused run-level 7. This ensures that the only software running on the SME Server is software that we have chosen to run, and it is started and stopped in a consistent way. If we need to replace a standard startup script with one which runs the process under supervise, we can do so <span class="emphasis">''without modifying the original package''</span>.