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Operating Systems AIX Difference between services and process Post 302856887 by bakunin on Wednesday 25th of September 2013 03:02:15 AM
Old 09-25-2013
A "process" is one (or several, see below) string(s) of executable (processor-)instructions with its own environment. This environment is called "process-environment" and consists of memory segments, contents of environment variables, an entry in the process table and maybe other kernel tables and so on.

Notice the difference to the similar "thread", which is also one such string of executable instructions, but without an environment of its own. One or several threads combine to make for a process. How many such threads comprise a process is a matter of how the underlying program is written.

Also notice, that "process" means a single instance of a program. A "program" (a file containing executable instructions) can be started several times. Each time a separate process is created which just happens to contain the same instructions as the other (so-called) "instances" (=processes) of the program.

Processes may or may not constitute "services". A "service" is a process which carries out a specific task and is reachable via a certain network port address. For instance, the "telnet" service, which is a process (telnetd) listening to a certain port (usually 23) for incoming requests. Another example would be the listener of an Oracle database, which propagates the "Oracle service" a system can offer to the world.

Such services can be single-threaded or multi-threaded processes, but what makes them services is their function, not the way they are programmed.

I hope this helps.

bakunin
 

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stopped(7)						 Miscellaneous Information Manual						stopped(7)

NAME
stopped - event signalling that a job has stopped SYNOPSIS
stopped JOB=JOB INSTANCE=INSTANCE RESULT=RESULT [PROCESS=PROCESS] [EXIT_STATUS=STATUS] [EXIT_SIGNAL=SIGNAL] [ENV]... DESCRIPTION
The stopped event is generated by the Upstart init(8) daemon when an instance of a job has stopped. The JOB environment variable contains the job name, and the INSTANCE environment variable contains the instance name which will be empty for single-instance jobs. If the job was stopped normally, the RESULT environment variable will be ok, otherwise if the job was stopped because it has failed it will be failed. When the job has failed, the process that failed will be given in the PROCESS environment variable. This may be pre-start, post-start, main, pre-stop or post-stop; it may also be the special value respawn to indicate that the job was stopped because it hit the respawn limit. Finally in the case of a failed job, one of either EXIT_STATUS or EXIT_SIGNAL may be given to indicate the cause of the stop. Either EXIT_STATUS will contain the exit status code of the process, or EXIT_SIGNAL will contain the name of the signal that the process received. The normal exit job configuration stanza can be used to prevent particular exit status values or signals resulting in a failed job, see init(5) for more information. If neither EXIT_STATUS or EXIT_SIGNAL is given for a failed process, it is because the process failed to spawn (for example, file not found). See the system logs for the error. init(8) emits this event as an informational signal, services and tasks started or stopped by this event will do so in parallel with other activity. It is typically combined with the starting(7) event by services when inserting themselves as a dependency. Job configuration files may use the export stanza to export environment variables from their own environment into the stopped event. See init(5) for more details. EXAMPLE
A service that wishes to be running whenever another service would be running, started before and stopped after it, might use: start on starting apache stop on stopped apache A task that must be run after another task or service has been stopped might use: start on stopped postgresql SEE ALSO
starting(7) started(7) stopping(7) init(5) Upstart 2009-07-09 stopped(7)
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