cron, atd, anacron, other wtf

[John Richard Moser]

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Matthew Garrett wrote:
> On Tue, Jan 10, 2006 at 11:52:43PM -0500, John Richard Moser wrote:
> 
> 
>> S89cron
>> S89anacron
>> S89atd:    Periodic Command schedulers -- THREE?  Please pick one to
>>            use and stick with it.  If we need to use others, we'll turn
>>            them on, we obviously know what we're doing if we know we
>>            need any of these
> 
> 
> There's a clear difference between these three applications, and merging 
> them would be a fairly significant amount of development effort.
> 
> cron - executes recurring commands that should occur at a specific time
> anacron - executes recurring commands that should take place with a 
>  given frequency. 
> 
> (The difference between them is that if a task is scheduled in cron and 
> the machine is switched off, it won't be executed until the next time 
> it's due to run. anacron will attempt to catch up when the machine comes 
> back up)
> 
> atd - executes a non-recurring command at a specific time
> 
> The fact that all three exist is something of a holdover from legacy 
> Unix, but it's not possible to just remove one of them.
> 

Right, good points all around.  The question arises, are these all used
in default Ubuntu desktop?  If so, is there a way to eliminate the use
of one of them?  Update manager for example should probably be anacron;
that's all I can think of, and I think it uses an update daemon anyway.
. . .

> 
>>The question of sysklogd and klogd comes to mind as well-- are these
>>different, do we need 2?
> 
> 
> They are different, yes. sysklogd starts the system logger (responsible 
> for tracking events that come from userspace), and klogd starts the 
> kernel logger (responsible for tracking events that come from the 
> kernel).
> 

Thought so; I remember one of the daemons on Gentoo available for
syslogging (metalog, sysklogd, some other one I can't recall) had 2 rc
scripts.  I never paid much mind to these, so it was worth asking :)

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