[NTLUG:Discuss] init differences

[Leroy Tennison]

Chris Cox wrote:
> Leroy Tennison wrote:
>> Learned recently that other *NIX use cumulative run levels where it 
>> appears that Linux puts links to every script needed for a given run 
>> level in it's rc?.d directory.  Is there a reason for this or is it just 
>> stylistic preference?
>>
>> Also, seems that SuSE has more run levels than Red Hat (particularly S 
>> unless Red Hat has added that since I last used it), is there a good 
>> reason why?
> 
> In the Unix/Linux world (for those that use a System V style init), the
> runlevels should be viewed as simply definitions of a "state".  That is,
> there is no correlation between runlevels.  Each one stands on its own
> and can be defined however you want.
> 
> That means that there are really no standards for runlevels.  However,
> there is general practice that runlevel 1 means single user, 6 means
> shutdown and reboot and 0 means halt (and/or sometimes poweroff).
> 
> On Linux distros using a SysV style init, runlevel 2 is multiuser.
> Often times, runlevel 3 is runlevel 3 with network services that are rpc
> based (e.g. NFS, NIS, etc) and runlevel 5 is similar to 3 but with an
> Xserver (usually a login display manager) started.
> 
> What I just said is NOT a hard and fast rule across all Linux though...
> so you WILL find systems that might use runlevel 4, you might find some
> that include X Server all of the time when going to any multiuser
> capable runlevel.
> 
> The idea of putting the init scripts into a common directory and
> symlinking them into the runlevel directories is also not always the
> case, but a very common practice.  On Linux distros usually /etc/init.d
> holds the scripts and as you said, they are symlinked starting with SXX
> or KXX into the runlevel areas,  The SXX symlinked ones will make the
> runlevel master script invoke the individual scripts with the argument
> "start" and the KXX ones with the argument "stop".  The initial kickoff
> of what happens when entering a runlevel is handled via /etc/inittab.
> That's where you see the runlevel script manager getting kicked off.
> 
> If you're a Solaris user before Solaris 10, you'll noticed that Sun
> didn't understand what SysV runlevels were (Sun used to use a BSD based
> OS), and so Sun made their runlevel 3 dependent upon runlevel 2.  That
> is just wrong and somewhat embarrassing.  Solaris 10 removed that piece
> of stupidity by replacing scripted init with something more closed (and
> more hideous).
> 
> 
> 
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> 
It's obviously been a while since this message but that's been work - 
busy (which is far better than worried about an imminent layoff).  Tell 
me more about stupidity and hideous.  What are the drawbacks to 
dependent runlevels?  I knew they replaced scripted init with something 
(I heard they called it the registry - if this is true: Really, REALLY 
bad move after M$ use of the term).  What is it and what is hideous.