X-Git-Url: http://pere.pagekite.me/gitweb/homepage.git/blobdiff_plain/f71e4611e36087db31e02d79d1a10fc1220bcb08..98679f388f037668a403d76a4a1b455376920ece:/blog/index.rss diff --git a/blog/index.rss b/blog/index.rss index 1e377557f9..5c3145202f 100644 --- a/blog/index.rss +++ b/blog/index.rss @@ -6,6 +6,74 @@ http://people.skolelinux.org/pere/blog/ + + How is booting into runlevel 1 different from single user boots? + http://people.skolelinux.org/pere/blog/How_is_booting_into_runlevel_1_different_from_single_user_boots_.html + http://people.skolelinux.org/pere/blog/How_is_booting_into_runlevel_1_different_from_single_user_boots_.html + Thu, 4 Aug 2011 12:40:00 +0200 + +<p>Wouter Verhelst have some +<a href="http://grep.be/blog/en/retorts/pere_kubuntu_boot">interesting +pcomments and opinions</a> on my blog post on +<a href="http://people.skolelinux.org/pere/blog/What_should_start_from__etc_rcS_d__in_Debian____almost_nothing.html">the +need to clean up /etc/rcS.d/ in Debian</a> and my blog post about +<a href="http://people.skolelinux.org/pere/blog/What_is_missing_in_the_Debian_desktop__or_why_my_parents_use_Kubuntu.html">the +default KDE desktop in Debian</a>. I only have time to address one +small piece of his comment now, and though it best to address the +misunderstanding he bring forward:</p> + +<p><blockquote> +Currently, a system admin has four options: [...] boot to a +single-user system (by adding 'single' to the kernel command line; +this runs rcS and rc1 scripts) +</blockquote></p> + +<p>This make me believe Wouter believe booting into single user mode +and booting into runlevel 1 is the same. I am not surprised he +believe this, because it would make sense and is a quite sensible +thing to believe. But because the boot in Debian is slightly broken, +runlevel 1 do not work properly and it isn't the same as single user +mode. I'll try to explain what is actually happing, but it is a bit +hard to explain.</p> + +<p>Single user mode is defined like this in /etc/inittab: +"<tt>~~:S:wait:/sbin/sulogin</tt>". This means the only thing that is +executed in single user mode in sulogin. Single user mode is a boot +state "between" the runlevels, and when booting into single user mode, +only the scripts in /etc/rcS.d/ are executed before the init process +enters the single user state. When switching to runlevel 1, the state +is in fact not ending in runlevel 1, but it passes through runlevel 1 +and end up in the single user mode (see /etc/rc1.d/S03single, which +runs "init -t1 S" to switch to single user mode at the end of runlevel +1. It is confusing that the 'S' (single user) init mode is not the +mode enabled by /etc/rcS.d/ (which is more like the initial boot +mode).</p> + +<p>This summary might make it clearer. When booting for the first +time into single user mode, the following commands are executed: +"<tt>/etc/init.d/rc S; /sbin/sulogin</tt>". When booting into +runlevel 1, the following commands are executed: "<tt>/etc/init.d/rc +S; /etc/init.d/rc 1; /sbin/sulogin</tt>". A problem show up when +trying to continue after visiting single user mode. Not all services +are started again as they should, causing the machine to end up in an +unpredicatble state. This is why Debian admins recommend rebooting +after visiting single user mode.</p> + +<p>A similar problem with runlevel 1 is caused by the amount of +scripts executed from /etc/rcS.d/. When switching from say runlevel 2 +to runlevel 1, the services started from /etc/rcS.d/ are not properly +stopped when passing through the scripts in /etc/rc1.d/, and not +started again when switching away from runlevel 1 to the runlevels +2-5. I believe the problem is best fixed by moving all the scripts +out of /etc/rcS.d/ that are not <strong>required</strong> to get a +functioning single user mode during boot.</p> + +<p>I have spent several years investigating the Debian boot system, +and discovered this problem a few years ago. I suspect it originates +from when sysvinit was introduced into Debian, a long time ago.</p> + + + Fint at militæret ikke ble aktivisert 22. juli http://people.skolelinux.org/pere/blog/Fint_at_milit__ret_ikke_ble_aktivisert_22__juli.html @@ -440,24 +508,5 @@ utviklingstimer for å en norsk portal på plass.</p> - - Free Software vs. proprietary softare... - http://people.skolelinux.org/pere/blog/Free_Software_vs__proprietary_softare___.html - http://people.skolelinux.org/pere/blog/Free_Software_vs__proprietary_softare___.html - Mon, 20 Jun 2011 12:50:00 +0200 - -<p>Reading -<a href="http://blog.thingiverse.com/2011/06/20/open-source-vs-closed-source-eulas/">the -thingiverse blog</a>, I came across two highlights of interesting -parts of the -<a href="http://wiki.blender.org/index.php/Autodesk_EULA">Autodesk</a> -and -<a href="http://blog.makezine.com/archive/2011/06/things-you-cant-do-with-the-microsoft-kinect-sdk.html">Microsoft -Kinect</a> End User License Agreements (EULAs), which illustrates -quite well why I stay away from software with EULAs. Whenever I take -the time to read their content, the terms are simply unacceptable.</p> - - -