This is the first time I've dealt with runlevels, and it seems Debian is an exception in the Linux world.
My question is whether I understand this correctly: (please excuse the crummy GIMP job)
http://www.linuxquestions.org/questi...1&d=1432890577
I've installed a service that starts in runlevel 1 (which as far as I can tell only is entered after runlevel 2) to update the system.

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runlevels are not executed sequentially, and 2 doesn't call 1 (or 3 calling 4, etc). the desired run level is executed directly, so if its run level 5 for multi-user with GUI init goes directly to rc.5, it doesn't go through 1-4 first.

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Debian seems to use runlevel 0,1,2,6

0=shutdown
1=single user
2=multi-user+gui, if gui is installed
6=reboot

3 (multi-user,no gui, appears to be missing)

Perhaps someone else can enlighten further?

Fred.

debian run levels 3,4 and 5 are the same as 2.
http://www.debian-administration.org..._to_run-levels

A runlevel is nothing more than a bunch of scripts being executed when a runlevel is entered or exited. By convention 1 is single user, 6 is reboot and (I think 7 is halt).

RedHat derivatives use 3 for text mode and 5 for GUI. Debian uses 2 for GUI.

There is no convention for runlevels 2-5 so anyone can use them at will. However Debian seems to go here against the most common use of RL=3 for GUI.

Runlevels are not executed in sequence, but you can call one runlevel from the other. So start in RL=1 in single user mode and then change to RL=2 or RL=5 to get a GUI. But you can even do that manually.

jlinkels

Thank you for clearing that up. I am pretty certain Debian starts out in runlevel S though, and uses 6 for reboot. I am not sure where and when runlevel 1 comes into play with Debian.
As I understand it only when entered.

Run levels are a way of setting up a computer in different ways for different use cases.
You can create your own by using 2~5, ( runlevels 0,1,& 6 are usually predefined & would cause great confusion if altered).
eg: Single user - multi user console - multi user GUI - with wifi - without wifi - etc, etc.

Debian 8 no longer uses runlevels.
http://www.freedesktop.org/wiki/Soft...skedQuestions/

The correct explanation is that each runlevel defines a number of services which should be stopped and services which should start. The services which must be stopped when entering a runlevel have a symbolic link name Knn<scriptname> and those which must be started Snn<scriptname>.
Indeed is the stopping and starting only defined when a runlevel is entered.

jlinkels

True, debian 8 uses systemd but the OP did not post the currently running version.

Generally you run a system in 3 stages.

Stage 1: booting - init brings up kernel and activates core system services like udev and networking.
Stage 2: cruising - init or service supervisor activates non-core services and enters usermode for general usage.
Stage 3: halting - init halts system services for reboot or shutdown sequences.

This is universal to any init system. What constitutes a runlevel is a configuration of services launched at stage 2 for the user of the system. Systemd actually does use runlevels, but uses an open ended configuration similar to s6, runit, OpenRC, and such where the system admin can add or remove services ran from the default system runlevel before the login prompt is activated.