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An introduction to run-levels

Posted by tsstahl on Fri 12 Aug 2005 at 14:26

Simply put, a 'runlevel' determines which programs are executed at system startup. Most of your exposure to run levels will deal with system startup. You will become intimately familiar with the exceptions the first time you have to troubleshoot a failed system.

Linux run levels are numbered 0 through 6. Run levels stop at six for practical and historical reasons, but it is entirely possible to have more if desired.

The following table summarises the UserLinux run levels:

 * 0            System Halt
 * 1            Single user
 * 2            Full multi-user mode (Default)
 * 3-5          Same as 2
 * 6            System Reboot

When run levels are discussed they are referred to as 'moving into', or 'going into' a certain run level. The inference is that you came from somewhere. With the exception of booting up, a system always transitions from one runlevel to another in response to certain conditions.

Special Run Levels

Run level 0 is the system halt condition. Nearly all modern X86 computers will power off automatically when run level 0 is reached. Older X86 computers, and various different architectures will remain powered on and display a message referring to the halt condition.

Run Level 1 is known as 'single user' mode. A more apt description would be 'rescue', or 'trouble-shooting' mode. In run level 1, no daemons (services) are started. Hopefully single user mode will allow you to fix whatever made the transition to rescue mode necessary.

(You can boot into single user mode typically by using your boot loader, lilo or grub, to add the word 'single' to the end of the kernel command line).

Run levels 2 through 5 are full multi-user mode and are the same in a default UserLinux (Debian) system. It is a common practise in other Linux distributions to use run level 3 for a text console login and run level 5 for a graphical login.

Run level 6 is used to signal system reboot. This is just like run level 0 except a reboot is issued at the end of the sequence instead of a power off.

In the interests of completeness, there is also a runlevel 'S' that the system uses on it's way to another runlevel. Read the man page for the init command ("man init") for more information, but you can safely skip this for all practical purposes.

Where Does a Run Level Live?

Like everything else in a Linux system, run levels are defined by files in the filesystem. All the run level files are found in the /etc directory according to the following table:

/etc/rc0.d              Run level 0
/etc/rc1.d              Run level 1
/etc/rc2.d              Run level 2
/etc/rc3.d              Run level 3
/etc/rc4.d              Run level 4
/etc/rc5.d              Run level 5
/etc/rc6.d              Run level 6

Notice a pattern? Each defined runlevel should have an rcX.d directory where X is the run level number. The contents of the rcX.d directory determines what happens at that run level.

(S)tart files, (K)ill files

Let's look at run level 2 since this is where we'll spend most of our time.

Here are the contents of a generic rc2.d directory:

S10sysklogd  S20cupsys   S20mailman  S20usermin  S91apache         S99xdm
S11klogd     S20exim4    S20makedev  S20xfs      S91apache2
S14ppp       S20fam      S20pcmcia   S20xprint   S99gdm
S18portmap   S20hylafax  S20samba    S89atd      S99rmnologin
S20acpid     S20inetd    S20ssh      S89cron     S99stop-bootlogd

At first glance the files in this directory look kind of intimidating. They should be. The files in the rcX.d directories are formatted for the computer to read, not the user.

Each file is a symbolic link to a script residing in the /etc/init.d directory and controls the starting, or stopping of a program, or daemon (service).

This is important enough to say again, each file is a symbolic link to a script and controls the starting, or stopping of a program, or daemon.

(If you wish to add your own startup script you can do so via the update-rc.d script)

In slightly modified man page format, here is how the files are named:

[K | S] + nn + [string] 

Working backwards, here is how the name parses out. The [string] is a human readable mnemonic for the executable file that is actually symbolically linked to. The 'nn' is a two digit number from 01-99; lower number programs are executed first. By this method, services that have a dependancy can be certain their precursor has ran. The K and S signify simply Kill, or Start.

When a system moves into a new runlevel, all the files that begin with S will be executed. When a system moves into a new runlevel all the files that begin with K will be executed. Yes, all the files will execute, but with one distinct difference: 'S' files invoke their program with the 'start' parameter, the 'K' files invoke their program with the 'stop' parameter. The UserLinux (Debian) system optimizes the runlevel change by not starting a daemon that is already running.

The simple elegance of this system is made possible by the alphabet. All the scripts will execute in alphabetical order. 'K' comes before 'S', so programs are stopped before they are started. Forgetting this fact can lead to a lot of chin scratching while manipulating your rcX.d files.

After the first letter comes the integer, again determining execution order. Finally, the mnemonic portion is followed alphabetically to determine execution order.

Let's look at some of the programs that are actually executed during a run level change:

S20exim4 -> ../init.d/exim4
S20fam -> ../init.d/fam
S20hylafax -> ../init.d/hylafax
S20inetd -> ../init.d/inetd
S20mailman -> ../init.d/mailman
S20makedev -> ../init.d/makedev
S20pcmcia -> ../init.d/pcmcia
S20samba -> ../init.d/samba
S20ssh -> ../init.d/ssh

All of these files have the same precedence as far as the system is concerned. They will be executed in the order listed, i.e. alphabetically.

All of the scripts that run during system start-up actually reside in the /etc/init.d/ directory, as suggested by the listing. The reasons for this are many, but basically boil down to common sense issues like: saving space, single point for editing, and everyone knowing where to find things.

Transitioning Between Run levels

When you leave a runlevel, nothing happens. All the action takes place when you enter the new run level.

Look at the following two rcX.d listings:


K01xdm      S18portmap S20fam     S20makedev S20usermin S89cron    S99rmnologin
S10sysklogd S20acpid   S20hylafax S20pcmcia  S20xfs     S91apache  S99stop-bootlogd
S11klogd    S20cupsys  S20inetd   S20samba   S20xprint  S91apache2 S99xdm
S14ppp      S20exim4   S20mailman S20ssh     S89atd     S99gdm


K01gdm       S20acpid    S20inetd    S20ssh      S89cron           S99xdm
S10sysklogd  S20cupsys   S20mailman  S20usermin  S91apache
S11klogd     S20exim4    S20makedev  S20xfs      S91apache2
S14ppp       S20fam      S20pcmcia   S20xprint   S99rmnologin
S18portmap   S20hylafax  S20samba    S89atd      S99stop-bootlogd

Look intensely at the two listings while allowing your eyes to unfocus. An image of a gnu will eventually appear. Ok, no it won't, but you believed for just a second, didn't you?

Look at the first listing, rc2.d. Notice the contradiction between the first program and the last program. K01xdm instructs the system to Kill xdm upon entering run level 2; S99xdm tells the system to start xdm. Who wins? Both programs are executed, but the last program to run will prevail. S99xdm, as it appears last in the alphabetical sequence, will leave xdm in a running state. The change to runlevel 2 was wasted typing.

Now, let's look closely at the rc3.d listing. The first thing that will be executed is the stopping of gdm, which is the default graphical display manager for UserLinux (Debian). Note the S99gdm file (symlink) has been removed. The purpose of the change is to move to a runlevel where everything else is still running, except the pretty window manager. This situation is called 'console mode'. As mentioned previously, many Linux distributions use run level 3 for console mode.

That's great, but how do I change run levels?

Before we change run levels it might help to find out which run level is current. Use the 'runlevel' command to tell you two things: The last run level, and the current run level. Here is the command and the output shown together due to the sparsity of the output:

ulsoho:/home/user1# runlevel
N 2

The 'N' stands for none, meaning there has been no run level change since powering up.

The init system controls run levels, but then again, the init system pretty much controls everything. The init system will be looked at in detail in a future article.

The primary command used to change run levels is 'telinit'. Get it? "Tell Init" to do something; like this:

telinit 3

telinit takes one argument on the command line. As always, see the man page for full details. Normally the argument will be one of: 0,1,2,3,4,5,6, or the letter 'S'. As you may have guessed, the numbers correspond to the run level you wish to move to. Using the 'S', for single-user, is the same as the number 1, but don't do it; the 'S' runlevel is intended for use by the UserLinux (Debian)system.

A note of caution is warranted here. You can easily use the telinit command to reboot (run level 6), or shutdown (run level 0) the system, but it is not recommended. Certain programs need special processing for an orderly shutdown. Bypassing the expected shutdown sequence can have dire effects on your data. Older _Unix_ systems are especially sensitive to shutdown/bootup operations

The preferred method for a serious runlevel change is 'shutdown'. There are easier mnemonics, but in a running system they all point to the 'shutdown' command. You can use the 'halt', or 'poweroff' command to stop a system and the 'reboot' command to restart your system. In each case they call the 'shutdown' command with different parameters.

(We've covered shutting down your Debian machine previously)

In a single system (non-networked, or no locally shared resources) environment, the shutdown choice is pretty much yours. However, in a multi-user production system the rule of thumb is learn the shutdown command. The two most basic uses of the 'shutdown' command are for halting, or rebooting. The important parameter to know for shutdown is WHEN is the action going to occur. Here is the command synopsis from the shutdown man page:

/sbin/shutdown [-t sec] [-arkhncfFHP] time [warning-message]

The vast majority of your shutdowns will follow one of these two forms:

shutdown -h now

or to reboot instead of halt:

shutdown -r now

Intuitively, the arguments mean 'halt' and 'reboot', respectively.

In a multi-user system like a file server, the most important parameter is 'time'. The time can be an actual clock time in the form of HH:MM, or a Julian style shutdown X minutes from now, denoted by the +X syntax. Note that the '+' is needed. The keyword 'now' is synonymous with '+0'. Here are two examples using the time parameter:

shutdown -h 16:30
shutdown -r +10

Another important point to remember: once the shutdown command is issued, a notice is sent to all the users of the system and no further logins are allowed. For example, if you need to bring the system down at midnight, don't issue the shutdown command at noon and leave to take a nap. No new users will be able to login for the next 12 hours.

A good admin never takes a system down without warning the user community, but the shutdown notice is only sent after the command is executed! Fortunately, there are two ways around the downtime notification dilemma. The first is the 'motd', Message Of The Day. The motd is a useful feature that is often overlooked. Using the motd is easy and you are urged to read the simple man page for details. The second method of notification is the -k option. Using -k will send the downtime notice to all the users, but will not actually start the shutdown sequence. There is an important limitation to the shutdown notification: the downtime message is only sent 15 minutes (or less) prior to the actual shutdown.

The warning-message parameter may be useful for...high maintenance users. I find that the default message is authoritative and simple enough to accomplish the task.

Troubleshooting in Run Levels

Here is a tip contributed by Nicholas Petreley. Sometimes you may not want all the programs in a run level to execute. In this situation an easy way to disable a program is to rename it with the initial S, or K in lowercase. The system will ignore all programs that do not begin with a capital S, or K.

This article was originally written as part of a course for UserLinux system administration. It initially appeared on the UserLinux wiki here. The wiki version, as a living document, may have more, or less to offer in the way of content.

(UserLinux is a subset of Debian. Everywhere 'UserLinux' appears, you can substitute 'Debian' with equal facility.)



Re: An introduction to run-levels
Posted by grimoire (82.69.xx.xx) on Mon 15 Aug 2005 at 14:22
It's worth noting that there's rarely any actual need to mess around with runlevels; from doing Debian support on IRC, I know that 99% of occasions where people think they need to play with them, they've got the wrong end of the stick.

Readers may also want to familiarise themselves with the invoke-rc.d and update-rc.d scripts if they are going to manipulate startup scripts.

[ Parent ]

Re: An introduction to run-levels
Posted by Anonymous (195.212.xx.xx) on Mon 15 Aug 2005 at 14:47
runlevels are useful for a couple of things:
  • correct boot order of specific processes, e.g. pcmcia
  • switch to runlevel 1 for upgrades modifying X or other important infrastructure tools, stopping all non-essential processes to avoid problems

[ Parent ]

Re: An introduction to run-levels
Posted by redsolo (85.224.xx.xx) on Tue 20 Sep 2005 at 21:37
Just to clarify, if Im building a media box with the only feature to bring up freevo (and X11), should I mess with runlevels, and set it to 1 upon boot? Or is it meaningless

[ Parent ]

Re: An introduction to run-levels
Posted by Anonymous (200.158.xx.xx) on Sun 6 Nov 2005 at 10:33
The text didn't talk about the most important thing about Debian runlevels, for me, that is HOW DO I BOOT IN TEXT MODE IN DEBIAN??? By the text, runlevels 2-6 are all the same. It mention that runlevel 3 is used in other distributions as a text console boot, but it do not mention how to do it in Debian. As far as I know, just Debian has this different runlevel configuration, so the most important think in a runlevel text, for debian, is to tell people how to configure the runlevels in Debian like we could configure it in other linuxs... It's really a pitty, 'coz it didn't help me. Not even the debian page talk about it. SO, now I don't know how I'll be able to install my nvidia driver. The X window cannot load to do the nvidia instalation. That's it. Hope someone put it here to make this text really useful to people, because pretty much all that it has now (important stuff) is found in the debian page. Not really anything new.

[ Parent ]

Re: An introduction to run-levels
Posted by Anonymous (84.144.xx.xx) on Mon 7 Nov 2005 at 10:27
It seems like we share our problems...

Did I get this right? I only need to edit the rcX.d file (after backing it up) to set up my "own" runlevels und then telinit to the changed level?

[ Parent ]

Re: An introduction to run-levels
Posted by Anonymous (203.132.xx.xx) on Wed 9 Nov 2005 at 21:23

First of all, you want to find out what is starting X11 on your system. Most likely it's a display manager like xdm, kdm or gdm. When you first boot up, look at the welcome screen and you should be able to tell if its kdm (KDE), gdm (Gnome), or xdm (X11).

To make sure you chose the correct display manager, run this command:

cat /etc/X11/default-display-manager
Mine says "/usr/bin/kdm". Yours could be different. (You can edit /etc/X11/default-display-manager to change the display manager if you want to.)

So run commands like this:

ls -la /etc/rc*d/*kdm*
ls -la /etc/rc*d/*gdm*
ls -la /etc/rc*d/*xdm*

That will produce results something like this. I'm looking at kdm here, because that's the one I'm using.

lrwxrwxrwx  1 root root 13 Feb 14  2005 /etc/rc0.d/K01kdm -> ../init.d/kdm
lrwxrwxrwx  1 root root 13 Feb 14  2005 /etc/rc1.d/K01kdm -> ../init.d/kdm
lrwxrwxrwx  1 root root 13 Feb 14  2005 /etc/rc2.d/S99kdm -> ../init.d/kdm
lrwxrwxrwx  1 root root 13 Feb 14  2005 /etc/rc3.d/S99kdm -> ../init.d/kdm
lrwxrwxrwx  1 root root 13 Feb 14  2005 /etc/rc4.d/S99kdm -> ../init.d/kdm
lrwxrwxrwx  1 root root 13 Feb 14  2005 /etc/rc5.d/S99kdm -> ../init.d/kdm
lrwxrwxrwx  1 root root 13 Feb 14  2005 /etc/rc6.d/K01kdm -> ../init.d/kdm

Now what this means is that kdm starts in runlevels 2, 3, 4, and 5. kdm is stopped in runlevels 0, 1, and 6. If you want runlevel 3 to be text only in your system, you should be able to simply change the link for runlevel 3 for your display manager from start (S) to kill (K). So for example you could try this:

  mv /etc/rc3.d/S99kdm /etc/rc3.d/K01kdm

Then use the telinit command to change to runlevel 3:

   telinit 3

If you wanted runlevel 3 to be the default, then you need to edit /etc/inittab.

# The default runlevel.
You'd change the '2' to a '3'. Next time you reboot, your system will start in runlevel 3. There will be no display manager running in runlevel 3, because you turned it off. Therefore, runlevel 3 will become text only, and it will be the default. If that's what you want to do.

[ Parent ]

Re: An introduction to run-levels
Posted by Anonymous (61.95.xx.xx) on Fri 23 Dec 2005 at 11:41
I tried this in my system. That is I renamed S99gdm as K01gdm (gdm in my case). When I rebooted it, GNOME login did not open as expected. But even the console login prompt did not come. It was simply blank. I went back in the recovery mode and fixed it back as S99gdm. Now, how can I get that console login prompt? Do I need to include some other shell script in that directory?

[ Parent ]

Re: An introduction to run-levels
Posted by Anonymous (132.174.xx.xx) on Mon 13 Feb 2006 at 16:12
sounds like you're trying to do what I am doing on my Kubuntu system. I want the runlevels to work sort of like RedHat, although in general I like Debian better. I want this:

1 - single user, Kubuntu defaults
2 - single user with sshd so I can remote admin
3 - console only multiuser like RedHat (not that I'd use this on my laptop much, but I like having this option in general for UNIX operating systems
4 - unused, just going to leave it Kubuntu defaults like Kubuntu rc2.d or my rc5.d
5 - multiuser with X Windows and KDE, the Kubuntu defaults

First I edited /etc/inittab and changed the default runlevel to 5 for my laptop

Then cp -l /etc/rc1.d/ /etc/rc2.d/ and cp -l /etc/rc3.d/ /etc/rc2.d and then delete all the links I don't want to make everything killed and only start sshd first (S15ssh) and then single user (S20single). This might not work because I'm just hacking around, but if not I'll figure out which one is the text logon that would be used if you switched this in the system properties with wahtever K tool does this (I know I've been there before).

Really, you have to expect this to be difficult when you're making runlevels work different on your system. This is not easy. I did this once on a RedHat system just to screw around and it worked great though. I can't remember what I was doing but it was probably making use of runlevel 4 on that system.

I also like a previous poster's suggestion to mv things to change S##service to K##service; it's a lot faster than what I'm doing for most things you'd want to change. Bottom line, know this:

The K scripts in order kill things. The S scripts in order start things. Know what you're killing. Know what you're starting. And leave yourself a couple untouched run levels in case you screw something up; I haven't changed single user, 4 or 5, so I can telinit 5 if everything is wrong and I can always start over by copying rc5.d to another run level. Don't mess with single user and leave one other unchanged, adn experiment.

as soon as Adept finishes upgrading packages I'm going to try this out. i'll post results.

[ Parent ]

Are you sure 'K' is for 'kill' and 'S' is for '
Posted by Anonymous (98.125.xx.xx) on Wed 20 Aug 2014 at 01:40
Are you sure 'K' is for 'kill' and 'S' is for 'start'? Because on my default install of Ubuntu it has all the mounting and startup scripts running as K numbers and the umount and stop scripts are all running as 'S' numbers which is backwards from what you are indicating...

For example on mine it's: S60umountroot and S90halt

and: K20zfs-mount

[ Parent ]

Re: An introduction to run-levels
Posted by Anonymous (65.241.xx.xx) on Wed 15 Feb 2006 at 01:04
Actually the example cited is exactly that: disabling the window manager in runlevel 2.

[ Parent ]

Re: An introduction to run-levels (Debian Booting in text!!)
Posted by Anonymous (161.109.xx.xx) on Tue 28 Mar 2006 at 19:15
This worked for me. Go to /etc/rc3.d/ there you should find your gui log in mine was gnome so it was S99gdm. For testing purposes move S99gdm to a temp file somewhere like your home dir. Change your inittab located (/etc/inittab) to read something like this

# The default runlevel.

write it the save, restart. This worked for me should you to I am running Debian 3.1_r1 i386. However if this fails to work during boot it will ask for the root password for you to fix all you have to do is move S99gdm (in my case) back to the rc3.d folder. I have tried this on the first run level (1) and it didnt work but the third runlevel works. Good luck!

[ Parent ]

Re: An introduction to run-levels
Posted by Anonymous (132.174.xx.xx) on Tue 14 Feb 2006 at 15:43
well here i am the overachiever. here's what I did:

First, I got rid of something stupid i did, I had put S20single in rc2.d . Duh. Right after S15ssh . So then I read /etc/init.d/single and found out that it kills all other processes to enter single user mode. So don't do this! ;) I was remoting my lappy from work, and guess what, telinit 2 ended my experiment until I could get home last night. Got home late, just rebooted, and I'm finishing up this mroning.

So here's the real deal:
1 - single user
2 - I wanted single-user with sshd, but I have to log in as a user for ssh because I don't like letting the security hole of root logging in directly from remote. So this runlevel is multiuser, barely, for remote administration when I want to unmount everything. (yeah, I'm sshing into a user account so technically I need /home/username mounted . . . . I'll have to create /home/username when the /home partition is unmounted and then just mount over that temporary home dir for normal use, easy workaround)
3 - multiuser, just like Red Hat
4 - multiuser and X on VNC for remote control when I'm behind my firewall and I want to remote control my laptop from work. I don't really want X running on console, not that it matters.
5 - multiuser with X on console and no VNC for "normal use". (This should not leave stupid security holes like VNC for when I'm in a coffee shop etc.)

I changed a line in /etc/inittab to change the default run level to 5.

I created /etc/init.d/vncserver to start and stop this new service, using the scripts already in that directory to model:

root@hostname:~# cat /etc/init.d/vncserver
#! /bin/sh
# /etc/init.d/vncserver: Start and stop the vncserver daemon


test -f $DAEMON || exit 0

set -e

. /lib/lsb/init-functions

case "$1" in
log_begin_msg "Starting vncserver daemon . . . "
start-stop-daemon --start --quiet --pidfile $PIDFILE --exec $DAEMON || log_end_msg 1
log_end_msg 0
log_begin_msg "Stopping vncserver daemon . . . "
start-stop-daemon --stop --quiet --oknodo --pidfile $PIDFILE || log_end_msg 1
log_end_msg 0

log_begin_msg "Restarting vncserver daemon . . . "
start-stop-daemon --stop --quiet --oknodo --retry 30 --pidfile $PIDFILE
start-stop-daemon --start --quiet --pidfile $PIDFILE --exec $DAEMON || log_end_msg 1
log_end_msg 0

log_success_msg "Usage: /etc/init.d/vncserver {start|stop|restart}"
exit 1

exit 0

I tested the script by running it like
# /etc/init.d/vncserver start
# /etc/init.d/vncserver stop
and it ran fine, so then to make the links:

root@hostname:~# ln -s /etc/init.d/vncserver /etc/rc1.d/K01vncserver
root@hostname:~# ln -s /etc/init.d/vncserver /etc/rc2.d/K01vncserver
root@hostname:~# ln -s /etc/init.d/vncserver /etc/rc3.d/K01vncserver
root@hostname:~# ln -s /etc/init.d/vncserver /etc/rc5.d/K01vncserver
root@hostname:~# ls /etc/rc4.d
S05vbesave S14ppp S20makedev S21kdm S89cron S99stop-bootlogd
S10acpid S19cupsys S20pcmcia S25bluez-utils S98usplash
S10sysklogd S19hplip S20powernowd S25mdadm S99acpi-support
S11klogd S20apmd S20rsync S89anacron S99fetchmail
S12dbus S20hotkey-setup S20ssh S89atd S99rmnologin
root@hostname:~# ln -s /etc/init.d/vncserver /etc/rc4.d/S23vncserver

The links run in order, first the kills then the starts, so I decided to put it after kdm. I might decide to get rid of kdm there so I would do this:
# mv /etc/rc4.d/S21kdm /etc/rc4.d/K01kdm
I'm not sure if that will work or not until I'm sitting in front of the laptop so I can't test this morning. But I can test just about everything except what's going on with the local console from remote. Probably I could test that enough from remote as well if I get creative with various tools and do some logical deduction. But it's easier to sit down tonight ;)

I also changed the rc2.d and rc3.d scripts a bit to accomplish my goal of starting the graphical desktop or not, etc; there's what I've got:

root@hostname:~# ls /etc/rc*.d

K01kdm K11cron K19hplip K20makedev K20ssh K86ppp S20single
K01usplash K12dbus K20acpi-support K20pcmcia K21acpid K89atd
K01vncserver K15fetchmail K20apmd K20powernowd K25mdadm K89klogd
K11anacron K19cupsys K20hotkey-setup K20rsync K74bluez-utils K90sysklogd

K01kdm K12dbus K20apmd K21acpid K89klogd S99stop-bootlogd
K01usplash K15fetchmail K20hotkey-setup K25mdadm K90sysklogd
K01vncserver K19cupsys K20pcmcia K74bluez-utils S15ssh
K11anacron K19hplip K20powernowd K86ppp S20makedev
K11cron K20acpi-support K20rsync K89atd S99rmnologin

K01kdm S11klogd S20apmd S20rsync S89atd S99rmnologin
K01vncserver S12dbus S20hotkey-setup S20ssh S89cron S99stop-bootlogd
S05vbesave S14ppp S20makedev S25bluez-utils S98usplash
S10acpid S19cupsys S20pcmcia S25mdadm S99acpi-support
S10sysklogd S19hplip S20powernowd S89anacron S99fetchmail

S05vbesave S14ppp S20makedev S21kdm S89atd S99rmnologin
S10acpid S19cupsys S20pcmcia S23vncserver S89cron S99stop-bootlogd
S10sysklogd S19hplip S20powernowd S25bluez-utils S98usplash
S11klogd S20apmd S20rsync S25mdadm S99acpi-support
S12dbus S20hotkey-setup S20ssh S89anacron S99fetchmail

K01vncserver S12dbus S20hotkey-setup S20ssh S89atd S99rmnologin
S05vbesave S14ppp S20makedev S21kdm S89cron S99stop-bootlogd
S10acpid S19cupsys S20pcmcia S25bluez-utils S98usplash
S10sysklogd S19hplip S20powernowd S25mdadm S99acpi-support
S11klogd S20apmd S20rsync S89anacron S99fetchmail

IMPORTANT NOTE: change these runlevels at your own peril. Especially DO NOT CHANGE rc0.d rc1.d rcS.d or rc6.d unless you REALLY REALLY know what you're doing, and leave yourself a backup someplace; for instance I left rc5.d untouched even after all my heavy modifications, so if I really screw up I can always boot to either level 5 or single user and then copy the rc5.d scripts over whatever runlevel I hopelessly screwed up.

root@hostname:~# telinit 2
root@hostname:~# runlevel
3 2

As you can see I was in runlevel 3 previously when I was making edits. Now I'm in runlevel 2.

root@hostname:~# ps aux
root 1 0.0 0.0 1560 536 ? S 09:59 0:01 init [2]
root 6689 0.0 0.1 3540 1540 ? Ss 10:00 0:00 /usr/sbin/sshd
root 7040 0.0 0.0 0 0 ? S< 10:00 0:00 [krfcommd]
root 7134 0.0 0.0 1560 496 tty1 Ss+ 10:00 0:00 /sbin/getty 38400 tty1
root 7208 0.0 0.2 6264 1892 ? Ss 10:02 0:00 sshd: username [priv]
username 7210 0.0 0.2 6264 1988 ? R 10:02 0:00 sshd: username@pts/0
username 7211 0.0 0.2 4672 2080 pts/0 Ss 10:02 0:00 -bash
root 7323 0.0 0.1 3432 972 pts/0 S 10:09 0:00 su -
root 7324 0.0 0.2 2752 1628 pts/0 R 10:09 0:00 -su
root 7408 0.0 0.0 1556 488 tty2 Ss+ 10:26 0:00 /sbin/getty 38400 tty2
root 7411 0.0 0.0 1556 492 tty3 Ss+ 10:26 0:00 /sbin/getty 38400 tty3
root 7414 0.0 0.0 1560 492 tty4 Ss+ 10:26 0:00 /sbin/getty 38400 tty4
root 7417 0.0 0.0 1556 492 tty5 Ss+ 10:26 0:00 /sbin/getty 38400 tty5
root 7420 0.0 0.0 1560 496 tty6 Ss+ 10:26 0:00 /sbin/getty 38400 tty6
root 7986 0.0 0.1 2552 876 pts/0 R+ 10:27 0:00 ps aux

so far so good; the console will allow logins with /sbin/getty, X windows is not running, and sshd is still running (or I wouldn't still be connected!)

I do telinit 3 and it starts bluetooth, pcmcia, etc and it's a full system but without X windows; console only just like I wanted. telinit 5 also works just fine and is the default for Kubuntu, x windows runs, the console takes logons, sshd runs, and the vnc server doesn't start.

ahem. I seem to have a problem with runlevel 4. It runs, everything goes well, EXCEPT that my rc script to start the vncserver never finishes running. the vncserver starts and accepts connections, but obviously I did something wrong.

root 8540 0.0 0.1 2608 1324 ? Ss 10:30 0:00 /bin/sh /etc/init.d/rc 4
root 8547 0.0 0.0 2588 748 ? Ss 10:30 0:00 /usr/bin/kdm
root 8550 3.1 1.5 13544 11932 ? S 10:30 0:04 /usr/X11R6/bin/X -br -nolisten tc
root 8551 0.0 0.1 2868 1136 ? S 10:30 0:00 -:0
root 8552 0.0 0.1 2644 1328 ? S 10:30 0:00 /bin/sh /etc/rc4.d/S23vncserver s
root 8564 0.0 0.3 4252 2540 ? S 10:30 0:00 /usr/bin/perl /usr/bin/vncserver
root 8568 0.0 0.2 3832 2136 ? S 10:30 0:00 /usr/bin/perl /usr/bin/vncpasswd
root 8569 0.0 0.0 1544 360 ? S 10:30 0:00 /usr/bin/realvncpasswd.real //.vn
root 8572 2.0 2.2 27716 17800 ? S 10:30 0:02 /usr/bin/kdm_greet
root 8577 0.0 0.1 2548 876 pts/0 R+ 10:32 0:00 ps aux

This is for another day, but this should be enough to tell people on thsi forum how to use runlevels. Just be careful! And keep backups! UNIX is beautiful once you get under the hood a little bit. Learn UNIX and any linux or BSD operating system is rediculously easy, far easier than spelling rideculously correctly ;)

if you are curious drop by www_urnotalone_com/dosadi sometime, although that's NOT UNIX!!!!!

[ Parent ]

Re: An introduction to run-levels
Posted by Anonymous (193.92.xx.xx) on Fri 12 May 2006 at 02:10
Why isn't there an easy ncurse utility for managing services like red hat's ntsysv?
I've switched over debian resently and I spent a lot of time searching for an easy way to deactivating the services on startup at the end I was convinced that there is no easy way and I had to do the renaming.

Anyway I found Debian much better than Red Hat (I used fc3 and red hat 9) on my file servers. apt-get rocks and this pages helped me a lot.


[ Parent ]

Re: An introduction to run-levels
Posted by Anonymous (84.161.xx.xx) on Sat 10 Jun 2006 at 19:14
> Why isn't there an easy ncurse utility for managing services like red hat's ntsysv?

There is, it is called sysv-rc-conf.

[ Parent ]

Re: An introduction to run-levels
Posted by Anonymous (125.22.xx.xx) on Tue 20 Jun 2006 at 20:33

[ Parent ]

Roll it yourself?
Posted by Anonymous (192.94.xx.xx) on Thu 21 May 2009 at 02:48
It's funny that the author mentions the fact that other Linuxes use runlevel to start and stop X11 - but fails to explain the Debian approach. Debian users have to tailor their own non-gui mode?!? Seems like an uncessary pain.

[ Parent ]

Re: An introduction to run-levels
Posted by Anonymous (58.177.xx.xx) on Sat 5 Jan 2013 at 02:12
Regardless of wether it is a 'K' or 'S', the 'stop' command is always given to files in runlevels 0 and 6.

[ Parent ]

You're right on this...
Posted by Anonymous (98.125.xx.xx) on Wed 20 Aug 2014 at 01:53
Yeah I think your right because in mine which is Ubuntu, I see all the S ones are like S60umountroot and S90halt, and there is a K20zfs-mount one in there too but it has a stop command in it so it is for both..

This is good to know stuff, because I wasn't sure. My question now though, becomes, what order does it run the stop between the S's and the K's within those run levels. Is it alpha-numeric, or just numeric, ignoring the S or K?

[ Parent ]

Re: An introduction to run-levels
Posted by Anonymous (101.60.xx.xx) on Thu 25 Jun 2015 at 07:04
Important Note: "string" in "[K | S] + nn + [string]" must be lowercase. The script won't be executed if it name is uppercase.

[ Parent ]

Re: An introduction to run-levels
Posted by Anonymous (115.114.xx.xx) on Thu 19 Nov 2015 at 08:57
How can I run a script at the shutdown ?
I need to make a curl call so I need the network up. This means that I need to run the script when I switch from run level 3 to run level 0. How can this be achieved ?

[ Parent ]