From Annvix

System startup and shutdown

Traditionally, there have been two startup and shutdown schemes that handle booting and shutting down UNIX systems: the BSD scheme and the "System V" scheme. Most Linux distributions use the "System V" (or SysV) scheme. Annvix uses a unique method to startup and shutdown the system. This system, also known as the "init" system, is a hybrid system based on Gentoo's init system and Mandriva's init system. Unlike either Gentoo or Mandriva, Annvix uses runit to manage everything.

A typical Linux system uses SysVinit, which is based on the SysV scheme and is made up of a set of scripts that setup the system, mount filesystems, and in turn call a number of other scripts (called initscripts) that start services. These initscripts can be called independently to start and stop individual services. At system shutdown, these scripts shutdown all running services, unmount filesystems, and then halt or reboot the system.

Annvix, using runit, starts and stops services with run scripts, rather than initscripts. Initscripts are still used for one-time services and non-daemon services, such as setting up the firewall, calling kudzu to detect hardware, starting the network, etc.

The SysV init scheme calls for the use of "runlevels". When the Linux kernel boots, it mounts the root filesystem and then typically executes a script called rc.sysinit which sets up the basic system configuration and usually checks the filesystems. It then calls a script called rc with an argument; this argument is the runlevel to execute. Different Linux distributions may use a variation of the following, but this is by-and-large a typical runlevel scheme:

• 0: complete machine stop
• 1: single-user mode
• 2: multi-user mode
• 3: multi-user mode, with networking
• 4: unused
• 5: similar to runlevel 3, but starts the graphical login interface, for use with X
• 6: restart

Annvix does not use numbered runlevels. Instead, Annvix uses named runlevels which allow for much more customization, although it shouldn't really be necessary to change the defaults. Annvix comes with the following named runlevels:

• default: multi-user mode, with networking
• single: multi-user mode, without networking and no services starting (other than cron, mingetty, and socklog)

The Boot Scripts

To get a more intimate look at how Annvix boots, this section describes the boot process in detail. When the bootloader executes the kernel to load, it also uncompresses a ramdisk image, which contains (among other things) modules to load in order to mount the root filesystem and a script called linuxrc which creates some temporary partitions, mounts required filesystems, and so forth. Once this script is done, and the root filesystem is mounted, it executes /sbin/init, which is provided by the runit package. init is the first process of any Linux system, and with runit, if init is the first process, it replaces itself with /sbin/runit(8) which then executes the script /etc/runit/1 to start "stage 1". Runit operates in three stages:

• 1: one-time startup tasks
• 2: the normal operating system; if this stage exits abnormally it will be restarted
• 3: halt/reboot

One stage 1 is started by executing /etc/runit/1, that script then executes /sbin/rc with a single argument: 1. This argument tells rc that the system is starting; an argument of 0 would tell rc that the system is shutting down. The rc script does all the heavy lifting of mounting other filesystems, performing filesystem checks, loading kernel modules to interact with different hardware devices, and so forth. The rc script also calls the traditional "initscripts" found in the runlevel's definition directory: /etc/runlevels/default for the "default" runlevel. When rc exits and control is passed back to the stage 1 script, stage 1 completes and stage 2 begins.

Stage 2, which is executed by /etc/runit/2, starts the supervised services found in the runlevel's service directory: /etc/runlevels/default/service for the "default" runlevel. Each runlevel has it's own service directory; the rc script sets /service as a symlink to the runlevels service directory at boot.

Stage 3 is called when a superuser calls the halt(8), reboot(8), or shutdown(8) commands. This will exit stage 2 and call /etc/runit/3, which signals runit to shutdown all supervised services and then calls the rc script with the single argument '0'.

Managing Initscripts with rc-update

Traditional Linux distributions will use programs like service to start/stop and otherwise manage services (Annvix uses srv(8)), and chkconfig to add or remove services from a particular runlevel. Annvix does not use chkconfig because chkconfig is very much tied to number-based runlevels. Instead, Annvix uses a modified version of Gentoo's rc-update script.

To see what initscripts are called for each runlevel, you can look in /etc/runlevels/[runlevel] or use rc-update:

# rc-update -s       
            apparmor | default        
            iptables | default
            keytable | default        
             kheader | default        
               kudzu | default        
               netfs | default        
             network | default        
            rc.local | default single

Here you can see that the initscript /etc/init.d/rc.local is to be called in both runlevels "default" and "single" and the rest of the supplied initscripts are executed only in the "default" runlevel.

To add an initscript to a runlevel, use the "add" command:

# rc-update add iptables single
iptables added to runlevel single

This command, as illustrated, adds the /etc/init.d/iptables initscript to the "single" runlevel. This can also be seen by now looking in /etc/runlevels/single/:

# ls -al /etc/runlevels/single/
total 4
drwxr-x--- 3 root admin   54 Mar  5 23:47 .
drwxr-xr-x 4 root root    33 Mar 30  2007 ..
lrwxrwxrwx 1 root root    20 Mar  5 23:43 03iptables -> /etc/init.d/iptables
lrwxrwxrwx 1 root root    20 Mar  5 23:47 99rc.local -> /etc/init.d/rc.local
drwxr-x--- 2 root admin 4096 Dec 29 21:32 service

To remove an initscript from some runlevel, use the "del" command:

# rc-update del iptables single
'iptables' removed from the following runlevels: single

Looking at the runlevel directory, you'll note the symlink with a numbered prefix. Somewhat similar to SysVinit, Annvix uses this to order which scripts are executed. For instance, on a SysV system, you might see:

$ ls -l /etc/rc.d/rc3.d/
total 0
lrwxrwxrwx  1 root root 20 Jan  2  2007 K66messagebus -> ../init.d/messagebus*
lrwxrwxrwx  1 root root 19 Jan  2  2007 K68rpcidmapd -> ../init.d/rpcidmapd*
lrwxrwxrwx  1 root root 17 Jan  2  2007 K69rpcgssd -> ../init.d/rpcgssd*
lrwxrwxrwx  1 root root 20 Jan  2  2007 K69rpcsvcgssd -> ../init.d/rpcsvcgssd*
lrwxrwxrwx  1 root root 16 Jan  2  2007 K72autofs -> ../init.d/autofs*
lrwxrwxrwx  1 root root 19 Jan  2  2007 K95harddrake -> ../init.d/harddrake*
lrwxrwxrwx  1 root root 18 Jan  2  2007 S03iptables -> ../init.d/iptables*
lrwxrwxrwx  1 root root 14 Jan  2  2007 S04acpi -> ../init.d/acpi*
lrwxrwxrwx  1 root root 17 Jan  2  2007 S10network -> ../init.d/network*
lrwxrwxrwx  1 root root 17 Jan  2  2007 S11portmap -> ../init.d/portmap*
lrwxrwxrwx  1 root root 16 Jan  2  2007 S12syslog -> ../init.d/syslog*
lrwxrwxrwx  1 root root 17 Jan  2  2007 S13partmon -> ../init.d/partmon*
lrwxrwxrwx  1 root root 15 Jan  2  2007 S14acpid -> ../init.d/acpid*
lrwxrwxrwx  1 root root 17 Jan  2  2007 S14nfslock -> ../init.d/nfslock*
lrwxrwxrwx  1 root root 15 Jan  2  2007 S25netfs -> ../init.d/netfs*
lrwxrwxrwx  1 root root 17 Jan  2  2007 S29numlock -> ../init.d/numlock*
lrwxrwxrwx  1 root root 14 Sep 12 23:01 S30nscd -> ../init.d/nscd*
lrwxrwxrwx  1 root root 13 Jan  2  2007 S40atd -> ../init.d/atd*
lrwxrwxrwx  1 root root 16 Jan  2  2007 S40smartd -> ../init.d/smartd*
lrwxrwxrwx  1 root root 14 Dec 19 10:45 S55sshd -> ../init.d/sshd*
lrwxrwxrwx  1 root root 14 Jan  2  2007 S56ntpd -> ../init.d/ntpd*
lrwxrwxrwx  1 root root 20 Jan  2  2007 S56rawdevices -> ../init.d/rawdevices*
lrwxrwxrwx  1 root root 13 Jan  2  2007 S60nfs -> ../init.d/nfs*
lrwxrwxrwx  1 root root 18 Jan  2  2007 S75keytable -> ../init.d/keytable*
lrwxrwxrwx  1 root root 17 Mar 10  2007 S80postfix -> ../init.d/postfix*
lrwxrwxrwx  1 root root 17 Sep  6 18:25 S85proftpd -> ../init.d/proftpd*
lrwxrwxrwx  1 root root 15 Jan  2  2007 S90crond -> ../init.d/crond*
lrwxrwxrwx  1 root root 17 Jan  2  2007 S95kheader -> ../init.d/kheader*
lrwxrwxrwx  1 root root 11 Jan  2  2007 S99local -> ../rc.local*

Notice that each script can have a different prefix; the S prefix is for Start and the K prefix is for Kill -- in relation to the service. In this way, services are ordered in how the start and stop. Annvix only concerns itself with how services are started, and calls stop for the initscripts in alphabetical order. Because Annvix does not handle or support changing runlevels "on the fly" there is no need to be concerned with ordered stops, so Annvix does not use a lettered/numeric prefix as other Linux distributions.

One thing to note is that if the special "stop" initscript exists, it will be executed before any other initscripts are called. This script is called /etc/init.d/rc.local-stop, and is a counterpart to /etc/init.d/rc.local which is only executed on start (and never executed on stop). Therefore, if you start something in rc.local and you want to ensure a clean shutdown, use rc.local-stop to stop it or do whatever cleanup is required.

• This page was last modified 01:03, 6 March 2008.
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