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F.2.4. The /sbin/init Program
/sbin/initprogram (also called
init) coordinates the rest of the boot process and configures the environment for the user.
initcommand starts, it becomes the parent or grandparent of all of the processes that start up automatically on the system. First, it runs the
/etc/rc.d/rc.sysinitscript, which sets the environment path, starts swap, checks the file systems, and executes all other steps required for system initialization. For example, most systems use a clock, so
/etc/sysconfig/clockconfiguration file to initialize the hardware clock. Another example is if there are special serial port processes which must be initialized,
initcommand then processes the jobs in the
/etc/event.ddirectory, which describe how the system should be set up in each SysV init runlevel. Runlevels are a state, or mode, defined by the services listed in the SysV
/etc/rc.d/rc<x>.d/directory, where <x> is the number of the runlevel. For more information on SysV init runlevels, refer to Section F.4, “SysV Init Runlevels”.
initcommand sets the source function library,
/etc/rc.d/init.d/functions, for the system, which configures how to start, kill, and determine the PID of a program.
initprogram starts all of the background processes by looking in the appropriate
rcdirectory for the runlevel specified as the default in
rcdirectories are numbered to correspond to the runlevel they represent. For instance,
/etc/rc.d/rc5.d/is the directory for runlevel 5.
When booting to runlevel 5, the
initprogram looks in the
/etc/rc.d/rc5.d/directory to determine which processes to start and stop.
Below is an example listing of the
K05innd -> ../init.d/innd K05saslauthd -> ../init.d/saslauthd K10dc_server -> ../init.d/dc_server K10psacct -> ../init.d/psacct K10radiusd -> ../init.d/radiusd K12dc_client -> ../init.d/dc_client K12FreeWnn -> ../init.d/FreeWnn K12mailman -> ../init.d/mailman K12mysqld -> ../init.d/mysqld K15httpd -> ../init.d/httpd K20netdump-server -> ../init.d/netdump-server K20rstatd -> ../init.d/rstatd K20rusersd -> ../init.d/rusersd K20rwhod -> ../init.d/rwhod K24irda -> ../init.d/irda K25squid -> ../init.d/squid K28amd -> ../init.d/amd K30spamassassin -> ../init.d/spamassassin K34dhcrelay -> ../init.d/dhcrelay K34yppasswdd -> ../init.d/yppasswdd K35dhcpd -> ../init.d/dhcpd K35smb -> ../init.d/smb K35vncserver -> ../init.d/vncserver K36lisa -> ../init.d/lisa K45arpwatch -> ../init.d/arpwatch K45named -> ../init.d/named K46radvd -> ../init.d/radvd K50netdump -> ../init.d/netdump K50snmpd -> ../init.d/snmpd K50snmptrapd -> ../init.d/snmptrapd K50tux -> ../init.d/tux K50vsftpd -> ../init.d/vsftpd K54dovecot -> ../init.d/dovecot K61ldap -> ../init.d/ldap K65kadmin -> ../init.d/kadmin K65kprop -> ../init.d/kprop K65krb524 -> ../init.d/krb524 K65krb5kdc -> ../init.d/krb5kdc K70aep1000 -> ../init.d/aep1000 K70bcm5820 -> ../init.d/bcm5820 K74ypserv -> ../init.d/ypserv K74ypxfrd -> ../init.d/ypxfrd K85mdmpd -> ../init.d/mdmpd K89netplugd -> ../init.d/netplugd K99microcode_ctl -> ../init.d/microcode_ctl S04readahead_early -> ../init.d/readahead_early S05kudzu -> ../init.d/kudzu S06cpuspeed -> ../init.d/cpuspeed S08ip6tables -> ../init.d/ip6tables S08iptables -> ../init.d/iptables S09isdn -> ../init.d/isdn S10network -> ../init.d/network S12syslog -> ../init.d/syslog S13irqbalance -> ../init.d/irqbalance S13portmap -> ../init.d/portmap S15mdmonitor -> ../init.d/mdmonitor S15zebra -> ../init.d/zebra S16bgpd -> ../init.d/bgpd S16ospf6d -> ../init.d/ospf6d S16ospfd -> ../init.d/ospfd S16ripd -> ../init.d/ripd S16ripngd -> ../init.d/ripngd S20random -> ../init.d/random S24pcmcia -> ../init.d/pcmcia S25netfs -> ../init.d/netfs S26apmd -> ../init.d/apmd S27ypbind -> ../init.d/ypbind S28autofs -> ../init.d/autofs S40smartd -> ../init.d/smartd S44acpid -> ../init.d/acpid S54hpoj -> ../init.d/hpoj S55cups -> ../init.d/cups S55sshd -> ../init.d/sshd S56rawdevices -> ../init.d/rawdevices S56xinetd -> ../init.d/xinetd S58ntpd -> ../init.d/ntpd S75postgresql -> ../init.d/postgresql S80sendmail -> ../init.d/sendmail S85gpm -> ../init.d/gpm S87iiim -> ../init.d/iiim S90canna -> ../init.d/canna S90crond -> ../init.d/crond S90xfs -> ../init.d/xfs S95atd -> ../init.d/atd S96readahead -> ../init.d/readahead S97messagebus -> ../init.d/messagebus S97rhnsd -> ../init.d/rhnsd S99local -> ../rc.local
As illustrated in this listing, none of the scripts that actually start and stop the services are located in the
/etc/rc.d/rc5.d/directory. Rather, all of the files in
/etc/rc.d/rc5.d/are symbolic links pointing to scripts located in the
/etc/rc.d/init.d/directory. Symbolic links are used in each of the
rcdirectories so that the runlevels can be reconfigured by creating, modifying, and deleting the symbolic links without affecting the actual scripts they reference.
The name of each symbolic link begins with either a
Klinks are processes that are killed on that runlevel, while those beginning with an
initcommand first stops all of the
Ksymbolic links in the directory by issuing the
/etc/rc.d/init.d/<command> stopcommand, where <command> is the process to be killed. It then starts all of the
Ssymbolic links by issuing
After the system is finished booting, it is possible to log in as root and execute these same scripts to start and stop services. For instance, the command
/etc/rc.d/init.d/httpd stopstops the Apache HTTP Server.
Each of the symbolic links are numbered to dictate start order. The order in which the services are started or stopped can be altered by changing this number. The lower the number, the earlier it is started. Symbolic links with the same number are started alphabetically.
One of the last things the
initprogram executes is the
/etc/rc.d/rc.localfile. This file is useful for system customization. Refer to Section F.3, “Running Additional Programs at Boot Time” for more information about using the
initcommand has progressed through the appropriate
rcdirectory for the runlevel, Upstart forks an
/sbin/mingettyprocess for each virtual console (login prompt) allocated to the runlevel by the job definition in the
/etc/event.ddirectory. Runlevels 2 through 5 have all six virtual consoles, while runlevel 1 (single user mode) has one, and runlevels 0 and 6 have none. The
/sbin/mingettyprocess opens communication pathways to tty devices, sets their modes, prints the login prompt, accepts the user's username and password, and initiates the login process.
In runlevel 5, Upstart runs a script called
prefdmscript executes the preferred X display manager —
xdm, depending on the contents of the
Once finished, the system operates on runlevel 5 and displays a login screen.