F.2.4. /sbin/init 程序

/sbin/init 程序（也称作 init）协调余下的引导过程并为用户配置环境。

当 init 命令启动时，它成为系统里所有自动启动程序的父程序或者祖父（grandparent）程序。首先，它运行 /etc/rc.d/rc.sysinit 脚本设置环境路径、启动 swap、检查文件系统并执行所有系统初始化所需的其他步骤。例如，多数系统会使用时钟，因此 rc.sysinit 读取 /etc/sysconfig/clock 配置文件来初始化硬件时钟。另外一个示例是，如果有必须初始化的特殊串口程序，rc.sysinit 会执行 /etc/rc.serial 脚本。

然后 init 命令处理 /etc/event.d 目录中的任务，这些任务描述了在每个SysV 初始化运行级别中应该如何设置系统。运行级别（runlevel）是一个状态或者模式，它由 SysV /etc/rc.d/rc<x>.d/ 目录中列出的服务定义，其中 <x> 是运行级别号。有关 SysV init 运行级别的详情，请参考第 F.4 节 “SysV Init 运行级别”。

接下来 init 命令为系统设置源功能库，/etc/rc.d/init.d/functions，它可配置如何启动、杀死程序以及确定程序的程序号（PID）。

init 通过在正确 rc 目录中查找 /etc/inittab 中指定的运行级别启动所有后台进程。对 rc 目录编号对应其代表的运行级别。例如：/etc/rc.d/rc5.d/ 是代表运行级别 5 的目录。

当引导至运行级别 5 时，init 程序会在 /etc/rc.d/rc5.d/ 目录中查看并确定要启动和停止的进程。

下面是 /etc/rc.d/rc5.d/ 目录内容的示例：

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

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

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如这个列表所示，所有真正启动和停止服务的脚本都不在 /etc/rc.d/rc5.d/ 目录中。相反，/etc/rc.d/rc5.d/ 中的所有文件都是指向 /etc/rc.d/init.d/ 中的脚本的符号链接。在 rc 里使用符号链接以便在不影响其参考的脚本的情况下，通过重新创建、修改和删除这些符号链接重新配置运行级别。

每个符号链接的名字都以 K 或者 S 开头。以 K 开头的链接是在这个运行级别需要杀死的程序，而以 S 开头的链接是需要启动的程序。

首先，init 命令通过 /etc/rc.d/init.d/<command> stop 命令来停止目录中的所有 K 符号链接，其中 <command> 是需要杀死的程序名。然后，它他通过 /etc/rc.d/init.d/<command> start 启动所有 S 符号链接。

注意

在系统完成引导后，也可以 root 用户登录，并执行这些同样的脚本启动和停止服务。例如，/etc/rc.d/init.d/httpd stop 可用来停止 Apache HTTP 服务器。

为每个符号链接编号来指定启动顺序。可以更改这个数字可改变服务启动或停止的顺序。数字越小，就越早启动。有着相同数字的符号链接则按字母顺序启动。

注意

init 程序最后执行的是 /etc/rc.d/rc.local 文件。这个文件对于自定义系统很有用。有关使用 rc.local 文件的详情请参考第 F.3 节 “在引导时运行附加程序”。

After the init command has progressed through the appropriate rc directory for the runlevel, Upstart forks an /sbin/mingetty process for each virtual console (login prompt) allocated to the runlevel by the job definition in the /etc/event.d directory. 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/mingetty process opens communication pathways to tty devices^[18], 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 /etc/X11/prefdm. The prefdm script executes the preferred X display manager^[19] — gdm, kdm, or xdm, depending on the contents of the /etc/sysconfig/desktop file.

完成后，系统将在运行级别 5 中运行并显示登录屏幕。

^[18] Refer to the Red Hat Enterprise Linux Deployment Guide for more information about tty devices.

^[19] Refer to the Red Hat Enterprise Linux Deployment Guide for more information about display managers.

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F.2.4. /sbin/init 程序

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