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077 - About runlevel

runlevel is a preset operating state on a Unix-like operating system.

A system can be booted into (i.e., started up into) any of several runlevels, each of which is represented by a single digit integer.
Each runlevel designates a different system configuration and allows access to a different combination of processes
(i.e., instances of executing programs). The are differences in the runlevels according to the operating system.
Seven runlevels are supported in the standard Linux kernel (i.e., core of the operating system).

They are:

Run Level  Description
 0 System halt; no activity, the system can be safely powered down.
 1 Single user mode; rarely used.
 2 Multiple users, without NFS (network filesystem); the same as 3, if you do not have networking.
 3

Full Multiple users, command line (i.e., all-text mode) interface; the standard runlevel
for most Linux-based server hardware.

 4 User-definable, unused.
 5 Multiple users, X11 GUI (graphical user interface); the standard runlevel for most Linux-based desktop systems.
 6 Reboot; used when restarting the system.

If the system condition is the runlevel 3, the follwoing programs(Sxxxxxx) in /etc/rc.d/rc3.d/ should be executed
(S: Start, K: Kill).

K01dnsmasq     K74nscd            S11auditd          S56xinetd
K01smartd      K75fuse            S11portreserve     S58ntpd
K01smolt       K75ntpdate         S12rsyslog         S60vsftpd
K05anacron     K76openvpn         S13irqbalance      S64mysqld
K05saslauthd   K83named           S13rpcbind         S80oracle-xe
K10psacct      K84wpa_supplicant  S14nfslock         S80sendmail
K20nfs         K87multipathd      S15mdmonitor       S85gpm
K24irda        K87restorecond     S18rpcidmapd       S85httpd
K37ndbd        K89netplugd        S19rpcgssd         S90crond
K38ndb_mgmd    K89rdisc           S22messagebus      S90kerneloops
K50netconsole  K90network         S25netfs           S95atd
K50snmpd       K95firstboot       S26haldaemon       S96avahi-daemon
K50snmptrapd   S00livesys         S26udev-post       S98cups
K69rpcsvcgssd  S00microcode_ctl   S27NetworkManager  S99livesys-late
K73winbind     S06cpuspeed        S29setroubleshoot  S99local
K73ypbind      S08ip6tables       S50bluetooth       S99webmin
K74lm_sensors  S08iptables        S55sshd

The inittab file describes which processes are started at bootup and during normal operation (e.g. /etc/init.d/boot, /etc/init.d/rc, gettys...). Init(8)
distinguishes multiple runlevels, each of which can have its own set of processes that are started. Valid runlevels are 0-6 plus A, B, and C for
ondemand entries.
An entry in the inittab file has the following format:

#id:runlevels:action:process

id:5:initdefault

If you want to change the runlevel for your server, please use the following command.

[myserver]# telinit 5

If you want to know the runlevel, please use the following command.

[myserver]# /sbin/runlevel

N 5

 



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Story | by Dr. Radut