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What is run level what is the use ?

Posted on 2008-06-18
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What is runlevel what is it use ?

i have list of process .. that shows different run levels .. what does it mean?

is this specific to unix ?

[root@radarcltransprt ~]# chkconfig --list
NetworkManager  0:off   1:off   2:off   3:off   4:off   5:off   6:off
NetworkManagerDispatcher        0:off   1:off   2:off   3:off   4:off   5:off   6:off
acpid           0:off   1:off   2:off   3:on    4:on    5:on    6:off
anacron         0:off   1:off   2:on    3:on    4:on    5:on    6:off
apmd            0:off   1:off   2:on    3:on    4:on    5:on    6:off
atd             0:off   1:off   2:off   3:on    4:on    5:on    6:off
auditd          0:off   1:off   2:on    3:on    4:on    5:on    6:off
autofs          0:off   1:off   2:off   3:on    4:on    5:on    6:off
avahi-daemon    0:off   1:off   2:off   3:on    4:on    5:on    6:off
avahi-dnsconfd  0:off   1:off   2:off   3:off   4:off   5:off   6:off
bluetooth       0:off   1:off   2:on    3:on    4:on    5:on    6:off
conman          0:off   1:off   2:off   3:off   4:off   5:off   6:off
cpuspeed        0:off   1:on    2:on    3:on    4:on    5:on    6:off
crond           0:off   1:off   2:on    3:on    4:on    5:on    6:off
cups            0:off   1:off   2:on    3:on    4:on    5:on    6:off
dc_client       0:off   1:off   2:off   3:off   4:off   5:off   6:off
dc_server       0:off   1:off   2:off   3:off   4:off   5:off   6:off
dhcdbd          0:off   1:off   2:off   3:off   4:off   5:off   6:off
dovecot         0:off   1:off   2:off   3:off   4:off   5:off   6:off
dund            0:off   1:off   2:off   3:off   4:off   5:off   6:off
firstboot       0:off   1:off   2:off   3:on    4:off   5:on    6:off
gpm             0:off   1:off   2:on    3:on    4:on    5:on    6:off
haldaemon       0:off   1:off   2:off   3:on    4:on    5:on    6:off
hidd            0:off   1:off   2:on    3:on    4:on    5:on    6:off
httpd           0:off   1:off   2:off   3:off   4:off   5:off   6:off
ibmasm          0:off   1:off   2:off   3:off   4:off   5:off   6:off
ip6tables       0:off   1:off   2:on    3:on    4:on    5:on    6:off
ipmi            0:off   1:off   2:off   3:off   4:off   5:off   6:off
iptables        0:off   1:off   2:on    3:on    4:on    5:on    6:off
irda            0:off   1:off   2:off   3:off   4:off   5:off   6:off
irqbalance      0:off   1:off   2:on    3:on    4:on    5:on    6:off
kdump           0:off   1:off   2:off   3:off   4:off   5:off   6:off
kudzu           0:off   1:off   2:off   3:on    4:on    5:on    6:off
lisa            0:off   1:off   2:off   3:off   4:off   5:off   6:off
lm_sensors      0:off   1:off   2:on    3:on    4:on    5:on    6:off
lvm2-monitor    0:off   1:on    2:on    3:on    4:on    5:on    6:off
mcstrans        0:off   1:off   2:on    3:on    4:on    5:on    6:off
mdmonitor       0:off   1:off   2:on    3:on    4:on    5:on    6:off
mdmpd           0:off   1:off   2:off   3:off   4:off   5:off   6:off

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Question by:jaisonshereen
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omarfarid earned 200 total points
ID: 21815507
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by:torimar
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ID: 21815596
Yes, runlevels are specific to Unix and Linux systems and refer to states of the system in terms of processes and services started. Usually, a linux system is fully functional at runlevel 5, whereas at runlevel 6 it is rebooted and on runlevel 0 it shuts down.

In a very wide and inaccurate way, some of the lower runlevel could be compared to the Safe Mode options in Windows.

Read more here:
http://www.unixtools.com/linux-runlevels.html
http://en.wikipedia.org/wiki/Runlevel
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by:Pétur Ingi Egilsson
Pétur Ingi Egilsson earned 100 total points
ID: 21815789
Usually servers run on Runlevel 2 without a graphical interface ( text only )
runlevel 5 is often the default runlevel on Workstation/Desktop computers.

you can find out your current runlevel by typing `runlevel` at the console.
You can switch between runlevels by example: `init X` or `telinit X` replace X with 1-5.

switching to runlevel 0 will halt Linux.
swithcing to runlevel 6 will restart Linux.
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by:eager
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ID: 21823558
The listing says which system services should be run in the different run levels.  Run levels are system operation states.  Higher run levels have increasing functionality:  Run level 1 is single user mode.  On your system, the list says that at run level 1, cpuseed and lvm2-monitor are run, but nothing else.  

When you change from one runlevel to another, services will be started or stopped based on this list. Run level 2 is multiuser, without NFS  Run level 3 adds NFS.  Runlevel 5 adds graphics.  

You can see that on your system, some services are never run, like dhcpd.  Some are run in any multi-user mode, like crond or cups.  Others are run only for particular levels, say, vncserver on runlevel 5, which require graphics.  
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by:omarfarid
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"Higher run levels have increasing functionality" Does this mean that run level 6 is the highest run level !! it is a reboot level.
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by:gheist
ID: 21825266
Runlevels are SystemV specific thing they are in Solaris, HP-UX , but not in Tru64 or any BSD.
chkconfig is Linux specific.
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by:eager
ID: 21834730
omarfarid:  From level 1 to 5, higher levels have greater functionality.  Level 6, as you note, causes a reboot of the system.  
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