The Linux services are organized by runlevels. There are seven runlevels and each runlevel executes a specified set of scripts. All scripts are collectively stored in /etc/rc.d/init.d directory and all runlevels also have their own directory which contains some start and stop scripts. The scripts associated with each runlevel can be found in /etc/rc.d directory:
rc0.d
rc1.d
rc2.d
rc3.d
rc4.d
rc5.d
rc6.d
Runlevel and description of each runlevel is given below:
Runlevel Description
init 0 Halt (Do not set initdefault to this)
init 1 Single-user mode, for maintenance, repairs,backups and restores.
init 2 Multiuser with some networking services ( for system performance)
init 3 Multiuser with networking
init 4 Unused (customized to use)
init 5 X11 console, Defaults to a GUI desktop with networking
init 6 Reboot (Do not set initdefault to this)
To list all runlevels
cat /etc/inittab
To switch particular runlevel
init x (eg. init 6 - to reboot)
To list all service settings run the following command:
/sbin/chkconfig --list
To list the entry for the sshd daemon, execute the following command:
/sbin/chkconfig --list | grep sshd
To know which services get started for runlevel 3:
/sbin/chkconfig --list | grep '3:on'
The httpd service to start up at runlevel 5 we would issue the following command:
/sbin/chkconfig --level 5 httpd on
To see graphical tool that allows you to view which services will start for each runlevel
system-config-services
Otherwise go to System - Administration - Services
The graphical tool also allows you to start, stop, restart, enable, disable each services and to customize the services for particular runlevels.
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rc0.d
rc1.d
rc2.d
rc3.d
rc4.d
rc5.d
rc6.d
Runlevel and description of each runlevel is given below:
Runlevel Description
init 0 Halt (Do not set initdefault to this)
init 1 Single-user mode, for maintenance, repairs,backups and restores.
init 2 Multiuser with some networking services ( for system performance)
init 3 Multiuser with networking
init 4 Unused (customized to use)
init 5 X11 console, Defaults to a GUI desktop with networking
init 6 Reboot (Do not set initdefault to this)
To list all runlevels
cat /etc/inittab
To switch particular runlevel
init x (eg. init 6 - to reboot)
To list all service settings run the following command:
/sbin/chkconfig --list
To list the entry for the sshd daemon, execute the following command:
/sbin/chkconfig --list | grep sshd
To know which services get started for runlevel 3:
/sbin/chkconfig --list | grep '3:on'
The httpd service to start up at runlevel 5 we would issue the following command:
/sbin/chkconfig --level 5 httpd on
To see graphical tool that allows you to view which services will start for each runlevel
system-config-services
Otherwise go to System - Administration - Services
The graphical tool also allows you to start, stop, restart, enable, disable each services and to customize the services for particular runlevels.
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