It updates and queries runlevel information for system services. Chkconfig command is used to setup, view, or change services that are configured to start automatically during the system startup. When chkconfig is run without any options, it displays usage information. In Unix-like computer operating systems, init short for initialization is the first process started during booting of the computer system.
Init is a daemon process that continues running until the system is shut down. During a boot to multiuser mode, init executes the rc script, which in turn calls other rc. In simple words it is used to list current startup information of services or any particular service, updating runlevel settings of service and adding or removing service from management. The root filesystem is the top-level directory of the filesystem.
It must contain all of the files required to boot the Linux system before other filesystems are mounted. Contains the static bootloader and kernel executable and configuration files required to boot a Linux computer. Run levels are identified by numbers. Some system administrators use run levels to define which subsystems are working, e. Whenever a LINUX system boots, firstly the init process is started which is actually responsible for running other start scripts which mainly involves initialization of you hardware, bringing up the network, starting the graphical interface.
Now, the init first finds the default runlevel of the system so that it could run the start scripts corresponding to the default run level. A runlevel can simply be thought of as the state your system enters like if a system is in a single-user mode it will have a runlevel 1 while if the system is in a multi-user mode it will have a runlevel 5.
Each runlevel designates a different system configuration and allows access to different combination of processes. The important thing to note here is that there are differences in the runlevels according to the operating system.
In addition to the standard runlevels, users can modify the preset runlevels or even create new ones according to the requirement. Runlevels 2 and 4 are used for user defined runlevels and runlevel 0 and 6 are used for halting and rebooting the system. Obviously the start scripts for each run level will be different performing different tasks. These start scripts corresponding to each run level can be found in special files present under rc sub directories.
The chkconfig tool is used in RedHat based systems like CentOS to control what services are started at which runlevels. Running the command chkconfig —list will display a list of services whether they are enabled or disabled for each runlevel.
Single User mode is a mode that a multi-user system like a Linux server can be booted into the operating system as a superuser. Booting a system into this mode does not start networking, but can be used to make changes to any configuration files on the server.
One of the most common usages for single-user mode is to change the root password for a server on which the current password is unknown. Runlevels are an important part of the core of the Linux operating system. While not something the average administrator will work with on a daily basis, understanding runlevels gives the administrator another layer of control and flexibility over the servers they manage.
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Search Search. Init scripts Init short for initialization is the program on Unix and Unix-like systems that spawns all other processes. About the Author: Matt Aurand. Common Fixes
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