F.4. SysV Init Runlevels
initlaunches or halts when initializing a runlevel. SysV init was chosen because it is easier to use and more flexible than the traditional BSD-style init process.
/etc/rc.d/directory. Within this directory, are the
rc.sysinit, and, optionally, the
rc.serialscripts as well as the following directories:
init.d/ rc0.d/ rc1.d/ rc2.d/ rc3.d/ rc4.d/ rc5.d/ rc6.d/
init.d/directory contains the scripts used by the
/sbin/initcommand when controlling services. Each of the numbered directories represent the six runlevels configured by default under Red Hat Enterprise Linux.
init. For instance, runlevel 1 (single user mode) halts any network services, while runlevel 3 starts these services. By assigning specific services to be halted or started on a given runlevel,
initcan quickly change the mode of the machine without the user manually stopping and starting services.
1— Single-user text mode
2— Not used (user-definable)
3— Full multi-user text mode
4— Not used (user-definable)
5— Full multi-user graphical mode (with an X-based login screen)
/etc/inittab. To find out the default runlevel for a system, look for the line similar to the following near the bottom of
/etc/inittab. Simple typos can cause the system to become unbootable. If this happens, either use a boot CD or DVD, enter single-user mode, or enter rescue mode to boot the computer and repair the file.