Learn the Linux system from scratch (i)

Linux system: Time-sharing multi-user multi-tasking operating system;

Linux system Boot process:

In the Inittab configuration file:

Defines the 7 levels of the operation of the Linux system: from 0~6

0, 6: On behalf of the shutdown and restart, is not recommended to set the default operating level, otherwise the system will not work properly;

4: Not used, left to users to customize the use;

1: Single-user mode, only administrators can use;

2, 3: No graphical interface, 2 less than 3 NFS (network File system, a security hidden network sharing service)

5: With graphical interface

To view the current RunLevel: # RunLevel Pre-level current level

Toggle RunLevel: Init/telinit [0123456Ss] SS is represented as RunLevel 1

Inittab configuration file Content format:

To define a process record:

ID (2-bit identifier): Run-levels (Run level): Action (Running State): Process (script and command to run)

Action Value:

Initdefalut (default value)

Sysinit (regardless of the runlevel, as long as the system executes once)

Wait: Executes the instruction in the process, and so on after it finishes running other commands

Once: Executes the instruction in the process without ending it (not used)

Executes the command specified by the process when Ctrlaltdel:ctrl+alt+del (the default is the shutdown directive) = = = That's why the Power Bar shortcut key is the origin of the shutdown Dafa

Note: The start script location of action Sysinit is in: sysint/ect/rc.d/rc.sysinit

Then you will determine the operating level of the system, to find a different RunLevel startup script directory, by viewing the file: s start, the beginning of K to stop, the smaller the priority is higher; You can modify the file name to achieve the purpose of not allowing the system to start certain services; for example: RunLevel 3 directory/etc/rc.d/ RC3.D or/ETC/RC3.D

Ctrl + ALT + F1~F6: Start 6 terminal F7: Back to the original page

Note: If the command does not make it possible to conflict with the shortcut keys in the virtual machine, you need to change the shortcut keys for the virtual machine;

Learn the Linux system from scratch (i)