Linux basic configuration and Management 4 Linux system startup detailed

1 System-initiated process

BIOS-> mbr+boot Code-> Execute bootstrapper: GRUB-> load Kernel-> execute init-> run RunLevel

2 Start detailed

1 BIOS

The 1 BIOS refers to the basic input and output system (basic input outputs systems), typically stored in the BIOS chip on the motherboard

2 The first step in computer startup is to start the BIOS first, and then the BIOS to check the hardware and find the bootable device

3 bootable devices can be set in BIOS, including USB, CDROM, HD, etc.

2 MBR

1 MBR is 512 bytes, the first 446 bytes are boot code

The 2 BIOS "determines the device as a boot device through the last two bytes in 512 bytes of the first sector" 55AA

3 MBR just going to load the bootstrapper gurb

3 GRUB

1 Grub is now the mainstream of Linux use of the boot program

2 grub can boot almost all operating systems

3 GRUB-related files are stored in/boot/grub

4 KERNEL

The 1 MBR boot code will be responsible for locating and loading the Linux kernel

2 Linux kernel saved in/boot/vmlinuz ...

3 will also load the kernel module packaging files/boot/init ...

4 Linux to maintain the streamlining of the kernel will be some of the less commonly used drivers, functions compiled into modules, and then in the time to use dynamic loading, and these modules are saved as INITRMFS files

5 early Linux uses INITRD files, but most Linux versions now use INITRMFS to save space and be more flexible

6 command DMESG can be used to view output information of the secondary boot kernel

5 INIT

1 Init is the first process of Linux running, Init is the parent process of all processes, numbered 1

2 Invoke/etc/rc.d/rc.sysinit to initialize the system, mount the file system, and start the appropriate program according to the run level

3 Run level of Linux

0 off the machine

1 Single user mode

2 Multi-user mode with no network

3 multi-user mode on the command line

4 Not used

5 graphical interface Multi-user mode

6 reboot

4 We can view the previous and current run levels through RunLevel

5 command init can be used to view changes to the current run level

6 Single user modify root password

1 for the Kernel pass parameter "1" or "single" to enable the system into Single-user mode

2 Single user mode does not start any service

3 single user mode login directly with root, no password required

4 We can modify the root password by passwd.

5 because anyone close to our physical machine is likely to modify our root password, we can use grub encryption to prevent the password from being modified.

6 We add a row of password--md5 encrypted string in the boot setting in grub.conf

Password we can generate by Grub-md5-crypt

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