First, the structure of this chapter
Boot process
Start fault exclusion
Service Control and switching the operating level
Optimization of the startup process
Second, the boot process:
1, the boot code in the first sector of a disk. *** The first sector is damaged, the system will not boot.
2, the boot process overview
3, init process
By the linux kernel load and run / sbin / init program
The system is the first process
PID (process mark) is always No. 1
Third, the exclusion of start fault:
1, repair MBR sector failure
a, cause of the malfunction:
Viruses, and other damage caused by ***
Incorrect partitioning, disk read and write misuse
b, Symptom:
To find a boot program, start interrupt
Unable to load the operating system, turned black
c, Solutions:
You should make a backup of work ahead
In CD-ROM boot into emergency mode
Restore from a backup file
The first step: mbr boot sector on the first disk backup to other non-local disks. Now first of all other disks to create a new folder mkdir / data for backup mbr boot sector.
Input dd if = / dev / sda of = / data / sda.mbr.bak bs = 512 count = 1
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2, repair the GRUB boot failure:
a, cause of the malfunction:
GRUB boot loader in the MBR is destroyed
grub.conf file is missing, the boot configuration error
b, Symptom:
System boot stagnation, display "grub>" prompt
c, Solutions
Try to manually enter the boot command
Enter emergency mode, rewritten or restored from a backup grub.conf
Grub program to rebuild MBR sector
3, forget the root password
a, cause of the malfunction:
Forget the root password
b, Symptom:
You can not require root privileges management operations
If there is no other available accounts, will not login
c, Solutions
Enter emergency mode, reset your password
Fourth, the system services control and switching the operating level
1, system services control:
Common ways:
systemctl control type service name
Control Type
start: Start
stop: Stops
restart: Restart
reload: reload
status: check the service status
2, run level of the system
a, run-level view:
:( runlevel command can only view switching operation level of the current run level)
systemctl tool :( can view the default run level)
b, temporary switch to run level
init command: (init command parameter is the corresponding run level number)
systemctl tools: (systemctl command parameter is the specific target)
Systemd unit type
| Unit Type | extension name | Explanation |
| service | .service | Describe a system service |
| socket | .socket | A description of inter-process communication socket |
| device | .device | Describes a core recognition device file |
| mount | .mount | Describe a file system mount point |
| Automount | .automount |
Description Automatic a mount point of the file system |
| Swap | .swap | Describes a switching device memory or swap file |
| psth | .path | Describe a file system file or directory |
| timer | .timer | Describes a timer (for the scheduled tasks to achieve similar cron) |
| snapshot | .snapshot | To save the state of a systemd |
| scope | .scope |
Use systemd external bus interface creation process programmatically |
| Slice | .slice | Describes a set of management processes through the living Cgroup levels of the organization |
| Target | .target | Describe a group of cells systemd |
So run level corresponding to the target Systemd
| Run Level | systemd的target | Explanation |
| 0 | target | Off, when using this level will host closed |
| 1 | rescue.target | Single-user mode, no password is required to log verification system, used for system maintenance |
| 2 | multi-user.target | User-defined / run-level domain-specific default equal to 3 |
| 3 | multi-user.target | Full multi-user mode interface characters, most of the server host is running at this level |
| 4 |
multi-user.taget | User-defined / run-level domain-specific default equal to 3 |
| 5 | graphical.target | Multi-user mode graphical interface provides a graphical desktop environment |
| 6 | reboot.target | Reboot, reboot the host will use this level |
Fifth, to start the optimization process
1, system service management tools
a, ntsysv tool (pseudo terminal, boot from the start)
Intercommunication a visualization window
You can run on an ASCII terminal.
Facilitating the centralized management of multiple services
b, systemctl tools (better)
Intercommunication not provided, visualization window
Single service management more efficient
2, start and control system services
a, ntsysv system service management tools
ntsysv
ntsysv --level level list
b, see the system start-up and control services
View the status of system services start
systemctl is-enabled service name
Start setting the system state services
systemctl enable / disable service name
enable: next boot from the start disable: next time you turn not from Kai