Linux basic system command

one。 Computer performance:

1. Horizontal expansion

Cluster: there are many people and great strength

a. Load balancing cluster

b. High availability cluster

c. High performance Cluster (Application layer)-Hadoop Cluster = map reduces+HDFS

two。 Scale-up application migration

{under Linux system, everything is a file}

two。 Startup of the system:

-1. Power source

-2.BIOS chip (program)

First job: power-on self-test to check whether the hardware is normal.

The second job: start the system (1. Select system startup (a. System location of the reading order problem (BIOS): hard disk network (PXE) USB disk CD/VDC...)-- 2. The system files in the hard disk need to be loaded into memory and read and run by CPU; MBR partitions: to find and guide the system to load, in other words, to help find system files (BootLoader: size 446 bytes)

LILO: embedded loading, grub: the program that guides the startup function of the system)]

-3. "We have finished loading the kernel program at this point, but we cannot run ordinary applications." load kernel

-4. At this point, we need to run the first application (init)-- [init: divide the operating system into (- chkconfig/rc.) 0-6 7 levels; each level will run the corresponding application (specify the default startup level)-- read the default level 3 (command line)]

There are several levels to remember:

0mura-shutdown level

1mura-single user mode level

3mura-command line level

5mura-graphical interface level

6mura-restart

-5.rc.local / / the system starts up and finally reads this file, and the administrator can add the command that needs to be booted here.

-6. Desktop

Learn commands to minimize interaction with the computer

Chkconfig function: specify the level at which the service starts, starts or shuts down

-h-- help View help > >-- list* example: >-- level 345 Name

* update-rc.d controls some programs to start up under Ubuntu

-f force Enforcement

[chkconfig can be used on Ubuntu and needs to be installed]

III. Basic format of Linux commands command [options] [parameters]

[]: square brackets represent optional; specify to implement a specific function of the command

The object on which the code command is executed; if it is not represented, you cannot omit the object that must be added

Long integer option (cannot be merged)

Short integer option (can be merged)

Extension (understanding): command subcommand [options] [parameters] * four. Hard links and soft links

Induction: many-to-one hard links

five。 The basic use of commonly used Linux commands

First of all, let's continue yesterday's content and expand it.

Question: what if the command is not under the path path?

1. You can run the command through the absolute path; (when the absolute path is executed = the command itself, and some naming is the system default alias (you can add it yourself)-alisa;)

Which command / / find the absolute path of the command

Or\ ls runs with a backslash

two。 Just add this path to the PATH path.

PATH=$PATH:/XXX/XXX

3.LS---// displays file information

-l / / ll view file details (attributes)

-I / / incode (attribute)

-h / / human human readable ()

-F displays the tag after the file (used to distinguish the file type)

-r display the contents of the file in reverse order

4.PWD-// displays the current directory (path)

CD----// changes to the target directory

~ represents the home directory of the current user (/ root / home)

. Represents the current directory (with. The beginning file is a hidden file)

.. One level above the current directory $OLDPWD stores the directory you passed last time

6.CD-/ / switch to the directory above the destination

7.touch---// modification timestamp

Example: > [[CC] YY] MMDDhhmm [.ss]

20 19 0 8 0 16 36. twenty-two

-a modify access time-m modify time-t specify when to modify-c modify the file Mtime, if the file does not exist, do not create the file

-SATA..atime (access time) Mtime (modify file content time) ctime (modify file properties) Mkdir / / create folder-p Recursive create multi-level subdirectory

-v shows the creation process in detail

Tree / Show all root directories

[tree: display directory and file structure in tree form]

-L 1 NUM view how many levels of subdirectories (view level one subdirectories)

-d display only catalog files

8.rm----// deletion

-f force forced deletion (folder cannot be deleted)

-I asks whether to delete the file, default command (alisa rm ='rm-i')

\ rm abc

/ bin/rm abc

-r forcibly delete directories (folders)

Expand a little bit:

1. Rm delete directory is not applicable by default-rmdir

Rmdir can only delete empty directories

two。 We will need to delete files or directories to move to the / tmp directory; / tmp directory is a temporary file directory, files that have not been accessed for 30 days will be automatically deleted. Master and group to which it belongs

Remember:

1. The storage device must have a file system installed

two。 The formatting operation is installing the file system.

The common file system format under 3.Windows: (1) .NTFS (2) .FAT32

4.echo$PATH (environment variable) variable: a named kernel

[note: variables need to be capitalized]