Linux Fundamentals 01

(1) LS
-L: Long format
File type: the
-: Normal file (f)
D: Catalog file
B: Block device files (blocks)
C: Character device file (character)
L: Symbolic Link files (symbolic link file)
P: Command pipe file (pipe)
S: Socket file (socket)
Example: Ls-ld/root displays information about the/root itself.

(2) file permissions: 9-bit, every 3-bit group, each group: rwx (Read, write, execute), r--
Number of hard links to files
Owner of the file
Genus Group of files
File size (size), in bytes
Timestamp (timestamp): Last Modified Time
Access: Access
Modified: Modify, the file content has changed
Change: change,metadata, meta data
-H: Do the unit conversion (the file size is displayed in human readable form)
-A: Show hidden files starting with.
. Represents the current directory
.. Represents the parent directory
-A: And-a differ only. And.. Different.
-D: Display the directory's own properties
-i:index node, inode (displays the index number of the file)
-R: Reverse Display
-R: Recursive (Recursive) display

(3) Cd:change directory
Home directory, home directory, home directory (enter CD separately, enter home catalog)
CD ~username: Enter the home directory of the specified user
CD-: Switch back and forth between the current directory and the previous directory

(4) Displays the commands in the current cache (that is, commands that have been entered)
Hash

(5) Type: Shows which type the command belongs to (internal command or external command)

(6) To obtain the use of the command help:
Internal command:
Help COMMAND
External command:
COMMAND--help

(7) Command manual: Manual
Mans COMMAND
Example: Man ls
Mans Mount
Man 2 read//Displays the second chapter of the Read command.
Export lang=en//After import, the English command manual is displayed.

Find where the command appears in the manual: Whatis command

Sub-chapters:
1: User command (/bin,/usr/bin,/usr/local/bin)
2: System call
3: Library User
4: Special files (device files)
5: File Format (configuration file syntax)
6: Game
7: Miscellaneous (Miscellaneous)
8: Management Command (/sbin,/usr/sbin,/usr/local/sbin)

(8) Command format description
<>: Required
[]: Optional
... : multiple times can occur
|: Choose one More
{}: Grouping

(9) Man:
Name: command names and features brief description
Synopsis: Usage notes, including available options
DESCRIPTION: A detailed description of the command function, which may include the meaning of each option
Options: Explaining the meaning of each option
Files: The configuration file associated with this command
BUGS:
EXAMPLES: Using the example
See ALSO: Another reference

Flip Screen:
Turn back one screen: SPACE
Turn One screen forward: b
Turn back one line: ENTER
Turn One line forward: K

Find:
/keyword: Backwards
N: Next
N: Previous

? KEYWORD: Forward
N: Next
N: Previous
Q: Exit

(Ten) Hwclock
-W: Sets the hardware clock from the system time.
-S: Sets the system clock from the hardware clock.

(11) Display system environment variables
Printenv

(12)
/root/-the root user (Superuser) home directory.
/boot: System boot related files, such as kernel, INITRD, and Grub (bootloader)
/initrd/-is used to mount the directory of the initrd.img image file when the computer starts up and the directory to load the required device modules.

/dev: Device files
Device files:
Block devices: Random access, data blocks
Character Devices: Linear access, by character
Device number: Main device number (major) and secondary device number (minor)
/etc: Configuration file
Home directory for users, the home directory of each user is usually the default of/home/username
/root: Administrator's home directory;
/lib: library file, is kernel-level. Only shared libraries that are used by programs in the/USR directory do not have to be placed in the/lib directory. Only the libraries required for the programs under/bin and/sbin need to be placed in the/lib directory.
static libraries,. A: Each program is loaded.
Dynamic libraries,. dll,. So (Shared object): Loaded only once to memory, other programs do not need to be loaded repeatedly, can be used directly.
/lib/modules: Kernel module files

Additional Instructions:
/lib/-contains many library files that are used by programs in/bin/and/sbin/. The directory/usr/lib/contains more library files for user programs.
The/lib directory is placed under the/bin and/sbin directories required by the program's library files. The name of the file under the/lib directory follows the following format:
Libc.so.*
ld*

/media: mount point directory, usually mounted on mobile devices, CDs, etc.
/MNT: mount point directory, additional temporary file system
/OPT: Optional directory, the installation directory for third-party programs. But at present this change, the third party program all put under Usr/local.
/proc: Pseudo file system, kernel mapping file (the temporary mapping file generated after the system is running).
/sys: Pseudo file system, a property mapping file associated with a hardware device.
/tmp: Temp file (/TMP gives all system users read and write rights. ),/var/tmp
/var: a variable file
/bin: Executable files, user commands in this folder.
/sbin: Manage commands in this folder. The storage location of many system commands (for example, shutdown).

/usr: (Full name: Universal GKFX, Read-only) global shared read-only file.
/usr/bin
Many system commands are also included in the/usr/sbin directory/usr/sbin.
/usr/lib at the system level.

/usr/local: Third-party software installation directory.
/usr/local/bin
/usr/local/sbin
/usr/local/lib user-level.

(13), naming rules:
1, the length can not exceed 255 characters;
2. Cannot use/when file name
3. Strictly case-sensitive

(14)
mkdir: Creating an empty Directory
-P: Simultaneous creation of multi-level catalogs
-v:verbose More information
Example: Mkdir-p/root/x/y/z
Mkdir-pv/root/x/y/z

To create:/mnt/test/x/m and/mnt/test/y two directories, the command is as follows:
mkdir-pv/mnt/test/x/m/mnt/test/y
Mkdir-pv/mnt/test/{x/m,y}

(15) Command line expansion
To create the following 4 directories under/mnt/test2/:
A_b, A_c, D_b, D_c
For example:
Observe the following rules:
(a+d) (b+c) =AB+AC+DB+DC
{a,d}_{b,c}=a_b,a_c, d_b, D_c
Here's how:
mkdir-pv/mnt/test2/{A,d}_{b,c}

# Tree: View directory tree

Delete directory: rmdir (remove directory)
Delete Empty Directory
-P: Delete to the previous level non-empty directory.

(16) file creation and deletion
# Touch main function is not to create files, mainly to modify the file timestamp.
-A: Change the access time only. Example: Touch-a a file
-M: Change the modification time only.
-T: Make access/modification time. Example: Touch-m-T 201807011211 a file
-C
Access: Accessing Time
Modify: Modification Time
Change: Changes time, this time is not modifiable.

(17), delete file
RM is an alias for Rm-i. To use native RM, you can use \RM.
-I: Interactive commands
-F: Force delete.
-R: Recursive delete

For example: RM-RF/: Delete the root directory, and all files under the root directory.

Linux Fundamentals 01