Linux Basics Summary

Features of Linux

-Free/Open source
-Multi-threaded/multi-user support
-Good safety
-Superior in memory and file management

shutdown Command
Shutdown-h now (shut down immediately) Shutdown-r now (restart the computer) reboot (restart the computer)

go to Desktop

StartX

User Login

log in as little as possible with the root account login, because it is the system administrator, the maximum permissions, unavoidable operation error. You can log in with a normal user, log in, and then use the "Su-" command to switch to system administrator status.

User Logoff

Enter logout at the prompt

Linux file system is a hierarchical tree directory structure , the top of this structure is the root directory "/", and then create another directory in this directory, a deep understanding of the Linux file directory is very important

- /
-Root, which holds the files of the root user
-Home, storing relevant files for ordinary users
-Bin, a directory of commonly used commands, such as Vi,su
-Sbin, you must have permission to use the command
-MNT, default mount directory for CD-ROM and floppy drive
-etc, storing the relevant files of the configuration
-Var, which stores frequently changing files, such as sock files for network connections
-Boot, store the boot system boot file
-usr, install the default directory for a software equivalent to the program files under Windows

Here are some of the more commonly used commands and how to use them:

pwd, showing which path is currently under

User Management for Linux

useradd user name, adding user

"Case" Useradd xiaoming

passwd user name, password for new user

"Case" passwd xiaoming, modify Xiaoming's password

Userdel user name, delete user

"Case" Userdel xiaoming, deleting the user but saving the user home directory
"Case" userdel‐xiaoming, deleting users and user home directories

logout, current user launch

Who am I, current user who

CD, change directory

ls, listing files and directories

Ls‐a, displays all files in the directory, including hidden files

ls‐l, display long list format

mkdir, creating a directory

rmdir, delete empty directory

Touchto create an empty file

cp, copy command

"Case" Cp‐r dir1 dir2, recursive copy command (copy subdirectory information)

mv, moving files and changing file names

rm, deleting files and directories

RM‐RF *, delete all content, including directories and files, R for recursion, F to force

Ln, creating a symbolic connection, similar to creating a shortcut to a file

ln‐s Source target

"Case" Ln‐s/etc/inittab inittab,inittab pointing to the actual file/etc/inittab Inittab

More, show file contents with paging, CTRL + PAGE UP, Sky grid down

Less, display file contents with pagination

grep, querying for content in text

"Case" assumes that there is a file test.cpp with the Hello keyword, you can use the grep name command to find, grep n "Hello" test.cpp,n indicates that the nth row appears

|, Pipeline command, on Linux and UNIX systems, give the result of the previous command to | command processing

"Case" ls‐l/etc/| More

Man [command], Helper, similar to help in DOS

Find, search for files and directories. In Linux, because file systems are composed of hierarchical structures, it is not easy to find specific files and directories throughout the system. and the "Find" command solves the above problem

search for and display files and directories of the specified name in a specific directory

"Case" Find/-name man: Meaning to start searching for a file or directory named man from the root directory

Search for files or directories that have been accessed/changed over time

"Case" find/home-amin-10: Files or directories accessed within 10 minutes
"Case" find/home-atime-10: Files or directories accessed within 10 hours
"Case" FIND/HOME-CMIN-10: Changed files or directories within 10 minutes
"Case" Find/home-ctime + 10: Changed files or directories 10 hours ago

Search for files of a specified size

"Case" find/home-size +10k: Meaning to find files of size 10k in the/home directory

REDIRECT command

ls-l > A.txt, the contents of the list are written to the file A.txt (overwrite write)

Ls-al >> Aa.txt, the contents of the list are appended to the end of the file Aa.txt

Enter information from the file: Database_program < Database_data

En, view environment variables

Compression and decompression

Processing. zip files in zip and unzip

Basic use of the zip command

Zip File.zip *:zip After the compressed file name, enter the file to be compressed after it

Automatically delete the original file after compression

"Case" Zip m file.zip to.txt: to.txt files are compressed into file.zip files, To.txt will be automatically deleted

To compress subdirectories together

"Case" zip‐r file.zip *: Compress subdirectories in the current directory together

Ignore contents of subdirectories

"Case" zip‐j file.zip *

Remove compressed or unnecessary compressed files

"Case" zip‐n. mpg:. jpg:. gif: The middle of the first file is separated by ":"

Compress files after a day

"Case" Zip‐t 080915 file.zip: File compression after August 9, 2015 in the current directory

Do not compress the original file of the linked file

"Case" Zip‐y file.zip *

Compression ratio problem, -1~-9, where-9 of the compression rate is highest

"Case" zip-9 file.zip *

Exclude files that do not need to be compressed

"Case" Zip File.zip * x file2.txt: Excludes file2.txt files in the current directory when compressing

Unzip the. zip file with the unzip command

Unzip files directly

"Case" unzip File.zip

Exclude files that do not need to be decompressed

"Case" unzip file.zip‐x file2: Except for the File2 file, all other files are uncompressed

View the contents of a compressed package

Case Unzip‐z File.zip: View the contents of the File.zip compressed package, or use "-l" "-V" to view the contents of the compressed package

Process. gz files with gzip and gunzip

Each user in Linux must belong to a group and cannot be independent of the group. In Linux, each file has the concept of owner, group, and other groups .

1) Owner: Generally the creator of the file, who created the file, becomes the owner of the file naturally. You can see the owner of the file with the Ls‐ahl command. You can also use the Chown user name file name to modify the owner of the file.

2) file group: When a user creates a file, the group in which the file is located is the group that the user is in, the Ls‐ahl command lets you see all the groups of the file, or you can use the CHGRP group name file name to modify the group in which the file resides.

3) Other groups: except for the owner of the file and the user in the group, other users of the system are other groups of files.

file Permissions

the contents shown in Ls-l are as follows:

-rwxrw-r‐-1 root root 1213 9 09:39 ABC

10 characters to determine what different users can do with a file

The first character represents a file (-), a table of contents (d), and a link (l)

The remaining characters are set per 3 (RWX), read (R), write (W), execute (x)

First set of rwx: The permissions of the file owner are read, write, and execute

Second set of rw-: Permissions for users of the same group as the file owner are read, write, but cannot be executed

Third group r--: permissions for other users who are not in the same group as the file owner are read and cannot be written and executed

Also available as a number: R=4,w=2,x=1 so rwx=4+2+1=7

1 indicates the number of files connected

Root indicates that the user

The second root indicates the group to which the user resides

1213 indicates file size (bytes)

9 09:39 indicates last modified date

ABC indicates file name

commands to change permissions

chmod Changing the permissions of a file or directory

chmod 755 ABC: Give ABC permission rwxr-xr-x

chmod U=RWX,G=RX,O=RX ABC: ibid. u= User Rights, g= group permissions, o= different groups of other user rights

chmod u-x,g+w ABC: for ABC to remove user-executed permissions, increase group Write permissions

chmod a+r ABC: Add read permissions to all users

Change owner (chown) and user Group (CHGRP) commands

Chown xiaoming ABC: Change the owner of ABC to Xiaoming

CHGRP Root ABC: Change the group that the ABC belongs to IS root

Chown root./ABC: Change ABC the owner of this directory is root

Chown‐r root./ABC: Change the ABC directory and the owner of all files and directories below it is root

Change the user group

When you add a user, you can specify which group to add the user to, as well as root administrative permissions to change the group in which a user resides

USERMOD‐G Group name User name

You can change the initial directory of the user login by using the USERMOD‐D directory name User name.

Linux Partitioning

The partition of the hard disk is mainly divided into basic partition (Primary portion) and extended partition (Extension portion) two kinds. Just for a hard disk, the sum of the basic and extended partitions cannot be more than 4, and the basic partition can be used immediately but cannot be partitioned. The extended partition must be partitioned before it can be used, meaning it must also be partitioned two times. So what's the extension partition going on? It is a logical partition (Logical portion), and there is no limit to the number of logical partitions

For Windows users, several partitions have several drives, and each partition obtains a letter identifier, which can then be used to specify the files and directories on this partition. Their file structures are independent and very well understood. But it's a bit annoying for these users to get started with Linux at first. Because for Linux users, regardless of a few partitions, to which directory to use, it boils down to only one root directory, a separate and unique file structure . Each partition in Linux is used to form part of the entire file system. Because it uses a processing method called "load" , its entire file system contains a set of files and directories, and a partition and a directory link together. The partition to be loaded will make its storage space available in this directory.

Here are a few important commands

mount Command

Mount [-parameters] [device name] [Mount Point]

Uninstall Command

Umount [Mount Point]

View disk usage

DF [-parameters]

Df-h

Df‐l

DF [Directory full path] to see which partition a directory is in

View Linux system partition specifics

Fdisk‐l

Shell Programming

The fact that the command language interactively interprets and executes user input commands is only one aspect of shell functionality. The shell can also be used for programming. It provides a means of defining variables and parameters, as well as a rich program control structure. Using shell programming is similar to a DOS batch file, called a shell script, also called a shell program or shell command file.

Shell script file:

is a text file

Collection of commands

have permission to execute

Execution mode (./file name)

With export you can temporarily add a system path, such as export path= $PATH home/bin:/root/test/t1, Output environment path, reference the original value $path, $HOME represents the working home directory, is the path delimiter

Shell wildcard characters

* represents multiple letters or numbers

? Represents a letter or a number

"Case" ls A * ls a? LS f080[1-6].tif

escape character \

"Case" ls/mnt/win1/my\documents

single quotation marks: Do not process any variables and commands

"Case" Echo ' Welcome $NAME, the date is date '

double quotes: Handling variables but not processing commands

"Case" echo "Welcome $NAME, the date is date"

Reverse quotation marks: Each word in the quotation mark as a command, if the variable is evaluated first and then treated as a command

"Case" echo "Welcome $NAME, the date is ' date '"

Check History

History, viewing the historical record of used commands

History 5, this note shows the 5 most recently used commands

!5, this description executes a command with a history number of 5

!ls, this note executes the last command that starts with "LS"

Linux Basics Summary