1, Basic format of command

command prompt

[root@localhost~]#

Of which:

Command format

command [option] [parameter]

==Note: = = individual commands do not follow this format. When there are multiple options, they can be written together to simplify options and complete options

-a equals – all

file type

-rw-r--r--. 1 root root 1648 5 October 18:11 initial-setup-ks.cfg
	-File type(- file d catalogue l (soft link file)
	rw-        r--         r--
	u owner     g Group      o someone else
	r read  w write   x implement  linux Each of the three permissions is a group
1 Represents the first reference count root Second for owner root For the group to which it belongs, 1648 is the size, followed by the last modification time and file name

There is no suffix or software type in Linux. There is only one system type

The file type is identified by the first bit of permission bit, and every three bits are a group

Query contents in directory: ls

ls [option] [File or directory]
Options:
	-a		Show all files, including hidden files
	-l		Show details
	-d		View directory properties
	-h		Humanized display file size
	-i		display inode        

Each file has its own id, which can be viewed through - i

You can view file permissions through - d

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2, File processing command

Directory processing command and file processing command

Create directory: mkdir

mkdir -p [Directory name]
	
	-p		Recursive creation     Create a list of directories
	Original English meaning of the order: make directories

Switch Directory: cd

cd [catalogue]
Original English meaning of the order: change directory

Simplify operation
cd ~		Home directory of the current user in the machine
cd
cd -		Enter last directory
cd ..		Enter the upper level directory
cd .		Enter current directory

• **Relative path: * * Find by referencing the current directory

For example:[root@imooc~]# cd ../usr/locaa/src/

• **Absolute path: * * specify from the root directory, and search recursively one level at a time. In any directory, you can enter the specified location

For example:[root@imooc~]# cd /etc/

You can press tab twice to complete automatically, identify directory completion, or command completion

Delete empty directory: rmdir

rmdir[Directory name]
Original English meaning of the order: remove rmpty directories
 Only empty files can be deleted

Delete file or directory: rm

rm -rf [File or directory]
	Original English meaning of the order: remove
 Options:
	-r 		Delete directory
	-f		force
 Never execute rm -rf /    It will crash the system and delete it directly Linux New operating system

Copy command: cp

cp [option] [Source file or directory] [Target directory]
	Original English meaning of the order: copy
 Options:
	-r		duplicate catalog
	-p		Copy file attributes
	-d		If the source file is a linked file, copy the linked attributes
	-a 		amount to -pdr
	
ll amount to ls -l

Cut or rename command: mv

mv [Source file or directory] [Target directory]
Original English meaning of the order: move

If there is no target directory, the default is to modify the source file name. If there is, it is the rename command

Common directory functions

/root directory
/bin Command save directory (commands that can be read by ordinary users)
/boot Startup directory, startup related files
/dev Device file saving directory
/etc Profile save directory
/home Home directory of ordinary users
/lib System library save directory
/mnt System mount directory
/media Mount directory
/root Super user's home directory
/tmp Temporary directory
/sbin Command save directory (a directory that can only be used by super users)
/proc Direct write to memory
/sys
/usr System software resource directory
/var System related documents

bin

Bin and sbin under the root directory and bin and sbin under usr are used to save system commands. Under the bin directory, any user can execute, while the commands under sbin can only be executed by super users

dev special file

etc configuration file

Home home directory of ordinary users

root super user home directory

lib function library, function library

misc media mnt mount directory

The proc and sys directories cannot be operated directly. These two directories store the overload point of memory. They are written directly to memory and cannot be operated

Files can be placed in the home directory root or home, and in the tmp directory. Others are not recommended

Link command: ln

ln -s [Original document] [Target file]
Original English meaning of the order: link
 Function Description: generate linked file
	Options:    -s   Create soft link

• Hard link features:

1. Having the same i node and storage block can be regarded as the same file
2. Can be identified by i node
3. Cannot cross partition
4. Cannot be used against a directory

If the user needs to check a file, first go to a file index table to find the corresponding file, and then take it out and return it to the user

Only files can create hard links

A hard link is equivalent to two different access points to a file

• Soft connection features:

1. Similar to Windows shortcuts
2. Soft link has its own I node and Block, but only the file name and I node number of the original file are saved in the data Block, and there is no actual file data
3. lrwxrwxrwx l soft connection soft connection file permissions are lrwxrwxrwx
4. Modify any file and change the other
5. Delete source file, soft link cannot be used

Soft link is equivalent to a shortcut. When searching through soft link, users first find the id of the soft link in the file index, find a file that stores all the IDs of the corresponding file through the id, and then find it in the index through the file

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Soft links must be written from the root directory

3, File search command

File search command locate

locate file name
 Searching by file name in the background database is faster

/var/lib/mlocate
#The background database searched by the locate command

updatedb
 Update database

The locate command will only search in the background database, so it is fast, but the database is not updated in real time. Its update cycle is one day. We can also use the updatedb command to force the update.

Disadvantages:

You can only search by file name

/etc/updatedb.conf configuration file

• PRUNE_BIND_MOUNTS = "yes"

#Turn on search restrictions

• PRUNEFS =

#File types not searched when searching

• PRUNEPATHS =

#When searching, do not search the path of

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Just like the login filter, it does not search the specified path

Command search commands whereis and which

whereis Command name
#Search the path of the command and the location of the help document
 Options:
	-b: 		Find executable
	-m: 		Find help files for
which file name
#Search the path and alias of the command

Not all commands can be found. For example, cd command can only find help documents. Some commands are Linux shell commands, which are necessary for user interaction and are built-in Linux.

PATH environment variable

PATH Environment variable: defines the path of the system search command
[root@localhost~]#echo $PATH
/usr/lib/qt-3.3/bin:
/usr/local/sbin:/usr/local/bin:/sbin:/bin/usr/sbin:/usr/bin:/root/bin

File search command find

find [Search scope] [search criteria]
#search for file

find / -name install.log
#Avoid large-scale search, which will consume system resources
#find is to search the system for qualified file names. If you need to match, use wildcard matching, which is an exact match

Fuzzy query find by name

Wildcard fuzzy query in Linux

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find/root -iname install.log
#Case insensitive
find /root -user root
#Search by owner
find /root -nouser
#Find files without owners

Linux is strictly case sensitive

Files without owners are generally garbage files

1. The files in proc and sys are generated by the kernel. It is likely that the files without owner belong to normal files
2. If you use u disk to transfer files from windows to Linux, there may be no owner

Find by time

find /var/log/ -mtime +10
#Find files modified 10 days ago

-10		10 Documents modified within days
10		10 Documents modified on the same day
+10		10 Files modified days ago

atime		File access time
ctime		change attributes of files
mtime		Modify file content

Find by file size

find . -size 25k
#Find files with a file size of 25KB
#there. That is, the current directory k is lowercase

-25k		Less than 25 KB Documents
25k			Equal to 25 KB Documents
+25k		Greater than 25 KB Documents

find . -inum 262422
#Find the file whose i node is 262422

Complex find query

find /etc -size +20k -a -size -50k
#Look for files larger than 20KB and smaller than 50KB in the / etc / directory
-a		and		Logic and, both conditions are met
-o		or		Logical or, one of the two conditions can be satisfied

find/etc -size +20k -a -size -50k -exec ls -lh {} \;
#Find files larger than 20KB and smaller than 50KB in the / etc / directory and display details
#-exec/-ok command {} \; Perform actions on search results

Generally, it is troublesome to execute after the query, so - exec ls -lh {} is added; For such a command, this is a standard format. As long as - exec is written, the following {} must be written; Execute the second statement in the middle

String search command grep

grep [option] String file name
#Match matching strings in the file
 Options:
	-i		ignore case
	-v		Exclude specified string (reverse)

Search for the corresponding string from the file

All items will be listed as long as they are included

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The difference between find command and grep command

• find command: search for qualified file names in the system. If you need to match, use wildcard matching. Wildcard matching is perfect.
• grep command: search for qualified strings in files. If matching is needed, use regular expression to match. Regular expression contains matching

Use find to search for files or file names, and grep to search for content

4, Help command

Help command man

man command
#Get help for the specified command

man ls
#View help for ls

man's level

See what level of help the command has

man -f   	command
 amount to
whatis		command

give an example:
man -5 passwd
man -4 null
man -8 ifconfig

View all help related to the command

man -k command
 amount to
apropos command

for example
apropos passwd

Other help commands

Shell is equivalent to a shell of Linux. It is more basic than Linux and its own language

How to distinguish between self-contained commands and later added commands? Use whereis to find them. If you can find them, they are added later. If you can't find them, they are self-contained

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shell internal command help

help shell Internal command
#You can only get help from commands inside the shell

For example:
whereis cd
#Determines whether it is an internal shell command
help cd
#Get internal command help

Detailed command help info

info command
	-enter:	Enter the sub help page (with*No. (mark)
	-u:		 Enter the upper page
	-n:		 Go to the next help summary
	-p:		 Go to the previous help summary
	-q:		 t

5, Compression and decompression commands

Common compression formats: zip .gz .bz2

Common compression formats: tar.gz .tar.bz2

Compression command 1

. zip format compression and decompression

Compression:

zip Compressed file name source file
#Compressed file
zip -r Compressed file name source directory
#Compressed directory

Decompression:

unzip Compressed file
#Decompress zip file

You can also unzip the zip file in Windows

. gz format compression and decompression

Compression:

gzip source file
#Compress to gz format compressed file, the source file will disappear
gzip -c source file > Compressed file
#Compress to gz format, source file retention
#For example: 		 gzip -c cangls > cangls. gz
#gzip doesn't support this kind of - c is to print out the file and add > is to promise the file to the corresponding file

gzip -r catalogue
#Compress all sub files in the directory, but you cannot compress the directory

If the directory is compressed, it cannot compress the directory, but only the files in this directory

Decompression:

gzip -d Compressed file
#Unzip file
gunzip Compressed file
#Unzip file

. bz2 format compression and decompression

Compression:

bzip2 source file
#Compress to bz2 format, do not keep the source file
bzip2 -k source file
#Keep the original file after compression

be careful: bzip2 The command cannot compress a directory

Decompression:

bzip2 -d Compressed file
#Decompress and -k keep the compressed file

bunzip2 Compressed file
#Decompress and -k keep the compressed file

Compression Command 2

Packaging command tar

tar -cvf Package file name source file
 option:
	-c:		pack
	-v:		Display process
	-f:		Specify the packaged file name
	
for example
tar -cvf longzls.tar longzls

Unpacking:

tar -xvf Package file name
 Options:
	-x:		Unpack

for example -xvf longzls.tar

.tar.gz compression format

Actually tar.gz format is first packaged as Tar format, and then compressed into gz format

tar -zcvf Compressed package name.tar.gz source file
 Options:
	-z:		Compress to.tar.gz format
tar -zxvf Compressed package name.tar.gz
 Options:
	-x:		decompression .tar.gz format

.tar.bz2 compression format

tar -jcvf Compress enrollment.tar.bz2 source file
 option:
	-z:		Compress to.tar.bz2 format
tar -jxvf Compressed package name.tar.bz2
 Options:
	-x:		decompression .tar.bz2 format
	
	-ztvf  View without decompression

6, Shutdown and restart commands

shutdown command:
[root@localhost~]#shutdown time
 Options:
-c		Cancel the previous shutdown command
-h		Shut down
-r		restart
 Other shutdown commands:
[root@localhost~]#halt
[root@localhost~]#poweroff
[root@localhost~]#init 0
 Other restart commands:
[root@localhost~]#reboot
[root@localhost~]#init 6
 Log out:
logout

System operation level:

[root@localhost~]#runlevel
 Query the current level of the system
[root@localhost~]#cat/etc/inittab
#Modify the system default run level
id:3:initdefault:

7, Other common commands

Mount command

When inserting a u disk, you need to assign a drive letter and execute it automatically in Windows, while in Linux, you need to execute commands

1. Query and auto mount

[root@localhost~]#mount
#Query the mounted devices in the system

[root@localhost~]#mount -a
#Mount automatically according to the contents of the configuration file / etc/fstab

/etc/fstab

As long as you write this file, it will be mounted automatically
It is not recommended to write files to USB flash disk and mount them automatically. If you forget to insert USB flash disk one day, the system will crash

2. Mount command format

[root@localhost~]#mount [-t file system] [- o special options] device file name mount point

Options:
-t File system: add file system type to specify the type of mount. You can ext3,ext4,iso9660 Such file system
-o Special options: you can specify additional options to hang on

Special options:

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Cannot be easily modified:

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3. Mount CD

[root@localhost~]#mkdir/mnt/cdrom/
#Establish mount point

[root@localhost~]#mount -t iso9660 /dev/cdrom/mnt/cdrom/
#Mount CD
[root@localhost~]#mount /dev/sr0/mnt/cdrom

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The -t iso9660 in the middle can be omitted

User login view and user interaction commands

View login user information

w user name
 Command output:
USER:Login user name;
TTY:Login terminal;
FROM:From which IP Address login;
LOGIN@:Landing time;
IDLE:User idle time;
JCPU:It refers to the time occupied by all processes connected to the terminal. This time does not include the past background job time, but includes the time occupied by the currently running background job;
PCPU:It refers to the time occupied by the current process;
WHAT:Currently running commands

Query current login and past login user information

last

last Command default read/var/log/wtmp file data 
Command output
-user name
-login terminal
-Sign in IP
-Landing time
-Exit time (online time)

View the last login time of all users

lastlog

lastlog Command default read/var/log/lastlog Document content
 Command output
-user name
-Login terminal
-Sign in IP
-Last login time

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3. Mount CD

[root@localhost~]#mkdir/mnt/cdrom/
#Establish mount point

[root@localhost~]#mount -t iso9660 /dev/cdrom/mnt/cdrom/
#Mount CD
[root@localhost~]#mount /dev/sr0/mnt/cdrom

[external chain picture transferring... (img-ykleuoif-1652447802236)]

The -t iso9660 in the middle can be omitted

User login view and user interaction commands

View login user information

w user name
 Command output:
USER:Login user name;
TTY:Login terminal;
FROM:From which IP Address login;
LOGIN@:Landing time;
IDLE:User idle time;
JCPU:It refers to the time occupied by all processes connected to the terminal. This time does not include the past background job time, but includes the time occupied by the currently running background job;
PCPU:It refers to the time occupied by the current process;
WHAT:Currently running commands

Query current login and past login user information

last

last Command default read/var/log/wtmp file data 
Command output
-user name
-login terminal
-Sign in IP
-Landing time
-Exit time (online time)

View the last login time of all users

lastlog

lastlog Command default read/var/log/lastlog Document content
 Command output
-user name
-Login terminal
-Sign in IP
-Last login time