# 1 
df -h #df -h view the usage of files in the system
Size Total capacity of partition
Used Used size
Avail Remaining size
Use% Percentage used
Mounted on Path address
# 2
du -sh * View the space occupied by each file and directory in the current directory
du -sh /usr/
# 3 standards are the basis of automation
 The same software without host is placed in the same path, which is convenient for management and automation
 Now generally installed software is not placed in/usr/local I'm off

# There are a thousand orders in all
ls /usr/bin/ | wc -l
ls /usr/sbin/ | wc -l

# 5. Check which library files the command depends on
ldd /bin/ls

ls /boot
# linux kernel
# Startup mode that can be selected when starting the machine

# 1 
/etc/hosts corresponding windows C:windows/system32/drivers/etc/hosts,Hacker phishing website
# 2 test modification
yum install httpd -y
systemctl stop firewalld
echo "lqz NB" >/var/www/html/index.html
systemctl start httpd

# 1. Check the login log
cat /var/log/secure #View login time
# 2 temporary files generated by the process (360 will clean up the garbage)

# 1 sda sdb sdc sda1 sdb4
linux Medium disk file sd，The first hard disk is called a，The second one is b，sda1 Represents the first partition of the first disk, sdb4: The fourth partition of the second hard disk (the service can insert many hard disks)
# 2 /dev/null 
ls >/dev/null
# 3 /dev/random generates random numbers
echo $RANDOM
echo lqz_$RANDOM
 Create random users in batches and set passwords in batches
# 4. Keep getting data
dd if=/dev/zero of=/opt/test.txt bs=1M count=1024
'''
dd: Copy a file with a block of specified size, and perform the specified conversion at the same time.
if=File name: enter a file name. The default is standard. That is, specify the source file.< if=input file >
of=File name: the name of the output file. The default is standard output. That is, specify the destination file.< of=output file >
 bs=bytes: Set read in at the same time/The output block size is bytes Bytes.
 count=blocks: Copy only blocks Blocks, block size equal to ibs Number of bytes specified.
'''

ll /opt/test.txt
ll -h /opt/test.txt

ls /proc # You can see many id numbers, pid numbers, process numbers and unique
ls process id Folder with number
 If the process is shut down, id No. folder is gone
id No. is not unique every time it is started. Only one process is unique, systemd Is a process with process number 1. All processes are derived from it

#1 media: provides the mounting point of the device and media files
# linux has a new drive letter, which needs to be mounted manually
# Mount the data in the CD to the media directory
mount  /dev/cdrom /media/

# 2 mnt: provide mounting point of equipment (ditto)

# 3 opt: a third-party tool. The third-party software is installed by default (mysql...)

# run: the file with pid and log at the end
ls /run
cat sshd.pid  # The pid number of the process running and put it in the file
ps aux |grep sshd

# Function of. lock file, locking mechanism
# Suppose you execute now
yum install tree
# Open another window and execute the same command
yum install tree
'''
Another app is currently holding the yum lock; waiting for it to exit...
  The other application is: yum
    Memory :  71 M RSS (470 MB VSZ)
    Started: Tue Aug 18 00:26:31 2020 - 00:24 ago
    State  : Sleeping, pid: 6191
'''
cat /run/yum.pid

#Absolute path
[root@bgx /]# useradd alice
[root@bgx /]# touch /home/alice/file1
[root@bgx /]# touch ~/file2
[root@bgx /]# touch ~alice/file3

#Relative path
[root@bgx /]# mkdir abc
[root@bgx /]# touch ../file3
[root@bgx /]# touch file4
[root@bgx /]# touch abc/file5

# cd absolute path cd /etc/hostname
# CD relative path CD test / ABC CD cd ..


# cd      #Switch directories, for example: cd /etc
# cd -    #Switch back to the last directory
# cd ~    #Switch back to the current user's home directory. Note: is root different from ordinary users?
# cd .    #Represents the current directory. Generally, cp /etc/hostname is used when copying, moving, etc/
# cd ..   #Switch back to the parent directory of the current directory

# touch file                    #If there is none, it will be created; if there is one, it will be modified
# touch file2 file3
# touch /home/od/file4 file5
# touch file{a,b,c}             #{} set, equivalent touch a b c
# touch file{1..10}
# touch file{a..z}

# Options: - v show details - p create directory recursively
# mkdir dir1
# mkdir /home/od/dir1 /home/od/dir2
# mkdir -v /home/od/{dir3,dir4} 
# mkdir -pv /home/od/dir5/dir6
# mkdir -pv /home/{od/{diu,but},boy}

# Options: - L: displays the hierarchy of the directory tree
# tree /home/od/    #Displays the structure under the current directory
/home/od/
├── but
├── dir1
├── dir2
├── dir3
├── dir4
├── dir5
│   └── dir6
└── diu

#Options: - v: detailed display of operations performed by the command - r: recursive processing of directories and subdirectories - p: retention of attributes of source files or directories

# cp file /tmp/file_copy
# cp name /tmp/name         #Do not modify name
# cp file /tmp/             #Do not modify name
# cp -p file /tmp/file_p    #-p keep the attributes of the original file or directory
# cp -r  /etc/ /tmp/        #To copy a directory, you need to use the - r parameter to copy recursively
# cp -rv /etc/hosts /etc/hostname /tmp  #Copy multiple files to a directory
# cp -rv /etc/{hosts,hosts.bak}
# cp -rv /etc/hosts{,-org}

# mv file file1             #Change the name when moving in place
# mv file1 /tmp/            #Move files to tmp directory
# mv /tmp/file1 ./          #Move files from tmp directory to current directory
# mv dir/ /tmp/             #Move directory to / tmp directory

# touch file{1..3}
# mv file1 file2 file3 /opt/    #Move multiple files or to the same directory

# mkdir dir{1..3}
# mv dir1/ dir2/ dir3/ /opt     #Move multiple directories to the same directory

#Options: - r: recursion - f: forced deletion - v: detailed procedure
# rm  file.txt      #If the file alias exists, rm will delete it by default
# rm -f file.txt    #Delete files without reminding


# rm -r dir/        #You will be prompted if you delete the directory recursively
# rm -rf dir/       #Forcibly delete the directory without reminding (use with caution)


#1.rm delete example
# mkdir /home/dir10
# touch /home/dir10/{file2,file3,.file4}
# rm -f /home/dir10 / / / excluding hidden files 
# ls /home/dir10/ -a
. .. .file4


#2.rm delete example 2
# touch file{1..10}
# touch {1..10}.pdf
# rm -rf file 
# rm -rf .pdf

#------cat
# cp /etc/passwd ./pass
# cat pass      #Normal file viewing mode
# cat -n pass   #-n shows how many lines there are in the file
# cat -A pass   #Check the special symbols of the file, such as the tab key in the file
# tac pass      #View files in reverse order
cat >> test2.txt <<EOF
ads
adf
EOF

#------less,more
# less /etc/services    #Use the cursor to flip up and down, the space to turn the page, and q exit
# more /etc/services    #Use enter to scroll up and down, space to turn pages, q exit (percentage)

#------head
# head pass     #View the content of the header, the first ten lines by default
# head -n5 pass #View the first 5 lines and specify with - n
# ps aux | head -5 # Just look at the first five processes

#------tail
# tail pass  # View the end of the file. The default is 10 lines
# tail -20 /var/log/secure  # View the last 20 lines of the file
# tail -f /var/log/messages #-f dynamically view the changes at the end of the file
# tailf /var/log/messages   #View changes at the end of the file
# ps aux | tail -2

#------grep filter file content
# grep "^root" pass     #Match lines starting with root
# grep "bash$" pass     #Match lines ending in bash
# grep -i "ftp" pass    #Ignore case matching
# grep  -Ei "sync$|ftp" pass    #The matching file contains the end of sync or ftp string
# grep -n -A 2 "Failed" /var/log/secure #Match the Failed string in the / var/log/secure file and print its next 2 lines
# grep -n -B 2 "Failed" /var/log/secure #Match the Failed string in the / var/log/secure file and print its last 2 lines
# grep -n -C 2 "Failed" /var/log/secure #Match the Failed string in the / var/log/secure file and print its upper and lower lines

# Turn up, turn down
control+b: Turn down
control+f: Upturning

yum install wget -y
#Option: - O: specify download address
# wget -O /etc/yum.repos.d/CentOS-Base.repo http://mirrors.aliyun.com/repo/Centos-7.repo

# crul: browse resources on the network and -o save them locally
#Options: - o: specify download address
# curl -o /etc/yum.repos.d/CentOS-Base.repo http://mirrors.aliyun.com/repo/Centos-7.repo

# yum install lrzsz -y  #The command cannot be executed without installing the software

# rz            #Only files can be uploaded (no more than 4g)
# sz /path/file #Only files can be downloaded

# locate /etc/sh       #Search all files starting with sh in the etc directory
# locate -i /etc/sh    #Search the etc directory for all files starting with sh, ignoring case

# which ls  #Find the absolute path of ls command

# whereis ls / / find the path of the command, help manual, etc
# whereis -b ls / / only the path of the command is displayed, only binary

# For some commands related to the kernel, which whereis cannot be queried. You need to use type query
# type -a ls        #View the absolute path of the command (including aliases)
# type -a for

sort [OPTION]... [FILE]...
# -r: Reverse order - n: sort by number - t: specify the separator (default space) - k: specify the column and characters (specify 1,1,3.1,3.3)

#1. First create a file and write unordered contents
[root@lqz ~]# cat >> file.txt <<EOF
b:3
c:2
a:4
e:5
d:1
f:11
EOF

#2. Use sort to sort the output content
[root@lqz ~]# sort file.txt
a:4
b:3
c:2
d:1
e:5
f:11

#The results are not sorted by numbers, but by letters.
#You can use - t to specify the separator and - k to specify the columns to be sorted.
# -t specifies the separator and - k specifies the column, sorted by the second column
[root@lqz ~]# sort -t ":" -k2 file.txt
d:1
f:11 #Why is the second line 11? Shouldn't it be in order?
c:2
b:3
a:4
e:5

#According to the sorting method, you can only see the first character. The first character of 11 is 1. Sorting according to characters is indeed smaller than 2. 
#If you want to sort by number, you need to use the - n parameter to sort by number.
[root@lqz ~]# sort -t ":" -n -k2 file.txt
d:1
c:2
b:3
a:4
e:5
f:11


#Test cases, download files http://fj.xuliangwei.com/public/ip.txt , sort the file
[root@lqz ~]# sort -t. -k3.1,3.1nr -k4.1,4.3nr ip.txt

uniq [OPTION]... [INPUT [OUTPUT]]
#Option: - c calculate duplicate rows

#1. Create a file Txt file:
[root@lqz ~]# cat >>file2.txt <<EOF
abc
123
abc
123
EOF
#2.uniq needs to be used together with sort. First use sort sorting to make repeated contents continuous
[root@lqz ~]# cat file.txt |sort
123
123
abc
abc
#3. Use uniq to remove adjacent duplicate rows
[root@lqz ~]# cat file.txt |sort|uniq
123
abc
#4.-c parameter can count the number of repetitions of each line in the file
[root@lqz ~]# cat file.txt |sort|uniq -c
      2 123
      2 abc

cut OPTION... [FILE]...
#Options: - d specify the separator - F number, which column to take - f3,6 three columns and 6 columns - c take by character (spaces also count)
#echo "Im lqz, is QQ 306334678" >file.txt   
#Filter out the files lqz and 306334678

#Several ideas to realize the above problems
# cut -d " " -f2,5 file.txt
# cut -d " " -f2,5 file.txt |sed 's#,##g'
# sed 's#,# #g' file.txt | awk -F " " '{print $2 " " $5}'
# awk  '{print $2,$5}' file.txt |awk -F ',' '{print $1,$2}'
# awk -F  "[, ]" '{print $2,$6}' file.txt
# awk -F '[, ]+' '{print $2,$5}' file.txt

# awk fetch column
awk '{print $2,$5}' file.txt
# -F specifies the separator
awk '{print $2,$5}' file.txt | awk -F "," '{print $1,$2}'

# sed replace sed 's###g'
# sed 's###g 'fixed writing
# sed 's#,##g 'replace comma with empty
cut -d " " -f2,5 file.txt | sed 's#,##g'

wc [OPTION]... [FILE]...
#Options: - l display file lines - c Display File Bytes - w display file words

# wc -l /etc/fstab      #Count the number of lines in the / etc/fstab file
# wc -l /etc/services   #Count the line number of / etc/services file
# ls |wc -l             #Count the number of files and folders under the current path

#Extension method
# grep -n "." /etc/services  | tail -1
# awk '{print NR $0}' /etc/services | tail -1
# cat -n /etc/services  | tail -1

[root@student tmp]# cat web.log 
http://www.lqz.com/index.html
http://www.lqz.com/1.html
http://post.lqz.com/index.html
http://mp3.lqz.com/index.html
http://www.lqz.com/3.html
http://post.lqz.com/2.html

# awk -F '/' '{print $3}' web.log|sort -rn|uniq –c
# cut -d / -f3 web.log|sort -rn|uniq –c

[root@lqz ~]# ls -l ks.cfg
[root@lqz ~]# ll -h ks.cfg
-rw-------. 1 root root 4434 May 30 13:58 ks.cfg

#
-rw-------. ①:The first character is the file type, and the others are permissions
1           ②:Number of hard links
root        ③:Which user does the file belong to
root        ④:Which group does the file belong to
4434        ⑤:file size
May30 13:58 ⑥⑦⑧:Time and date of last modification
ks.cfg      ⑨:File or directory name

[root@lqz ~]# ll -d /etc/hosts /tmp /bin/ls  /dev/sda /dev/tty1 /etc/grub2.cfg /dev/log /run/dmeventd-client
-rwxr-xr-x.  1 root root 117656 Jun 30  2016 /bin/ls
srw-rw-rw-.  1 root root      0 Jan 20 10:35 /dev/log
brw-rw----.  1 root disk   8, 0 Jan 20 10:36 /dev/sda
crw--w----.  1 root tty    4, 1 Jan 20 10:36 /dev/tty1
lrwxrwxrwx.  1 root root     22 Jan 13 11:31 /etc/grub2.cfg -> ../boot/grub2/grub.cfg
-rw-r--r--.  1 root root    199 Jan 20 11:03 /etc/hosts
prw-------.  1 root root      0 Jan 20 10:36 /run/dmeventd-client
drwxrwxrwt. 61 root root   8192 Jan 21 13:01 /tmp

#explain
-   #Ordinary files (text, binary, compressed, pictures, logs, etc.) 
d   #Catalog file
b   #Device file (block device) storage device hard disk / dev/sda1, /dev/sda2
c   #Device file (character device), terminal / dev/tty1, /dev/zero
s   #Socket file, interprocess communication (socket)
p   #Pipeline file
l   #Link file

[root@lqz ~]# file /etc/hosts
/etc/hosts: ASCII text

[root@lqz ~]# file /bin/ls
/bin/ls: ELF 64-bit LSB executable, x86-64, version 1 (SYSV), dynamically linked (uses shared libs), for GNU/Linux 2.6.32, BuildID[sha1]=aa7ff68f13de25936a098016243ce57c3c982e06, stripped

[root@lqz ~]# file /dev/sda
/dev/sda: block special

[root@lqz ~]# file /dev/tty1
/dev/tty1: character special

[root@lqz ~]# file /etc/grub2.cfg
/etc/grub2.cfg: broken symbolic link to `../boot/grub2/grub.cfg'

[root@lqz ~]# file /home
/home: directory

[root@lqz ~]# file /run/dmeventd-client
/run/dmeventd-client: fifo (named pipe)

[root@lqz ~]# ll but
-rw-r--r-- 1 root root 42125 Apr  1 12:26 but
[root@lqz ~]# file but
but: Zip archive data, at least v1.0 to extract

#File soft link example
touch /root/file
ln -s /root/file /tmp/file_bak
ll /tmp/file_bak  //File under root is linked to / tmp and renamed as file_bak
  

#Directory soft link example
mkdir /soft/nginx1.1 -p
ln -s /soft/nginx1.1/ /soft/nginx
ll /soft/nginx   //View link points

#Soft link usage scenario
1.Software upgrade
2.Enterprise code release 
3.Inconvenient directory movement

#File hard link example
ln  /root/file /tmp/file_hard
ll /tmp/file_hard

#PS: hard links cannot be created in directories. Hard link files can be deleted with rm command