Mycpen

Example 1
---------------------------------------------------------------------------------------------------------------------------------
menu(){
    echo "1. Monitor memory usage, if memory usage exceeds 80%, give a reminder"
    echo "2. Scan local network IPs, check which IP addresses are in use"
    echo "3. Monitor if the file /etc/passwd has been modified, check every 5 minutes"
    echo "4. Monitor if the nginx process exists, if not, give a corresponding reminder"
}

option_1(){
    total=`free -m|grep -i mem|tr -s " "|cut -d " " -f2`
    #free=`free -m|grep -i mem|tr -s " "|cut -d " " -f4`
    used=`free -m|grep -i mem|tr -s " "|cut -d " " -f3`
    used_rate=`echo "scale=4;$used/$total" |bc`
    #used_1=`echo "$total*0.8"|bc `
    result=` echo "$used_rate>0.8"|bc `
    #echo $result
    if (( $result  == 1 ))
    then
        echo -e "\e[31mUsage exceeds 80%, please expand memory in time to avoid unnecessary losses\e[0m"
    else
        echo  " nothing to do"
    fi
}

option_2(){
        for ip in `seq 255`
    do
        ( ip_full=192.168.0.$ip
        ping -c 1 $ip_full &>/dev/null && echo $ip_full >>up.txt || echo $ip_full >>down.txt
        ) &     # Note: Run in the background as a subprocess
    done
wait # Parent process waits for child processes to complete before exiting
}

option_3(){
    check_num=`diff /etc/passwd /lianxi/passwd |wc -l`
    [[ check_num -eq 0 ]] && echo "File has not been modified" || echo "File has been modified"
}

option_4(){
    pidof nginx && echo "nginx is running" || echo "nginx is down"
}

menu
read -p "Please enter your choice:" option
case $option in
1)
    option_1
    ;;
2)
    option_2
    ;;
3)
    option_3
    ;;
4)
    option_4
    ;;
*)
    echo "Please enter 1-4"
esac
Example 2: Repeat Selection
--------------------------------------------------------------------------------------------
Repeat Selection
while : 
do
done

echo "#########################"
echo "1. View memory usage"
echo "2. Scan local network IPs"
echo "3. Check if the file has been modified"
echo "4. Check nginx process"
echo "5. Exit"
echo "#########################"

while : 
do
    read -p "Please enter your choice:" options
    case $options in
    1)
    /root/shell/mem.sh
    ;;
    2)
    /root/shell/scan_ip.sh
    ;;
    3)
    /root/shell/passwd_test.sh
    ;;
    4)
    /root/shell/ngnix_test.sh
    ;;
    5)
    echo "Exiting"
    exit
    ;;
    *)
    echo "1-4"
    esac
done
--------------------------------------------------------------------------------------------
Example 3: Using awk to get
case $options in

1)
    memory_monitor(){
        total=`free -m |grep Mem |awk '{print $2}'`
        used=`free -m |grep Mem |awk '{print $3}'`
        use_rate=`echo "scale=2;$used/$total" |bc`
        result=`echo "$use_rate>0.8" |bc`
        if(( $result == 1 ))
        then
            echo "Memory usage exceeds 80%！！！"
        else
            echo "Memory usage is good!"
        fi
    }
    memory_monitor
    ;;

[root@sanchuang-linux ~]# id chenpeng			# Note: id view user and group information
uid=1030(chenpeng) gid=1030(chenpeng) group=1030(chenpeng)	
--------------------------------------------------------------------------------------------
[root@localhost ~]# useradd sanchuang
[root@localhost ~]# id sanchuang
uid=1000(sanchuang) gid=1000(sanchuang) group=1000(sanchuang)
[root@localhost ~]# less /etc/passwd
[root@localhost ~]# less /home/sanchuang/
[root@localhost ~]# passwd sanchuang
Changing password for user sanchuang.
New password:
Invalid password: Password is less than 8 characters
Re-enter new password:
passwd: All authentication tokens have been successfully updated.
[sanchuang@localhost ~]$ 		# Note: Default location after login is the user's home directory (logged in as user sanchuang)
[root@localhost ~]# less /etc/shadow			# Note: shadow stores user password information
[root@localhost ~]# less /etc/shadow
shadow   shadow-  
[root@localhost ~]# less /etc/passwd
passwd   passwd-  
[root@localhost ~]# diff /etc/passwd /etc/passwd-	# Note: passwd- backup file, each time there will be one less latest operation
21d20												# Note: Can roll back to the previous version
< sanchuang:x:1000:1000::/home/sanchuang:/bin/bash
[root@localhost ~]# diff /etc/shadow /etc/shadow-	# Note: shadowd- backup file, each time there will be one less latest operation
21d20												# Note: Can roll back to the previous version
< sanchuang:$6$dKQsah/D$6sm6owwvDEnVs8BclDWQZ7meYSaMf5Y7AofxzxwxO0PPrvzqHHVCer1G656iY2gE.sUOarUl9beKi2usYdATQ1:18571:0:99999:7:::
[root@localhost ~]# less /etc/group					# Note: Stores group information
[root@localhost ~]# less /etc/gshadow				# Note: Stores group password information

[root@localhost ~]# cd /home/sanchuang/				# Note: New user has three hidden files
[root@localhost sanchuang]# ls
[root@localhost sanchuang]# ls -al		# Note: New user account is copied from /etc/skel directory
Total usage 12
drwx------. 2 sanchuang sanchuang  62 Nov  5 10:25 .
drwxr-xr-x. 3 root      root       23 Nov  5 10:25 ..
-rw-r--r--. 1 sanchuang sanchuang  18 Apr  1 2020 .bash_logout
-rw-r--r--. 1 sanchuang sanchuang 193 Apr  1 2020 .bash_profile
-rw-r--r--. 1 sanchuang sanchuang 231 Apr  1 2020 .bashrc
[root@localhost sanchuang]# cd /etc/skel/			# Note: Template, copy one over
[root@localhost skel]# ls -al
Total usage 24
drwxr-xr-x.  2 root root   62 Oct  6 16:33 .
drwxr-xr-x. 77 root root 8192 Nov  5 10:27 ..
-rw-r--r--.  1 root root   18 Apr  1 2020 .bash_logout
-rw-r--r--.  1 root root  193 Apr  1 2020 .bash_profile
-rw-r--r--.  1 root root  231 Apr  1 2020 .bashrc

[root@localhost skel]# less /etc/login.defs		# Note: About account setting information
# Min/max values for automatic uid selection in useradd
#
UID_MIN                  1000					# Note: Up to 59000 users can be created
UID_MAX                 60000
# System accounts
SYS_UID_MIN               201
SYS_UID_MAX               999
CREATE_HOME     yes									# Note: Create home directory
ENCRYPT_METHOD SHA512								# Note: Specify the method for encrypting user passwords

[root@localhost skel]# ls /etc/group				# Note: Groups also have backup files
group   group-  
[root@localhost skel]# ls /etc/gshadow
gshadow   gshadow-  

[root@localhost spool]# cd /var/spool/mail/			# Note: Mail directory
[root@localhost mail]# ls							# Note: Create a file with the same name under /var/spool/mail/
sanchuang

[sanchuang@localhost ~]$ less /etc/shadow			# Note: Ordinary users do not have permission to view /etc/shadow which stores password information
/etc/shadow: Permission denied								 # Note: Only root user can read

[root@localhost mail]# cat /etc/passwd
root:x:0:0:root:/root:/bin/bash
bin:x:1:1:bin:/bin:/sbin/nologin
sanchuang:x:1000:1000::/home/sanchuang:/bin/bash
·Use: Separator
·Field 1: Username
·Field 2: Password placeholder, usually "x" or "*" (because this file is readable by anyone, the actual password is stored in /etc/shadow)
·Field 3: User ID							# Note: -u specifies
·Field 4: User's primary group ID					 # Note: -g specifies primary group
·Field 5: User description information						  # Note: New users generally do not set this (no -c option)
·Field 6: Home directory							# Note: Absolute path of home directory			(-d option)
·Field 7: Login shell information

Example
--------------------------------------------------------------------------------------------
[root@localhost ~]# ls -ld /etc/shadow
----------. 1 root root 2330 Nov  5 20:51 /etc/shadow		# Note: Ordinary users/groups cannot read or execute
[root@localhost ~]# ls -ld /etc/passwd
-rw-r--r--. 1 root root 2006 Nov  5 20:51 /etc/passwd

#Note: Configuration files installed through yum are generally placed in /etc

[root@sanchuang-linux ~]# awk -F: '$3>1000{print $1,$3,$6,$7}' /etc/passwd
chenpeng 1030 /home/chenpeng /bin/bash

#Note: Using cat and directly using awk consumes similar memory
#Note: Syntax: awk options 'pattern+action' file		# Note: If no pattern is specified, the entire text is captured

Shell Settings
[root@sanchuang-linux ~]# awk -F: '{print $7}' /etc/passwd |sort|uniq		# Note: Sort and remove duplicates
/bin/bash		# Note: System default user shell environment information --> Normal shell used
/bin/sync		# Note: Flush the cache in memory to disk --> Similar to Python's fp.flush()
/sbin/halt		# Note: Shut down upon login
/sbin/nologin	# Note: User cannot log in (not allowed to log in)

--------------------------------------------------------------------------------------------
#Note: The shutdown command will execute sync to flush the cache in memory to disk
[root@localhost ~]# sync
--------------------------------------------------------------------------------------------
#Note: Use the which command to view the absolute path of the command
[root@localhost ~]# which sync
/usr/bin/sync
Executing a command in /bin/bash will take us to our current terminal environment.

/bin/bash			# Note: System default user shell environment information --> Normal shell used
/bin/sync			# Note: Flush the cache in memory to disk --> Similar to Python's fp.flush()
/sbin/halt			# Note: Shut down upon login
/sbin/nologin		# Note: User cannot log in, neither ssh nor su can log in
/sbin/shutdown		# Note: Shut down upon login

Example: -s /sbin/nologin
--------------------------------------------------------------------------------------------
#Note: This machine is used to run services, cannot log in
[root@localhost mail]# useradd -s /sbin/nologin sanchuang2
[root@localhost mail]# echo 123456|passwd sanchuang2 --stdin
Changing password for user sanchuang2.
passwd: All authentication tokens have been successfully updated.
[root@localhost mail]# ssh sanchuang2@192.168.136.136	#Note: ssh login to local sanchuang2
……………………………………
Are you sure you want to continue connecting (yes/no)? yes
Warning: Permanently added '192.168.136.136' (ECDSA) to the list of known hosts.
sanchuang2@192.168.136.136's password: 
This account is currently not available.	# Note: Prompt user is unreachable, because sanchuang2's shell is nologin, cannot log in directly
Connection to 192.168.136.136 closed.
[root@localhost ~]# su - sanchuang2			# Note: Cannot switch
Last login: Thu Nov  5 11:49:14 CST 2020 from 192.168.136.136pts/2
This account is currently not available.
--------------------------------------------------------------------------------------------
[root@localhost ~]# usermod -s /bin/bash sanchuang2		# Note: usermod -s change user's shell information
[root@localhost ~]# cat /etc/passwd|grep sanchuang2
sanchuang2:x:1001:1001::/home/sanchuang2:/bin/bash

[root@localhost ~]# awk -F: '$3>1000{print $1,$3,$6}' /etc/passwd
sanchuang2 1001 /home/sanchuang2
Method 1
[root@localhost ~]# awk -F: '$3>1000{print $1,$3,$6}' /etc/passwd |grep sanchuang
sanchuang2 1001 /home/sanchuang2
Method 2
[root@localhost ~]# awk -F: '$3>1000 && $1 ~ /sanchuang/{print $1,$3,$6}' /etc/passwd
sanchuang2 1001 /home/sanchuang2			# Note: $1 ~ /sanchuang/ matches sanchuang

>>> import os
>>> os.geteuid()					# Note: Get the current process user's UID information
0									# Note: 0 indicates root user
>>> os.getuid()						# Note: Usually, uid and euid are the same
0
--------------------------------------------------------------------------------------------
Ordinary user importing os module
[sanchuang2@localhost ~]$ python3
>>> import os
>>> os.geteuid()
1001
>>> os.getuid()
1001
[sanchuang2@localhost ~]$ id sanchuang2
uid=1001(sanchuang2) gid=1001(sanchuang2) group=1001(sanchuang2)

============================================================================================
1. Service Installation
[root@sanchuang-linux ~]# yum install vsftpd
--------------------------------------------------------------------------------------------
2. Start Service
[root@sanchuang-linux ~]# service vsftpd restart
Redirecting to /bin/systemctl restart vsftpd.service
[root@sanchuang-linux ~]# ps -ef |grep vsftp			# Note: Default root user starts
root        3377       1  0 14:51 ?        00:00:00 /usr/sbin/vsftpd /etc/vsftpd/vsftpd.conf
root        3379    3184  0 14:52 pts/1    00:00:00 grep --color=auto vsftp
--------------------------------------------------------------------------------------------
3. Install Client
#Note: In CentOS 8, vsftpd service does not allow anonymous users to log in by default
    To use anonymous user (ftp) to log in, modify the configuration in /etc/vsftpd/vsftpd.conf to anonymous_enable=YES
#Note: Restart the vsftpd service after modifying the configuration

After logging in, it will read the home directory files of the ftp user in the system by default
-----------------------------------------------------
[root@sanchuang-linux ~]# yum install lftp -y			# Note: lftp is the client for vsftpd
[root@sanchuang-linux ~]# yum install ftp	-y			# Note: ftp is also the client for vsftpd
#Note: Both are FTP clients
============================================================================================
[root@sanchuang-linux ~]# lftp ftp@192.168.0.27		# Note: Log in as ftp user
Password: 											   # Note: ftp is the default user
[root@localhost ~]# ftp 192.168.136.136				# Note: Log in to FTP service
………………………………
Name (192.168.136.136:root): ftp					# Note: Anonymous user ftp login
331 Please specify the password.
Password:											# Note: Press Enter
230 Login successful.
………………………………
ftp> 
============================================================================================
[root@localhost ~]# cat /etc/passwd
ftp:x:14:50:FTP User:/var/ftp:/sbin/nologin			# Note: vsftpd's anonymous user, public user
#Note: /var/ftp is the home directory file for the ftp user
============================================================================================
[root@localhost ~]# vim /etc/vsftpd/vsftpd.conf 	# Note: Enable anonymous user login in CentOS 8
anonymous_enable=YES									# Note: Not needed in CentOS 7
#Note: Restart the vsftpd service after modifying the configuration
============================================================================================
After logging in, it will read the home directory files of the ftp user in the system
/var/ftp
-----------------------------------------------------
[root@localhost ~]# cd /var/ftp/
[root@localhost ftp]# ls
pub
[root@localhost ftp]# cd pub
[root@localhost pub]# ls					# Note: /var/ftp/pub/ is empty
[root@localhost pub]# touch aa bb			# Note: Create files aa bb
--------------------------------------------------------------------------------------------
ftp> ls										# Note: Current path /var/ftp
………………………… 
drwxr-xr-x    2 0        0              26 Nov 05 07:20 pub
ftp> cd pub
………………………… 
ftp> ls										# Note: Display files aa bb
………………………… 
-rw-r--r--    1 0        0               0 Nov 05 07:20 aa
-rw-r--r--    1 0        0               0 Nov 05 07:20 bb
226 Directory send OK.
--------------------------------------------------------------------------------------------
ftp> get aa									# Note: Download file
local: aa remote: aa
………………………… 
ftp> !ls									# Note: View current system command files
aa	 addstr.py
ftp> !pwd									# Note: View current system command path
/root
#Note: Anonymous users cannot upload
============================================================================================
[root@localhost ~]# ftp 192.168.136.136
Name (192.168.136.136:root): sanchuang		# Note: Local user sanchuang logs in
Password:
230 Login successful.						# Note: 230 indicates login successful
--------------------------------------------------------------------------------------------
ftp> put first.py 							# Note: Upload file
local: first.py remote: first.py			# Note: Anonymous users cannot upload
………………………… 
1097 bytes sent in 0.0157 secs (69.83 Kbytes/sec)
ftp> ls
………………………… 
-rw-r--r--    1 1000     1000         1097 Nov 05 07:34 first.py
226 Directory send OK.
============================================================================================
[root@localhost pub]# less /etc/services 		# Note: # less /etc/services to view default port number
ftp             21/tcp							# Note: FTP service default is port 21
ftp             21/udp          fsp fspd

Example
--------------------------------------------------------------------------------------------
[root@localhost ~]# useradd stu01  
[root@localhost ~]# ls -ld /home/stu01/
drwx------ 2 stu01 stu01 4096 09-09 12:38 /home/stu01/  
[root@localhost ~]# userdel -r stu01				# Note: Delete user account stu01
[root@localhost ~]# ls -ld /home/stu01/  
ls: /home/stu01/: No such file or directory

Example: mysql uid
--------------------------------------------------------------------------------------------
[root@localhost ~]# id mysql
uid=1000(mysql) gid=1000(mysql) group=1000(mysql)
[root@localhost ~]# id sanchuang2
uid=1001(sanchuang2) gid=1001(sanchuang2) group=1001(sanchuang2)

Example
--------------------------------------------------------------------------------------------
#Note: By default, if no uid is specified, it will increment by 1 from the previous user
[root@localhost ~]# useradd -u 1100 chenpeng1			# Note: Specify user ID
[root@localhost ~]# id chenpeng1
uid=1100(chenpeng1) gid=1100(chenpeng1) group=1100(chenpeng1)
[root@localhost ~]# useradd -u 1101 -g 1100 chenpeng2	# Note: Specify user ID, primary group
[root@localhost ~]# id chenpeng2						# Note: Inside the chenpeng1 group
uid=1101(chenpeng2) gid=1100(chenpeng1) group=1100(chenpeng1)

Example
--------------------------------------------------------------------------------------------
[root@localhost ~]# usermod -u 1200 chenpeng2			# Note: Modify user ID
[root@localhost ~]# id chenpeng2
uid=1200(chenpeng2) gid=1100(chenpeng1) group=1100(chenpeng1)

Example
--------------------------------------------------------------------------------------------
[root@localhost ~]# useradd -d /var/log/sanchuang6 sanchuang6	# Note: Specify user home directory
[root@localhost ~]# cd /var/log/sanchuang6/
[root@localhost sanchuang6]# ls
[root@localhost sanchuang6]# less /etc/passwd
sanchuang6:x:1201:1201::/var/log/sanchuang6:/bin/bash			# Note: Column 6 is the user's home directory

Example: Specify supplementary group
--------------------------------------------------------------------------------------------
[root@localhost sanchuang6]# useradd -g chenpeng1 -G sanchuang,sanchuang2 sanchuang7
[root@localhost sanchuang6]# id sanchuang7
uid=1202(sanchuang7) gid=1100(chenpeng1) group=1100(chenpeng1),1000(sanchuang),1001(sanchuang2)
#Note: Primary group chenpeng1  Supplementary groups sanchuang  sanchuang2
#Note: -g specifies primary group  -G specifies supplementary groups
============================================================================================
·-c: User comment description information
You can check the description information in the 5th column of /etc/passwd

Example 1
--------------------------------------------------------------------------------------------
[root@localhost ~]# useradd stu01  
[root@localhost ~]# ls -ld /home/stu01/
drwx------ 2 stu01 stu01 4096 09-09 12:38 /home/stu01/  
[root@localhost ~]# userdel -r stu01						# Note: Delete user account stu01
[root@localhost ~]# ls -ld /home/stu01/  
ls: /home/stu01/: No such file or directory

Example 2
--------------------------------------------------------------------------------------------
[root@localhost sanchuang6]# userdel sanchuang7
[root@localhost sanchuang6]# less /etc/passwd				# Note: Deleted
[root@localhost sanchuang6]# cd /home/sanchuang7			# Note: Not deleted
[root@localhost sanchuang7]# ls /var/spool/mail/sanchuang7	# Note: Not deleted
/var/spool/mail/sanchuang7

Example: -L: Lock the user account
--------------------------------------------------------------------------------------------
#Note: After locking, cannot log in with password
#Note: Essentially adds a ! in front of the shadow password, causing password verification to fail during login
[root@localhost sanchuang7]# id sanchuang6
uid=1201(sanchuang6) gid=1201(sanchuang6) group=1201(sanchuang6)
[root@localhost sanchuang7]# usermod -L sanchuang6		# Note: Lock the user account
[root@localhost sanchuang7]# less /etc/shadow			# Note: A ! has been added in front of the password ciphertext
chenpeng2:!$6$P3yFUy.H$UOfUIbl8V3h1ng4J/OdVV1aWc3Cx3s5bldkysl33aDyrigsgK0VQ3nzrC4mojDNotpE9w61NbVQmZFqDDRfpl.:18571:0:99999:7:::
[root@localhost sanchuang7]# diff /etc/shadow /etc/shadow-
25c25
< chenpeng2:!$6$P3yFUy.H$UOfUIbl8V3h1ng4J/OdVV1aWc3Cx3s5bldkysl33aDyrigsgK0VQ3nzrC4mojDNotpE9w61NbVQmZFqDDRfpl.:18571:0:99999:7:::
---
> chenpeng2:$6$P3yFUy.H$UOfUIbl8V3h1ng4J/OdVV1aWc3Cx3s5bldkysl33aDyrigsgK0VQ3nzrC4mojDNotpE9w61NbVQmZFqDDRfpl.:18571:0:99999:7:::
#Note: SHA512 encryption technology  Ciphertext Plaintext
--------------------------------------------------------------------------------------------
[root@localhost ~]# ssh chenpeng2@192.168.0.188
chenpeng2@192.168.0.188's password: 					# Note: Cannot log in with password after locking
Permission denied, please try again.
………………………… 
Permission denied (publickey,gssapi-keyex,gssapi-with-mic,password).

Example
--------------------------------------------------------------------------------------------
[root@localhost sanchuang7]# passwd -d sanchuang6		# Note: Clear user password
Clearing password for user sanchuang6.
passwd: Operation successful
[root@localhost sanchuang7]# useradd sanchuang5			# Note: Register without giving a password
[root@localhost mail]# less /etc/shadow
sanchuang6::18571:0:99999:7:::							# Note: Clearing user password leaves the password field empty
sanchuang5:!!:18571:0:99999:7:::						# Note: No password given, the password field defaults to two exclamation marks

#usermod and passwd locking accounts both modify the shadow encrypted field information of the account, causing them to fail to match during login, achieving a locked state
#usermod -L   adds a ! in front of the user's shadow password field				# Note: Locking the user adds a ! in front of the shadow password field
#passwd -l 	adds two ! in front of the user's shadow password field				# Note: Locking the user adds two ! in front of the shadow password field
#Note: To check if a user has set a password, check the /etc/shadow information

Example: usermod -L and passwd -l	Lock User
--------------------------------------------------------------------------------------------
[root@localhost mail]# useradd chen001
[root@localhost mail]# useradd chen002
[root@localhost mail]# useradd chen003
[root@localhost mail]# echo 123456|passwd chen001 --stdin
[root@localhost mail]# echo 123456|passwd chen002 --stdin
[root@localhost mail]# echo 123456|passwd chen003 --stdin
[root@localhost mail]# usermod -L chen002				# Note: Perform usermod -L operation on chen002
[root@localhost mail]# passwd -d chen003				# Note: Perform passwd -d operation on chen003
Clearing password for chen003.
passwd: Operation successful
[root@localhost mail]# less /etc/shadow
chen001:$6$y……k1q.yk8U1gOGp/:18571:0:99999:7:::
chen002:!$6$u……YF0.:18571:0:99999:7:::
chen003::18571:0:99999:7:::
------------------------------------------------------------------------
[root@localhost ~]# ssh chen003@192.168.136.136			# Note: Cannot log in
chen003@192.168.136.136's password: 
…………
Permission denied (publickey,gssapi-keyex,gssapi-with-mic,password).
[root@localhost ~]# ssh chen002@192.168.136.136			# Note: Cannot log in
chen002@192.168.136.136's password: 
…………
Permission denied (publickey,gssapi-keyex,gssapi-with-mic,password).
[root@localhost ~]# ssh chen001@192.168.136.136			# Note: No operations performed, remote login successful
chen001@192.168.136.136's password: 
[chen001@localhost ~]$ 

Example
--------------------------------------------------------------------------------------------
[root@localhost ~]# less /etc/group
tech:x:200:b1,b2,a1,a2