＊netstat
Netstat is used to display statistical data related to IP, TCP, UDP or ICMP protocols and to check the network connection status of each port of the machine.
netstat <options>, such as sudo netstat -tulpn in the above figure, displays data related to tcp and udp transport layer protocols (-tu), displays the binding port and IP information of the process that is listening or has established a connection (- ln), display the process pid and process name (-p). For example, mysqld transmits data through port 8888. It can also be written as sudo netstat -npltu.
Direct netstat --help, you can view <options> detailed information, such as -a shows all sockets included in the listening
-n directly displays the network connection with the network ip address and port.
-t Display the tcp protocol.
-l shows connections in the listening state.
-u Display udp protocol.
-p displays the process PID and process name to which the socket belongs.
sudo netstat -nplt will only display the tcp protocol and other information.
sudo netstat -nltp, display the tcp protocol, the binding port and IP information of the process being monitored , and display the pid and process name of the process. sudo netstat -natp, display the tcp protocol, the binding port and IP information of the process that is listening or has established a connection , and display the pid and process name of the process.
(Socket means socket, which is the abstraction of the endpoints for two-way communication between application processes of different hosts in the network. For example, a socket is one end of network process communication.)
＊systemctl
systemctl is the system service manager command:
(1) A certain service runs automatically after booting
eg. systemctl enable apache.service
(2) Cancel the automatic operation of a certain service
eg. systemctl disable apache.service
(3) Check whether a service runs automatically after booting
eg. systemctl is-enabled apache.service
(4) Start a service
eg. systemctl start apache.service
(5) Restart a service
eg. systemctl restart apache.service
(6) Stop a service
eg. systemctl stop apache.service
(7) Query the running status of a service
eg. systemctl status apache.service
(8) Re-download the configuration file of a service
eg. systemctl reload apache.service
(9) Prohibit a service from starting automatically or manually
eg. systemctl mask apache.service
(10) Cancel the prohibition of automatic or manual startup of a service
eg. systemctl unmask apache.service
(11) Check whether a service is activated
eg. systemctl is-active apache.service
(12) List all activated services
eg. systemctl list-units --type|-t service
(13) View all services
eg. systemctl list-units --type service --all
(14) List all failed services
eg. systemctl --failed --type=service
*echo
This command is used to output a string: echo string
You can also direct the output to a file, echo string > myfile or echo string >> myfile
*chown
The chown command can change the owner of the specified file to the specified user or group.
eg. chown root /usr/local/etc/opensips/opensips.cfg