Unlock blacklist

What is a blacklist?

Blacklist is a security or management mechanism used to restrict specific users, devices or IP addresses from accessing certain resources or services. Blacklists are typically used to prevent unauthorized access, filter inappropriate content, block malicious attacks, or protect system security.

Why do you need to unlock the blacklist?

Sometimes, legitimate users or devices may be blacklisted due to misidentification. Unlocking the blacklist allows normal usage rights to be restored. Common situations that require unlocking the blacklist include:

• Misjudgment:Users' IP addresses or accounts may be blacklisted due to false positives or disguised behavior.
• Account recovery:If a user has been blocked but the problem has been resolved, they can resume use after being unlocked.
• Security policy adjustments:As security policies or system requirements change, some previously blocked objects may no longer be a threat.

Steps to unlock blacklist

Here are the general steps to unlock the blacklist:

1. Find the blacklist management system:Confirm the blacklist management functions of the system or service, such as firewall, website management background or application settings.
2. Find blocked objects:Check the blacklist entries to find the IP address, user, or device that needs to be unlocked.
3. To perform the unlocking operation:Remove the entry from the blacklist or unblock it in the blacklist management interface.
4. Re-verify:After unlocking, confirm that the user or device can access restricted resources normally to ensure successful unlocking.

Things to note when unlocking the blacklist

• Keep it safe:Before unlocking, make sure that the unlocked object does not pose a security threat to the system.
• Record changes:Keep records of unlocking so that you can trace back or review blacklist change records in the future.
• Regular inspection:Check and update blacklists regularly to avoid blocking legitimate users or devices for long periods of time.

in conclusion

The setting of the blacklist helps to improve the security of the system, but in some cases it may also block legitimate objects by mistake. Unlocking the blacklist is an important means to repair these misjudgments. Properly managing the blacklist and unlocking process can provide a smooth user experience while protecting security.

Reverse DNS settings

Reverse DNS (rDNS) setting is the process of resolving an IP address back to its corresponding domain name. This is the opposite of Forward DNS, which resolves domain names into IP addresses. Properly configuring rDNS is very important for mail servers, network security, and log analysis.

The importance of rDNS settings

• Mail server reputation:Many mail servers check the sending server's rDNS records to verify its identity. If the rDNS record does not match or does not exist, the message may be marked as spam or rejected.
• Internet Security:rDNS can be used to confirm the identity of devices connected to your service.
• Log analysis:In server logs, the domain name can be displayed instead of just the IP address, making the logs easier to read and analyze.

rDNS setup steps

rDNS records (PTR records) are usually represented byThe organization that owns the IP address(for example, your Internet Service Provider (ISP) or cloud service provider) to set up and manage it, rather than managing your primary DNS server yourself.

1. Determine the IP address

Confirm the server you want to configure rDNS forPublic static IP address.例如：$192.0.2.10$。

2. Determine the corresponding domain name (FQDN)

Determines what the IP address should resolve toFull domain name (FQDN). This FQDN is usually your server hostname. For example:mail.example.com。

3. Set up A records on your forward DNS server

Make sure you have set up a DNS server for your domain nameA record, point the FQDN of your choice to that IP address. This is a prerequisite for rDNS to operate correctly.

mail.example.com. IN A 192.0.2.10

4. Contact your IP provider

Contact your ISP, cloud service provider (such as AWS, GCP, Azure) or hosting company and ask them to set one for your IP addressPTR record, point it to the FQDN you determined in step 2 (mail.example.com)。

they will be thereReverse parsing areaCreate a record in:

10.2.0.192.in-addr.arpa. IN PTR mail.example.com.

(Note that IP addresses are inverted in the reverse resolution zone.)

5. Verify settings

After the PTR record takes effect (may take some time, depending on the vendor), you can usedig -xornslookupWait for the command to verify whether the rDNS settings are correct.

dig -x 192.0.2.10

The expected result should show the PTR record asmail.example.com。

No matching A record exists for reverse DNS

When "Reverse DNS (rDNS)" does not match "Forward DNS", it means that although your IP address has a PTR record pointing to a domain name (FQDN), the FQDN does not have an A record (or AAAA record) pointing to the IP address, which will lead to verification failure, commonly known asrDNS check failedorrDNS/A record mismatch。

🚨 Causes and effects

Cause:

This is usually because the setup process is only half complete. You set up a PTR record with your IP provider (ISP/cloud service provider), but forgot or mistakenly set up a corresponding A record with the DNS provider that manages your domain name.

• A record not set:The A record for $FQDN \rightarrow IP$ is missing on your domain name DNS server.
• A record IP error:The A record points to the wrong IP address (does not match the IP to which the PTR record belongs).
• Wrong domain name:The FQDN pointed to by the PTR record is written incorrectly and is inconsistent with the FQDN of the A record.

Main impact:

rDNS check failures most severely impact the following services:

• Mail server (SMTP):Most email service providers (such as Gmail, Outlook, etc.) perform rDNS checks. If there is no match, the message will beRejectOr throw it directly intoSpam, seriously affecting email delivery rate and server reputation.
• FTP/SSH service log:Some servers perform rDNS lookups on connection, and a mismatch may cause connection delays or the domain name not being displayed correctly in the logs.

🔧 Solution steps: Ensure bidirectional consistency

The key to solving this problem is to ensure that the "positive solution" and the "anti-solution" are completely consistent.Two-way consistency（Bi-directional Consistency）。

Step 1: Check PTR records (Reverse DNS)

First, confirm what domain name is currently being resolved to your IP address. You'll need to use a web tool to query your IP provider's DNS servers.

• Tool instructions:

  dig -x your IP address

• result:Assume that the query results show that the PTR record is:mail.example.com。

Step 2: Check A records (forward DNS)

Next, check that the A record you set up on your domain name server (Domain Registrar or DNS provider) matches the FQDN from step 1 and points to the correct IP.

• Tool instructions:

  dig A mail.example.com

• result:A record IPmustis your server IP address. If the A record does not exist, the A record points to a different IP address, or the FQDN you query is written incorrectly, it needs to be corrected.

Step 3: Fix and ensure consistency

Make corrections based on your findings in steps 1 and 2:

• If A record is wrong:Log in to your domain DNS management interface formail.example.comCreate or modify an A record so thatPoint to your exact server IP address。
• If the PTR logs errors:Contact your IP provider (such as HiNet) and ask them to record the PTR for the IPCorrect to the FQDN your A record points to(Right nowmail.example.com)。

Step 4: Final verification

Wait for the DNS cache update time (TTL) to pass and repeat steps 1 and 2. The problem is solved when both query results are correct and match each other.

• dig -x your IP$\rightarrow$ must be displayedmail.example.com
• dig A mail.example.com$\rightarrow$ must be displayedyour IP address

IP decryption settings for Hinet DNS service

Chunghwa Telecom's (HiNet) reverse DNS (Reverse DNS, rDNS) service, often called "IP reverse resolution service", is mainly provided toHiNet fixed broadband Internet customers. The setting process is carried out through HiNet's exclusive service management platform, rather than directly operating in the DNS hosting setting interface.

Service objects and setting conditions

• Service objects:Only HiNet fixed broadband Internet accessFixed IP address. Floating IP or non-HiNet IP cannot be set.
• Service content:Each fixed IP can be set with a corresponding PTR record (Pointer Record).
• Important prerequisites:You must ensure that the IP address corresponds toFull domain name (FQDN), you have set up a correct one in your DNS server or HiNet DNS hosting service.A record (Address Record)Point to this fixed IP. The reverse solution record and the correct solution record must be consistent.

Hinet IP decryption service setting steps

Setting up IP decryption is done through Chunghwa Telecom’s “EyeSee” or enterprise customer service platform. The steps are as follows:

1. Log in to the enterprise customer service platform

• Use your HiNet enterprise customer account to log in to Chunghwa Telecom’s"EyeSee" service platformOr the relevant "Broadband Internet Value-added Service" management interface.

2. Enter value-added service management

• Find and select the platform"Broadband Internet"Related service options, usually including"Value-added Service Management"or"DNS Service Management"。
• In the list of circuits displayed, select the one for which you want to set a fixed IPfixed circuit。

3. Select IP decryption settings

• After entering the management page of the circuit, look for"IP decryption setting"or"PTR Record Settings"option and click.

4. Create or modify PTR records

• All fixed IP addresses under this fixed circuit will be listed.
• Select the IP address for which you want to set up decryption.
• In the designated field, enter the IP address that should be decoded toFull domain name (FQDN). For example:server.yourcompany.com。
• Please note:Many HiNet interfaces require the FQDN to end with a dot (.),For exampleserver.yourcompany.com.。
• After confirming that the input is correct, save and send the settings.

5. Verification and Effective Time

• It can take several hours for HiNet to process PTR records before they become effective. It is recommended to wait patiently after setting up.
• You can use web tools such asnslookupordig) to verify the settings:

  dig -x your fixed IP address

  If successful, the results will show the FQDN you set as the value of the PTR record.

Special case: Authorization of the entire Class C IP

If you have HiNet subscriptionEntire Class C segmentFor customers (for example, $/24$ network segment), you can apply to Chunghwa Telecom for the IP decryption and management rights of this network segment.DelegateDNS servers assigned to you. Once the authorization is completed, you can manage the PTR records of all IPs in the network segment on your own DNS server without having to set them one by one through the HiNet platform.

nslookup queries reverse DNS and consistency

nslookupIt is a common network management tool on Windows, macOS and Linux that can be used to query DNS server records. Althoughdigis a more modern and professional tool, butnslookupCan still be used to quickly check forward DNS (A records) and reverse DNS (PTR records) consistency.

1. Query forward DNS (A record)

First, you need to query the IP address corresponding to the domain name. This is the first step in ensuring that the correct answer exists and is correct.

Query steps:

1. Open Command Prompt (Windows) or Terminal (macOS/Linux).
2. enternslookupEnter interactive mode, or enter the domain name directly after the command.

Command example:

nslookup mail.example.com

Expected results:

The result should return the IP address corresponding to the domain name. Make a note of this IP address, it will be the target of your next check for reverse DNS.

Server: [your DNS server IP]
Address: [your DNS server IP]#53

Non-authoritative answer:
Name: mail.example.com
Address: 192.0.2.10 <-- Note this IP

2. Query reverse DNS (PTR record)

Next, use the IP address you obtained in step 1 to query the domain name decoded from the IP address. This is the process of querying PTR records.

Query steps:

existnslookup, directly enter the IP address to perform a reverse query.

Command example:

nslookup 192.0.2.10

Expected results:

The result should return the domain name corresponding to the IP address.

Server: [your DNS server IP]
Address: [your DNS server IP]#53

Non-authoritative answer:
10.2.0.192.in-addr.arpa name = mail.example.com. <-- This is the result of the PTR record

3. Check forward and reverse consistency

DNS consistency checking (or Bi-directional Consistency) is a critical step in ensuring server reputation. If the forward and reverse are inconsistent, it will usually cause the mail server to refuse the connection.

Consistency judgment criteria:

• Forward query results (FQDN from step 1): mail.example.com
• Reverse query results (PTR record from step 2): mail.example.com

If the domain name of both resultsexactly the same, it means that the DNS is set correctly and consistent.

Inconsistent examples:

• Forward query (A record): mail.example.com $\rightarrow$ 192.0.2.10
• Reverse lookup (PTR record): 192.0.2.10 $\rightarrow$ hinet-user-192-0-2-10.hinet.net(not the FQDN you expected)

In this case, the reverse DNS is inconsistent with the forward DNS and you need to contact your IP provider (e.g. HiNet) to modify the PTR record so that it points tomail.example.com。

Telnet

Agreement Overview

Telnet (Telecommunication Network) is an application layer network protocol that uses the TCP/IP protocol family to allow users to connect to remote hosts through the network and provide a two-way, interactive text-oriented communication facility. It is one of the earliest protocols of the Internet, and the standard port number is 23.

How it works

• The client and server establish a session through TCP connection.
• The Telnet protocol defines a set of Network Virtual Terminal (NVT) standards to ensure communication between different operating systems and terminal types.
• The user's input on the local terminal will be sent to the remote host for execution, and the output of the remote host will be sent back to the local terminal for display.
• Communication content includes data and control functions (such as negotiation options).

Main functions

• Remote login: Allows users to remotely control another computer and execute commands and programs.
• Network service testing: Since Telnet directly uses plain text communication, it is often used to manually test other text-based protocol services, such as SMTP, HTTP, etc., to check whether the service is functioning properly.

Security risks and alternatives

When Telnet transmits data, including user name and password, it is transmitted over the network in the form of unencrypted plain text. This makes the data vulnerable to sniffing, causing serious security risks. Therefore, when remote secure connections are required, Telnet has been replaced by more secure protocols. The most common alternative is SSH (Secure Shell), which provides encrypted communication to ensure data security.

Commonly used Telnet commands (client)

SSH

Introduction to the agreement

SSH (Secure Shell) is a network protocol used to provide secure data communication and remote operation services in an insecure network environment. It is designed to replace insecure protocols such as Telnet, rlogin and FTP. It protects the connection between the client and the server through encryption, ensuring that all transmitted data will not be eavesdropped or tampered with. The standard port number for SSH is 22.

Main functions and advantages

• Secure remote login: Provides an encrypted remote command line interface (CLI), allowing users to securely control the server.
• Data encryption: All data transmitted in the SSH connection, including username, password and command output, will be encrypted.
• Data integrity: Use hashing algorithm (Hashing) to ensure that the data in transmission has not been maliciously modified.
• Authentication mechanism: Supports a variety of powerful authentication methods, including password authentication, public key authentication (Public Key Authentication), etc.
• Port Forwarding and Tunneling: Allow SSH connections to securely transmit data of other network protocols, such as establishing a secure VPN tunnel, or securely transmitting data of graphical interface applications (such as X11).

SSH architecture

The SSH protocol consists of three main layers:

1. Transport Layer Protocol: Responsible for providing server authentication, data encryption and data integrity.
2. User Authentication Protocol: Responsible for verifying the user's identity to the server.
3. Connection Protocol: Responsible for multiplexing encrypted communication channels into multiple logical channels for shell sessions, port forwarding, etc.

Public key authentication mechanism

Public key authentication is one of the most secure login methods for SSH. It works as follows:

1. The user generates a pair of keys on the local client: a private key (Private Key) and a public key (Public Key).
2. Copy the public key to the authorized key file on the remote server (usually~/.ssh/authorized_keys）。
3. When the client attempts to connect, the server challenges the client using the stored public key.
4. The client responds to the challenge using its private key, proving its identity. The private key never leaves the client, ensuring a high level of security.

Comparison with Telnet

SSH Tunnel

Definitions and Concepts

SSH Tunneling (or SSH Port Forwarding) is a technology that uses SSH protocol encrypted channels to transmit other network service data. It allows users to securely forward traffic from one network port to another network port or host through an SSH connection. This is primarily used to bypass firewall restrictions, encrypt unencrypted application traffic, or access hosts and services restricted to the local network.

SSH Tunnel Type

There are three main types of SSH port forwarding: local, remote, and dynamic.

1. Local Port Forwarding

• use:Forward the local machine's port to a target host and port accessible to the remote SSH server.
• Scenario:Used to securely access internal network services behind firewalls.
• Format: ssh -L [localport]:[destination host]:[destination port] [SSH server]
• Operation:The client opens a local port, and all traffic sent to this port will be encrypted, sent to the SSH server (Server) through the SSH channel, and then decrypted by the server and forwarded to the final target host (Destination).

2. Remote Port Forwarding

• use:Forward the port on the remote SSH server to the target host and port that is accessible to the local machine.
• Scenario:Allows external users to access local services behind the firewall through the SSH server.
• Format: ssh -R [remote port]:[destination host]:[destination port] [SSH server]
• Operation:The server opens a remote port. All traffic sent to this port will be encrypted and sent to the client through the SSH channel. The client will then decrypt and forward it to the final target host (Destination).

3. Dynamic Port Forwarding

• use:Configure the SSH client as a SOCKS proxy server (SOCKS Proxy).
• Scenario:Used to establish a secure Internet browsing channel to bypass network censorship or restrictions. All applications (such as browsers) that support the SOCKS protocol can communicate through this proxy.
• Format: ssh -D [localport] [SSH server]
• Operation:The client opens a local SOCKS port. After the application configures this port, all requests will be dynamically sent to the SSH server (Server) through the SSH channel, and the server will then connect to any host on the Internet based on the destination of the request.

Security and applications

The core value of SSH Tunneling is its security. Since the entire transmission process is encapsulated in the SSH encryption layer, data can be protected even on public Wi-Fi or other unsecured networks, preventing man-in-the-middle attacks and data eavesdropping. It is widely used in scenarios such as system administrators accessing intranet resources, developers conducting testing, and general users establishing personal encrypted channels.

Remote monitoring and management (RMM)

definition

Remote Monitoring and Management (RMM) is an IT tool or platform that allows technicians to remotely monitor, maintain and manage dispersed IT assets and terminal devices. It is often used by managed service providers (MSP) or the IT departments of large enterprises.

Main functions

• Equipment health status monitoring
• Automated remediation and script execution
• Remote desktop support
• Patch management and software updates
• Asset and hardware and software inventory management
• Security monitoring and warning notifications

Application scenarios

• IT support outsourcing for small and medium-sized enterprises
• Branch office and remote worker management
• Data center and server farm monitoring
• IT compliance and audit support

advantage

• Instantly understand device status and problems
• Reduce on-site support needs and labor costs
• Improve IT resource management efficiency
• Strengthen information security and compliance

challenge

• Need to deal with multi-platform and multi-device compatibility
• Data transmission and remote connection security issues
• Initial setup and system maintenance are complicated
• User privacy concerns about remote access

remote desktop

concept

Remote Desktop is a technology that allows users to log in and operate another computer from a remote device. Common uses include remote working, system maintenance, technical support, etc.

Common tools

• Windows Remote Desktop (RDP)：Built into Windows system
• AnyDesk: Lightweight and fast, supports cross-platform, and can be used for personal and commercial purposes
• TeamViewer:Support remote control and file transfer
• Chrome Remote Desktop: Browser extensions operated with a Google Account
• VNC: Cross-platform remote protocols, such as RealVNC, TightVNC

Tool pros and cons comparison

Windows Remote Desktop (RDP)

1. How to enable:
   • "Settings" → "System" → "Remote Desktop" → Enable
2. Set allowed accounts and firewall rules
3. usemstscOpen the remote desktop and enter the host name or IP

AnyDesk

1. Download and install:https://anydesk.com/
2. Provide an ID or set a permanent password after activation
3. Supports Windows, macOS, Linux, Android, iOS

Chrome Remote Desktop

1. Install extensions:Chrome Remote Desktop
2. Set authorization and device name
3. Sign in to your Google account from another device to connect

Linux using VNC

1. Install VNC Server: e.g.sudo apt install tigervnc-standalone-server
2. Set passwords and services
3. Connect using the VNC Viewer tool

Things to note

• Make sure the remote device is powered on and connected to the network
• Firewall rules and NAT forwarding are required (such as RDP using port 3389)
• Protect your account with strong passwords and two-step verification

VPN

What is a VPN?

VPN (Virtual Private Network) is a technology used to establish a protected, encrypted connection over a public network, simulating the functionality of a private network. VPNs provide security and privacy, allowing users to communicate online without being monitored or intercepted.

How VPN works

A VPN hides a user's true IP address by encrypting their Internet traffic and routing it through a protected server. This way, third parties cannot easily track or monitor users’ online activities. When a user connects to a VPN server, its network requests appear to originate from that server's location, effectively hiding the user's true location.

Main uses of VPN

• Privacy protection:Hide user IP addresses to protect personal data from being tracked.
• Secure internet connection:Encrypt data transmission to prevent data from being intercepted on unencrypted networks such as public Wi-Fi.
• Cross-region access:Access geo-restricted websites and content, such as international video streaming platforms.
• Bypass web censorship:Use a VPN to access blocked websites in certain countries or regions where internet is restricted.

Advantages of VPN

• Improve the security and privacy of online activities
• Allow safe use of public Wi-Fi hotspots
• Help users bypass geo-blocking and censorship
• Encrypt data transmission to prevent data leakage

Things to consider when choosing a VPN service

When choosing a VPN service, you should consider the following:

• Security and encryption standards:Make sure your service provider uses strong encryption, such as AES-256.
• Privacy Policy:Confirm whether the service provider has a no-logging policy to prevent user data from being stored or shared.
• Server location:Provide diverse server locations to meet cross-regional access needs.
• Connection speed:Make sure the VPN doesn't significantly slow down your internet speed.

Major VPN Services Comparison

How to choose the right VPN?

When choosing a VPN service, you should consider based on your own needs:

• Speed ​​and stability:For users who need high-speed streaming or gaming, they should choose a VPN with high-speed servers.
• Security and Privacy:If privacy protection is a priority, consider a VPN with a no-logging policy and strong encryption standards.
• Price and Value:Users looking for great value for money can choose services that offer multi-device connectivity and affordable plans.

Conclusion

VPN is an important tool to protect online privacy and security. Especially in the current situation of increasing network security threats, VPN can effectively provide privacy protection and security, and is suitable for users who require high security and an unfettered online experience.

Each VPN service has its own unique pros and cons, and users should choose the most appropriate service based on their needs, budget, and desired features. The choice of VPN not only affects network security and privacy, but also affects the convenience and smoothness of network use.

VPN Rotating IP

What is VPN Rotating IP?

VPN Rotating IP means that when using VPN services, the system will automatically change the user's external IP address regularly. This technology allows users to obtain different IP addresses at certain intervals or with each request when browsing the web or performing online activities.

Purpose of VPN Rotating IP

• Improved privacy: Changing IPs more frequently reduces the likelihood of being tracked.
• Data crawling: When used for web crawling, avoid being blocked due to multiple requests to the same server.
• Unlock content: Bypass IP blocks or regional restrictions and access more of the web.
• Prevent traffic throttling: Prevent the server from limiting the use of a single IP due to too many requests.

advantage

• Improve online anonymity and security
• Overcome Internet Blockades and Restrictions
• Very useful for automation tools and crawlers

shortcoming

• Latency may be slightly higher: Frequent IP switching may result in reduced connection stability.
• Higher cost: Some VPNs offer this feature for an additional fee.
• Configuration and use may be complex.

Applicable occasions

VPN Rotating IP is particularly suitable for situations where a high degree of anonymity is required, such as conducting data analysis, testing network applications in multiple locations, or conducting network activities in more restricted areas.

How to choose a VPN that supports Rotating IP

• Confirm if the provider has automatic IP rotation.
• Compare the frequency of rotation (e.g. per minute, per request).
• Check the geographical coverage and speed of the VPN server.
• Choose a reputable service provider to avoid the risk of data leakage.

network monitoring

Network monitoring refers to the monitoring and management of network traffic, equipment and applications to ensure normal network operation and detect abnormal behavior early. Through network monitoring, companies or individuals can ensure the stability, performance and security of the network.

Test network stability

Network Stability indicator

Evaluating network quality should not only look at download speed. Stability is mainly determined by the following three key indicators:

• Latency/Ping: The time, in milliseconds (ms), required for data to be sent from your device to the server and back. The lower and more stable the number, the better.
• Jitter: The degree of fluctuation of the delay time. If the ping value fluctuates high and low, it means that the network is extremely unstable, which may easily cause online meetings or games to be disconnected.
• Packet Loss: The percentage of data lost during transmission. Ideally this should be 0%, any percentage of packets being lost will cause noticeable lag.

Basic terminal test commands (Ping)

This is the simplest and most direct way to test long-term stability. You can observe network interruptions or delays by sending packets continuously.

Windows (PowerShell or CMD):

ping -t 8.8.8.8

Note: -t means continue testing until you press Ctrl + C to stop.

Ubuntu / macOS (Terminal)：

ping 8.8.8.8

Advanced Network Path Analysis (MTR)

MTR (My Traceroute) combines the functions of Ping and Traceroute. It can simultaneously check the delay and packet loss rate of each node (route) from your computer to the destination, helping to determine which link is the problem.

Install and execute on Ubuntu:

sudo apt update && sudo apt install mtr
mtr 8.8.8.8

Web version of real-time detection tool

If you don't want to use commands, the following web tools provide graphical stability analysis:

• Cloudflare Speed Test: Provides very detailed analysis of latency, jitter, and network performance under "no-load" and "load" conditions.
• Packet Loss Test: Specially designed to detect packet loss and can simulate different application scenarios (such as Zoom video or online games).
• Fast.com: Provided by Netflix, click "Show more information" to view latency and upload speed.

Suggestions for improving network stability

• Switch to a physical network cable: Wi-Fi is easily affected by physical obstacles and other radio spectrum interference. Switching to a wired connection (Ethernet) is the most effective way to improve stability.
• Change DNS server: Sometimes the ISP's DNS is unstable, you can try to manually set it to Google (8.8.8.8) or Cloudflare (1.1.1.1).
• Restart network equipment: The router may experience cache overflow or overheating after long-term operation. Regular restarting will help maintain performance.

Passively monitor network stability

Core principles

Passive Network Monitoring is different from active monitoring (such as Ping) in that it does not actively generate test traffic, but evaluates stability by intercepting and analyzing existing network packets in the system. This approach puts zero load on network bandwidth and reflects the connection quality of real-world applications, such as video streaming or web browsing.

Commonly used passive monitoring techniques

1. TCP Retransmissions Analysis (TCP Retransmissions)

This is the most accurate indicator of network stability. When a packet is lost during transmission, the sender will retransmit the packet. By monitoring the retransmission rate, you can know the true packet loss situation of the network.

• Observation indicators: A retransmission rate above 1% usually indicates line instability or congestion.
• command tool:usenetstat -sView system statistics.

2. Interface Statistics

The operating system kernel records the number of errors for each network interface. This can reveal hardware-level issues, such as a damaged network cable or a faulty network card.

ip -s link show eth0

Check the output forerrors、droppedoroverrunfield. If these values ​​continue to increase, it indicates a stability concern in the physical layer or driver.

Recommended open source monitoring tools

vnStat: lightweight traffic analysis

vnStat reads through/procIt operates with core statistics in the file system and consumes very little CPU.

• use: Record hourly and daily traffic trends.
• Install：sudo apt install vnstat
• advantage: Does not require root permissions and is suitable for long-term background execution.

ntopng: Deep Packet Inspection (DPI)

This is the most powerful graphical passive monitoring tool. It identifies packet types and calculates delays and retransmissions for each connection.

• Function: Shows which devices are using up a lot of bandwidth and flags poor quality connections.
• interface: Provides a web-based dashboard that displays network health in real time.

How to monitor through system logs

When a serious network disconnection occurs or a driver crashes, the Linux system log will record relevant messages:

dmesg | grep -i eth0
journalctl -u NetworkManager

Search keywords such as"Link down"or"Reset adapter", which can help you confirm the exact time and hardware status of the disconnection.

Summary suggestions

For passive monitoring, it is recommended to start withvnStatObserve the abnormal start of traffic; if you find that there is a lag at a specific time point, then usenetstatCheck the TCP retransmission rate, or viewSystem logDetermine whether the hardware connection is interrupted.

Windows network interface stability monitoring

1. Query available network cards and names

In Windows, the name of the network interface (such as "Ethernet 2" or "Wi-Fi") is the same as the name of the network interface in Linux.eth0different. To find out which interfaces are currently available on your system, use the following method:

• PowerShell command:

  Get-NetAdapter

  This will list the names, interface descriptions and current connection status of all network cards.
• CMD command:

  netsh interface ipv4 show interface

  This lists the index value (Idx), status, and name of each interface.

2. Test the network stability of a specific interface

After you confirm the network card name (for example, "Ethernet 2"), you can test its connection quality in the following ways:

• Specify the source IP for Ping:To ensure that the test traffic goes through a specific network card, you need to first find out the IP of the network card and then use-Sparameter:

  # 1. Check IP
  netsh interface ipv4 show addresses "ethernet 2"
  # 2. Specify IP test
  ping 8.8.8.8 -S [yourIP] -t

• Passive statistics monitoring:Determine whether the hardware or driver is stable by checking "dropped packets" or "error packets":

  Get-NetAdapterStatistics -Name "Ethernet 2" | Select-Object Name, *Error*, *Discard*

3. Fixed the problem of missing counters in Performance Monitor (Perfmon)

If you don't see it in Performance MonitorNetwork InterfaceCategory, usually performance counter corruption.

• Common error code 2:when executinglodctr /rWhen error code 2 appears, it means that the system cannot find the backup file. Please try switching toSysWOW64Directory execution:

  cd C:\Windows\SysWOW64
  lodctr /r
  cd C:\Windows\System32
  lodctr /r

• Enable counter:Make sure the counter is not disabled:lodctr /e:PerfOS。

4. Alternative: Use PowerShell for instant monitoring

If the "Performance Monitor" of the graphical interface still cannot be repaired, you can directly use PowerShell to read the underlying data, which does not rely on the UI interface and is more reliable:

• Continuously monitor for receive errors:

  Get-Counter "\Network Interface(*)\Packets Received Errors" -Continuous

• View a summary of all network statistics:This can help you quickly determine whether the instability comes from physical layer errors or system-side packet loss.

  Get-NetAdapterStatistics | Format-Table Name, ReceivedPacketErrors, OutboundPacketErrors, ReceivedDiscardedPackets

suggestion:ifGet-NetAdapterStatisticsThe Error value in continues to rise. Please check the physical network cable or update the network card driver first.

Netreal Integrated System CPS

The core of the CPS (Cyber-Physical Systems) business model is to highly integrate virtual networks (Cyber) with physical sensing and equipment (Physical), and create value beyond traditional manufacturing or services through real-time data feedback and analysis. This model is often closely linked to Industry 4.0, the Internet of Things (IoT) and the Digital Twin.

core value proposition

• Predictive maintenance:Monitor the health status of equipment through sensors and perform repairs before failures occur to reduce downtime losses.
• Highly customized production:The production line can automatically adjust parameters according to cloud orders to achieve small-volume and diverse flexible manufacturing.
• Resource optimization:Instantly optimize the allocation of power, raw materials and manpower to improve overall equipment efficiency (OEE).

Main types of business models

critical success factors

• Data interoperability standards:Solve the integration problem of communication protocols (such as OPC UA, MQTT) between different devices.
• Edge computing capabilities:Process high-frequency data instantly close to the device to reduce cloud latency.
• Information security protection:After physical devices are connected to the Internet, it is crucial to prevent hacker attacks and data leakage.

Source of profit

Under the CPS framework, the profit point shifts from one-time hardware sales to long-term subscription fees, software licensing fees, automatic supply of consumables, and data analysis service fees. This allows businesses to build long-term relationships with customers rather than a single transaction.

Email

definition

• Email is a communication method that sends and receives text, attachments, pictures, videos and other messages through the Internet.
• Users need to send and receive mail via an email address (such as [email protected])
• Is one of the most common digital communication tools in modern times

Basic composition

• Sender (From):The email address from which the message is sent
• Recipient (To):Primary recipient’s email address
• Copy (Cc):Also notify other recipients
• Blind copy (Bcc):Hide recipient list
• Subject:The title of the email
• Content (Body):The content of the email, supports plain text or HTML format
• Attachment:Files can be attached, such as images, documents, and compressed files

Common service providers

• Gmail (provided by Google)
• Outlook/Hotmail (provided by Microsoft)
• Yahoo! Mail
• Apple iCloud Mail
• Exclusive emails provided by major companies or schools

transport protocol

• SMTP：Responsible for sending mail
• POP3：Delete the server copy after downloading the email locally
• IMAP：Emails are saved on the server and can be synchronized across devices

feature

• Cross-platform, cross-border instant delivery
• Support attachments and multimedia
• Can be divided into groups and sent in bulk
• Combined with filtering, labeling, and search functions for easy management

Things to note

• Avoid clicking on links or attachments in emails from unknown sources to prevent phishing attacks and viruses
• Improve account security with two-step verification
• In business situations, you need to pay attention to etiquette and format and maintain professionalism.

Suggestions for using email rules

Categorized inbox

• Automatically categorize based on sender, such as "Boss", "Customer", "Internal Team".
• Classify according to subject keywords, such as "Invoice", "Quotation", "Itinerary Notice".
• Create exclusive folders for different projects and automatically archive related emails.
• Create a dedicated folder for "important customers" and prioritize them.
• Emails of the type "Bill" and "Payment Notification" are automatically classified and saved to facilitate auditing.

Marks and flags

• Automatically add flags or labels to important emails for easy follow-up.
• Set high-priority alerts for emails that require a quick response.

Sort by recipient status

• "Send to me only" emails reinforce reminders and indicate that they need to be dealt with directly.
• When "I am the recipient", it is classified as general to-do and followed up normally.
• When "I am in copy (Cc)", it is marked as secondary and can be postponed.
• Emails "I am not a recipient or copy" are marked as possibly being sent in bulk or not directly related, and may be ignored as appropriate.

Automatic replies and forwarding

• Automatically reply to emails based on specific conditions, such as automatic reply notifications during holidays.
• Automatically forward emails from specific senders or subjects to other colleagues or teams.

Prevent your inbox from filling up

• Automatically move advertising letters and promotional letters to the "Promotion" and "Advertising" folders.
• E-mails determined to be "spam" are automatically moved to the spam folder.
• Set up a schedule to delete certain categories (such as notification letters from a month ago) to save space.

Exclusions and Exceptions

• To prevent important emails from being misclassified, set "skip other rules" for specific important senders.
• Set exceptions for situations with multiple conditions, such as sending an email to the main inbox even if it's from a specific partner.

Maintenance and updates

• Regularly review and adjust email rules to avoid outdated or repeated settings.
• Review folder classifications every six months to ensure compliance with current workflows.

Send Email in Bash

Common tools

• mail / mailx: Simple email delivery tool
• sendmail: Low-level email sending program, powerful but requires configuration
• ssmtp(outdated),msmtp: Simplify SMTP transfers
• mutt: Powerful text interface email tool that supports attached files

Installation example (Debian/Ubuntu)

sudo apt update
sudo apt install mailutils

Basic usage (mail)

echo "This is the content of the message" | mail -s "Subject" [email protected]

Send attachment

echo "content" | mail -s "subject" -A /path/to/file.txt [email protected]

some versionsmailNot supported-A, can be used insteadmutt：

echo "content" | mutt -s "subject" -a /path/to/file.txt -- [email protected]

Use msmtp + mail (supports Gmail, SMTP)

1. Install:

sudo apt install msmtp msmtp-mta mailutils

2. Edit profile~/.msmtprc：

defaults
auth           on
tls            on
tls_trust_file /etc/ssl/certs/ca-certificates.crt
logfile        ~/.msmtp.log

account        gmail
host           smtp.gmail.com
port           587
from           [email protected]
user           [email protected]
password       your_app_password

account default : gmail

3. Permission settings:

chmod 600 ~/.msmtprc

4. Send email:

echo "content" | mail -s "subject" [email protected]

Check email sending history

If usingmsmtp, can be viewed~/.msmtp.log。

Things to note

• If you use services such as Gmail, you need to enable App Password
• Make sure the mail server is not blocking SMTP connections
• If you need to send a large number of emails, please consider using the email API (such as SendGrid)

Gmail

1. Gmail’s email capacity

• Single email size limit:Maximum 25 MB (including attachments).
• Attachment larger than 25 MB:If the attachment exceeds this size, it will be automatically uploaded to Google Drive and a download link will be included in the email.
• Total storage space:Shared storage with a Google Account (free account defaults to 15 GB, upgradeable to higher).

2. Supported attachment formats

Gmail supports most common file formats, but will block potentially risky files (such as `.exe` or compressed files containing executable files).

• Allowed formats:Documents (PDF, Word, Excel), pictures (JPG, PNG, GIF), compressed files (ZIP, RAR), etc.
• Blocked formats:Executable files (such as `.exe`), compressed files that may contain viruses.

3. Email search function

Gmail provides powerful search capabilities to quickly find specific messages:

• Basic search:Enter keywords (such as subject, sender, or recipient).
• Advanced search operators:
  • from:Search for a specific sender, e.g.from:[email protected]
  • to:Search for messages sent to specific recipients.
  • subject:Search for a specific topic.
  • has:attachmentSearch for messages with attachments.

4. Email automation function

• Tag management:You can use labels to categorize emails and set rules to automatically apply labels.
• Filter:Automate actions (such as move to folder, tag, or delete) based on criteria (such as sender or subject).
• Automatic reply:Enable Vacation Reply to automatically respond to incoming messages when you're away.

5. Security features

• Spam filtering:Gmail automatically moves suspicious messages to your spam folder.
• Two-step verification:2FA (two-factor authentication) can be enabled for increased account security.
• Encrypted transmission:Emails are encrypted using TLS (Transport Layer Security) to protect email content.

6. Cross-device use

• Web version:Full functionality available in any browser.
• Mobile App:The official Gmail app is available for iOS and Android, supporting real-time notifications and multi-account management.
• Third-party email clients:Supports using IMAP or POP3 settings, such as managing Gmail emails in Outlook and Apple Mail.

7. Troubleshooting

• Unable to send email:Check whether the attachment size exceeds the limit or is blocked by the network firewall.
• Email not received:Check your spam folder or make sure the sender is entered correctly.
• Login issues:Confirm that the account password is correct and check that two-step verification is enabled.

Gmail adds copy recipients when replying to messages

Operation steps

1. Open the email you want to reply to.
2. Click the "Reply" button to enter the reply screen.
3. In the reply window, the recipient's name or email address will be displayed.
4. Click the recipient's name or address, the "Cc" and "Bcc" buttons will appear on the right side.
5. ClickCc, the "Cc" field will be displayed below.
6. Enter the person you want to send a copy to in the "Cc" field.
7. After completing the email content, click "Send".

Additional information

• In order to keep the interface simple, Gmail hides the Cc/Bcc button by default and will only display it when the recipient is clicked.
• "Cc" (copy) means that the recipient will see the message and others will see that he is one of the recipients.
• If you want to hide copy recipients, use "Bcc" (blind copy).

Gmail mail rules

1. Functions of Gmail email rules

Gmail's mail rules feature (filters) can automatically perform actions on messages that meet criteria, such as classifying, labeling, deleting, or forwarding. This helps manage large amounts of email and improves efficiency.

2. How to create email rules

1. Open Gmail, click the gear icon in the upper right corner, and select "View all settings."
2. switch toFilters and blocked addressesPagination.
3. ClickCreate new filter。
4. Enter filter conditions in the pop-up window, for example:
   • sender:Filter messages from specific senders.
   • theme:Filter messages containing specific keywords.
   • Includes accessories:Filter messages containing attachments.
5. Click "Create Filter" and select the action to perform, for example:
   • Move to a folder.
   • Add tags.
   • Delete or mark as read.
6. ClickCreate filterFinish.

3. Application examples of Gmail rules

• Categorize important emails:Automatically label emails from supervisors or clients as "Important."
• Remove advertising emails:Emails targeting specific keywords (such as "promotion") are automatically moved to the spam folder.
• Centrally manage attachment emails:Move messages containing attachments to the Attachments folder.

4. Modify or delete existing rules

1. Go into Gmail settings and switch toFilters and blocked addressesPagination.
2. Find the rule you want to modify or delete.
3. Click Edit to make changes, or Delete to remove the rule.

5. Precautions

• Rule conditions will be executed in sequential order. If multiple rules conflict, the execution order may need to be adjusted.
• Gmail's rules only apply to newly received emails, and existing emails need to be applied manually.
• Too many rules may affect execution efficiency. It is recommended to review and optimize the rules regularly.

6. Advanced functions: combine labels and rules

You can use Gmail's labels feature to manage your emails more efficiently:

• When creating a filter, specific tags are automatically added.
• Use label colors to quickly identify email types.
• Set up Gmail to automatically hide messages with specific labels from your main inbox.

Summarize

Gmail's email rules are powerful and flexible, helping you automate email management, save time and improve efficiency. Create and optimize rules based on your needs to keep your inbox organized.

Thunderbird email rules usage

In Thunderbird, you can automatically manage and organize email by setting up mail rules (filters). The following steps explain how to create and manage email rules.

1. Open Thunderbird and go to your inbox.
2. In the menu above, clicktool > Message filter。
3. In the dialog box that opens, select the account for which you want to create the rule.

1. In the message filter dialog box, clickNewbutton.
2. In the pop-up window, give the rule a name, such as "Mobile Subscription."
3. In the "Meets the following" section, select the criteria, for example:
   • Condition options:sender、themeorrecipient。
   • Specify conditions, such asIncludeorNot included。
   • Enter a keyword, such as "newsletter".

In the "Perform the following actions" section, specify the actions Thunderbird should perform on messages that match the criteria, for example:

• Move messages to a specific folder
• Mark as read
• Delete message
• Apply label

1. After confirming that the settings are correct, clickSureSave rules.
2. Return to the Message Filter dialog box and make sure the new rule is checked to enable it.
3. When finished, close the message filter dialog box.

To manually apply a rule to an existing message:

1. Opentool > Message filter。
2. After selecting the rule, clickExecute in folder, the filter will be applied automatically.

In this way, you have successfully set up Thunderbird email rules to manage your inbox content more effectively.

Automated email sorting

The core of managing multiple POP3 and Webmail accounts is reducing time switching between windows and using filters for automatic categorization. Here are three main ways to do this:

Centralized management: with Gmail at the core

This is the most recommended way to funnel all external email into one powerful search engine.

• POP3 account import:Add a POP3 account in "Accounts & Import" in Gmail settings. Gmail automatically crawls messages on a regular basis.
• Webmail automatic forwarding:Set "automatic forwarding" of Webmail such as Outlook and Yahoo to Gmail to obtain more immediate mail receiving speed than POP3.
• Automatic labeling rules:Set filters to automatically label messages from different originating accounts (e.g. business, personal, forum) and archive non-urgent messages directly, skipping your inbox.

Unified window management: using an email client

If you don't want all your mail to be stored on Google servers, you can use software that supports Unified Inbox.

Automated filtering logic settings

No matter which tool you use, it’s recommended to build the following automation logic to keep your inbox clean:

• Blacklist and whitelist:Automatically categorize emails containing the words unsubscribe or unsubscribe to the "Subscription content" label.
• Automatic cleaning after expiration:Set rules to automatically mark notification emails older than 30 days as read or move them to the trash.
• Keyword priority:Automatically star and notify emails with subject lines such as "urgent", "invoice" or "quote".

It is recommended to start by integrating one of the most commonly used POP3 accounts into Gmail, observe whether the crawling frequency meets your needs, and then gradually expand to other accounts.

Browser

definition

• Browser (web browser) is software used to access and browse Internet resources
• Users can access the website through the website (URL) and display text, images, videos and interactive content
• In addition to basic browsing functions, modern browsers also support extensions, security mechanisms and cross-platform synchronization.

Common browsers

• Google Chrome
• Mozilla Firefox
• Microsoft Edge
• Apple Safari
• Opera

core technology

• Rendering engine:Parse and display HTML, CSS (example: Blink, WebKit, Gecko)
• JavaScript engine:Execute interactive programs on the web page (example: V8, SpiderMonkey)
• Network protocol:Supports HTTP, HTTPS, FTP, etc.

Main functions

• Open and browse multiple tabs
• Bookmark management and browsing history
• Password storage and automatic form filling
• Extensions and plug-ins
• Cross-device synchronization (after account login)

Security features

• Privacy mode (incognito mode)
• Block pop-ups and trackers
• HTTPS encrypted connection
• Malicious website and download file warnings

future development

• Faster rendering and loading speeds
• AI assistant and smart search integration
• Stricter privacy and security protection
• AR/VR web technical support

Chrome Settings Home Page

Show home button

1. Open Chrome and click on the upper right corner⋮ Menu > Settings
2. Select on the leftAppearance
3. Find the "Show Home Button" and turn on the switch
4. Choose below:
   • New pagination page: Clicking the home page icon will open a blank page
   • Custom URL: Enter the homepage URL you want, such ashttps://www.google.com

Automatically load homepage when opening Chrome

1. In settings, click on the leftOn startup
2. choose:
   • Open a specific page or group of pages
3. Click "Add New Page" and enter the homepage URL you want

Additional information

• The homepage icon is the small house pattern on the left side of the address bar. It will only appear if it is manually enabled.
• The "On startup" setting allows Chrome to automatically open the specified page every time it is started.

Tor Browser

What is Tor Browser?

Tor Browser is a web browser designed to protect user privacy and anonymity. It uses the Tor network to encrypt the user's network traffic through multiple layers and disperse it to nodes around the world to hide the user's real IP address and Internet activities.

How Tor Browser works

Tor Browser uses so-called "onion routing" technology to encrypt data in layers and pass them through several relay nodes in sequence. These nodes cannot completely track or identify the source of the data, making users' browsing behavior more difficult to monitor or track.

Advantages of Tor Browser

• Privacy Protection: Effectively hide the user’s IP address to avoid tracking of online behavior.
• Anonymity: Through multi-layer encryption, the anonymity of online activities is guaranteed.
• Cross-region access: bypass network blocks and access restricted websites and content.

Tor browser usage scenarios

Tor Browser is suitable for users who require high privacy and security, such as journalists, activists, researchers, etc. In addition, Tor is also used to access restricted content, helping users overcome regional restrictions.

Tor Browser Limitations

• Slower speeds: Because traffic passes through multiple nodes, network speeds may be slower than average browsers.
• Some website restrictions: Some websites block access to the Tor network or restrict certain functions.

Tor Browser Translation Plugin

Privacy risk warning

Installing translation plugins in Tor Browser creates serious security issues. The main reasons include:

• Fingerprint tracking:Each additional plug-in makes your browser unique and allows websites to easily identify you.
• Real IP leaks:Requests from some translation plug-ins may not go through the Tor network, but directly connect to the translation server, causing your original IP to be exposed.
• Data analysis:When using services like Google Translate or Bing, the content of the pages you view is transmitted to these tech giants, destroying anonymity.

Alternative: Privacy-preserving translation tools

In order to balance translation requirements and anonymity, it is recommended to use the following methods that do not require the installation of plug-ins:

1. Lingva Translate

Lingva is an open source Google Translate frontend that removes all trackers and proxies your requests on the backend. You can open the web version directly in Tor Browser.

2. SimplyTranslate

This is a Lingva-like project that supports Google and DeepL translation engines. It also provides a privacy-friendly web interface and does not require the installation of any extensions.

If you still need to install the plug-in, please follow the steps

If you decide to install despite understanding the risks, here are the steps for core Firefox add-ons:

1. Install Simple Translate

This is a plug-in based on Google Translate but relatively lightweight and highly open source. You can search for and install it from the Firefox Add-ons store.

2. Enable incognito mode access

Since Tor Browser runs in permanent private browsing mode by default, you must configure it on the plugin management page:

1. Click "Kits and Themes" in the menu.
2. Find Simple Translate.
3. Check "Run in private window" as "Allow".

Plug-in feature comparison table

Official recommendations

Tor project officials strongly recommend "not to install any additional plug-ins." The safest approach is to open a separate tab and manually copy the text to the translated web page, rather than letting the plug-in automatically detect the web page content.

Tor Browser specified country

How it works

By default, Tor Browser randomly selects nodes around the world to establish loops. To specify a specific export country (Exit Node), you must modify the Tor configuration filetorrc. This forces your traffic out of servers in a specific country, making websites think you are located in that country.

Modification steps

1. Find the torrc configuration file

The location of the configuration file depends on your operating system:

• Windows: Tor Browser\Browser\TorBrowser\Data\Tor\torrc
• macOS: ~/Library/Application Support/TorBrowser-Data/Tor/torrc
• Linux: [Installation directory]/browser/TorBrowser/Data/Tor/torrc

2. Edit file content

Open using a text editortorrc, and add the following directive at the end of the file:

ExitNodes {US}
StrictNodes 1

in{US}is the ISO code of the country (braces cannot be omitted). Common codes include: United States{US},Japan{JP},Germany{DE},U.K{GB}。

3. Restart the browser

After saving the file, completely close and restart Tor Browser to take effect.

Parameter description

Anonymous risk warning

Specifying the country manually will significantly reduce your anonymity:

• Path Predictability:Narrowing the selection of nodes makes it easier for traffic analysis attacks to track your identity.
• Fingerprint characteristics:Your behavior is different from other Tor users using the default settings, which creates unique browsing characteristics.
• Availability:Some countries have a smaller number of nodes, which may result in slower connections or frequent disconnections.

Authentication settings

After completing the setup, you can visitcheck.torproject.orgOr any IP lookup website to confirm that the location shown is for the country you specified.

Lynx web browser

Lynx is a long-established and powerfultext-based web browser, developed in 1992 at the University of Kansas. Its main features areCompletely independent of graphical interface (GUI), which can only render the plain text content of the web page.

Main features and functions

1. Plain text and keyboard navigation

• No graphic display:Lynx cannot render images, videos, Flash, JavaScript, CSS styles, or any complex graphic elements. For images it will start with[IMAGE]or[INLINE]etc. tags are replaced and images can be displayedaltProperty literal.
• Keyboard operation:All browsing and operations are done via the keyboard. Users primarily navigate using the arrow keys, the Enter key, and specific hotkeys.

2. Performance and speed

• Since there is no need to render graphics, Lynx starts up and loads web pages very quickly, especially on slow network connections.

3. Accessibility

• Lynx is ideal for visually impaired users. Because it only displays pure text content, it can perfectly cooperate with screen readers and text-to-speech software to provide a good web browsing experience.

4. Agreement support

• Supports various Internet protocols such as HTTP, HTTPS, FTP and Gopher.
• While it cannot execute JavaScript, it can handle basic HTML forms and cookies.

Application scenarios

Although modern browsers are feature-rich, Lynx still plays an important role in specific situations:

• Server management:Lynx is a useful tool for inspecting web pages and downloading files on remote servers without a graphical interface (such as via SSH connection).
• Low bandwidth environment:In areas where Internet access is limited or expensive, using Lynx can significantly save bandwidth and time.
• Web development and testing:Web designers and developers can use Lynx to test web contentstructure and semanticsis good and the content is still accessible without the aid of CSS and JavaScript (i.e. testing accessibility).
• Browse anonymously:Lynx offers somewhat less tracking risk than graphical browsers by not loading graphics and other tracking scripts.

Basic operating instructions (part)

Lynx outputs content directly

As a text mode browser, Lynx's most common and powerful usage isExecute directly in the command line and output the content of the web page to the standard output (stdout), for scripting, content retrieval, or quick web page inspection. This makes Lynx an excellent non-interactive web content extraction tool.

Lynx basic non-interactive command format

To have Lynx output content directly rather than entering an interactive browsing interface, you typically need to use-dumpor-printparameter.

1. Use-dumpParameters (most commonly used)

-dumpThe parameter will render the contents of the specified URL into plain text format and output it directly to standard output (screen or pipe). It is the most commonly used mode for extracting web content.

lynx -dump [options] url > [output file name]

Command example: Retrieve web content

The following command will fetch the content of the Google homepage and output the results to the terminal:

lynx -dump https://www.google.com/

The following command will save the contents to a file calledgoogle.txt's archives:

lynx -dump https://www.google.com/ > google.txt

Common command line options (Options)

in use-dumpmode, you can use other options to control the output format and behavior:

Command example: Output only the link list

This is useful for extracting all URLs from a web page:

lynx -dump -listonly https://www.example.com/

Command example: Processing pages that require authentication

lynx -dump -auth=user:password https://secure.example.com/

2. Use-sourceParameters (output raw HTML)

If your goal is to obtain a web page that has not been formatted by LynxOriginal HTML source code, you should use-sourceparameters, this is similar to usingcurlorwget。

lynx -source https://www.example.com/

This mode outputs raw, unrendered HTML text, suitable for further use.grep、sedorawkWait for tools to process.

Site: Target multiple sites in Google search

Basic rules

Google'ssite:instructionOnly one website can be specified at a time, cannot write multiple sites directly.

Wrong writing (invalid):

site:youtube.com site:vimeo.com "Teaching"

Correct way: Use OR to match multiple sites

To search multiple sites, you can combine them using the OR operator:

(site:youtube.com OR site:vimeo.com) "Teaching"

This will allow you to search both YouTube and Vimeo sites for "tutorial" content.

example

• (site:youtube.com OR site:bilibili.tv) "Python Course"
• (site:github.com OR site:gitlab.com) "login system"

Things to note

• ORMust be capitalized.
• Use parentheses to separate multiplesite:Wrapping can avoid semantic errors.
• Search results will still be sorted according to Google's algorithm, and site results will not be distributed evenly.

in conclusion

Google site:Only one website can be specified at a time.To search multiple sites please use OR operation and add parentheses。

Cloud

definition

• Cloud is a technology that provides computing, storage, data processing and application services through the Internet
• Users can access it anytime and anywhere without relying on a single physical device.
• Widely used in enterprises, education, entertainment and personal life

Main service model

• IaaS (Infrastructure as a Service):Provide virtual servers, storage and network resources, such as AWS EC2, Google Compute Engine
• PaaS (Platform as a Service):Provide application development and deployment environments, such as Google App Engine, Microsoft Azure App Service
• SaaS (Software as a Service):Software is provided on a subscription basis and can be used without installation, such as Google Workspace, Microsoft 365

Common applications

• Cloud storage:Google Drive、Dropbox、iCloud
• cloud computing:AWS、Microsoft Azure、Google Cloud Platform
• Cloud collaboration:Google Docs、Slack、Notion
• Video and games:Netflix、YouTube、Xbox Cloud Gaming

advantage

• Access data anytime, anywhere
• Reduce hardware costs and maintenance burden
• Flexible expansion, adjust resources according to needs
• Supports multi-person collaboration and real-time synchronization

shortcoming

• Relies on network connection, limited when offline
• There may be information security and privacy risks
• Long-term subscription costs may be higher than self-built systems

future trends

• More AI and big data analysis services combined
• Edge Computing improves real-time processing capabilities
• Strengthening cloud security and encryption technology
• Cross-platform and multi-cloud integration

Google Drive

Google Drive is a cloud storage and file management service launched by Google. Users can use this platform to store files, synchronize data to multiple devices, and collaborate with others in real time. It is not only a file storage space, but also deeply integrated with Google office software.

Core functions

• File storage and backup:Provides cloud space to store pictures, videos, documents, compressed files and other formats to prevent data from being lost due to hardware damage.
• Sync across devices:Supports web version, mobile device (iOS/Android) and desktop application to ensure that users can read the latest version on different devices.
• Powerful search function:Integrating Google search technology, you can search file content by keywords, and even use optical character recognition (OCR) technology to identify text in images or PDFs.
• Instant collaboration:Deep integration with Google Docs, spreadsheets, and presentations allows multiple people to edit the same file at the same time, and provides a complete revision history.

Storage and planning

Google Drive storage space is shared by Google accounts (including Gmail, Google Photos):

Security and privacy protection

Google Drive adopts a multi-layered security mechanism to protect user data:

• Transmission and storage encryption:Files are encrypted when transmitted to the cloud and stored in the data center.
• Malware scan:The system will automatically scan uploaded files to detect and block known viruses or malware.
• Fine access control:Users can customize the sharing permissions of files, such as setting them to "view only", "suggesting" or "editable", and can cancel the sharing link at any time.
• Two-step verification (2FA):Prevent unauthorized access through enhanced account login mechanisms.

Third-party application integration

In addition to Google's native software, Google Drive also supports hundreds of third-party applications, such as drawing tools, PDF editors, mind mapping software, etc. Users can open and process these specially formatted files directly in the cloud drive interface.

Google Drive for PC and sync

Google Drive for Desktop is an integrated application that replaces the old Backup & Sync. It allows users to access cloud files directly from the computer's File Explorer (Windows) or Finder (macOS), and provides two different synchronization logics to process data.

Two modes of file synchronization

When setting up Google Drive for PC, users must choose one of the following sync methods for their Google Drive folders:

Computer folder backup function

In addition to the cloud drive synchronization mentioned above, the program also allows users to select specific folders on the computer (such as desktop, files, pictures) for backup:

• Sync to Google Drive: Upload the local folder to the "Computer" tab of the cloud drive, and any changes made on either side will be synchronized.
• Back up to Google Photos: If the folder contains photos or videos, you can choose to back up only to Photos and take advantage of Google Photos' sorting feature.

Operating principles and technical features

Google Drive for PC ensures data consistency through the following mechanisms:

• Virtual disk drive:After installation, a virtual machine codenamed G: (or other letters) will appear on the system, allowing the cloud space to operate like an external hard drive.
• Differential synchronization:When the file content changes, the system only uploads or downloads the changed part (Block-level delta sync) to improve transmission efficiency.
• Conflict handling:If multiple devices edit the same file at the same time, Google will generate a copy and mark it as "conflict" to avoid data overwriting.
• Instant notification:When file synchronization is completed or an error occurs, a real-time status notification will pop up in the system taskbar.

Setup and management suggestions

In order to optimize the user experience, it is recommended to make the following adjustments:

• Bandwidth limitations:If you are worried that synchronization will occupy too much network resources, you can limit the upload and download rates in the settings.
• Offline access:In "Streaming Mode", right-click on frequently used files and select "Offline Access" to ensure that they can still be edited when the network is disconnected.
• Temporary storage path:Make sure the scratch disk has enough space, otherwise errors may occur when editing large files such as videos.

Google Web App

Google Messages for the web

Introduction

Google Messages for Web lets you send and receive SMS, Color Messaging (MMS), and Rich Communications Services (RCS) messages from your computer.

How to get started

1. On your Android phone, open the Google Messages app.
2. Click the "More options" icon in the upper right corner and select "Device pairing."
3. In your computer's browser, go toGoogle Messages for the web。
4. Use the Google Messages app on your phone to scan the QR code on the webpage to complete the pairing.

Once you complete the above steps, you can view and send messages on your computer.

Things to note

• When sending text messages from a computer, the connection between your computer and your phone is used, so you may need to pay fees from your telecommunications provider.
• Make sure both your phone and computer are connected to a stable Internet connection for the best experience.

FAQ

If you encounter problems during connection or use, please refer toFix issues with messaging or Google Messages connections, for detailed troubleshooting instructions.

Video conferencing system

What is a video conferencing system?

Video conferencing systemIt is a system that supports remote video communication, connecting participants in different locations through the Internet, allowing them to communicate face to face. The system usually includes cameras, microphones, monitors and video conferencing software, and is used in scenarios such as corporate meetings, distance education and team collaboration.

Functions of video conferencing system

• High-resolution video transmission:Supports high-definition and even 4K video transmission to ensure clear and stable video in meetings.
• Multi-party connection:It can accommodate multiple participants to join the meeting at the same time and supports connections from all over the world.
• Content sharing:Allows users to share files, presentations, and screens during meetings to improve collaboration efficiency.
• Video recording function:Provide meeting recordings for subsequent reference or for make-up sessions for absentees.
• Interactive tools:Including instant chat, electronic whiteboard and voting functions to enhance meeting interactivity.

Application scope of video conferencing system

Video conferencing systems are widely used in corporate internal and cross-border meetings, online education, medical consultation, customer service and government meetings, etc., and are particularly suitable for situations that are widely distributed and require instant communication.

Advantages and challenges of video conferencing systems

The advantage of video conferencing systems lies in their convenience and cost-effectiveness, allowing enterprises to reduce travel costs and improve collaboration efficiency. However, it has high requirements for network stability, and privacy and security issues need to be considered, such as video encryption and access control. In addition, participants’ hardware and network equipment may also affect the meeting experience.

Rack server

Rack server

Rack serverIt is a server designed to be installed in a standard server rack and is suitable for centralized management in data centers and enterprise server rooms. It has a flat appearance and takes up little space. Multiple servers can be stacked together to improve space utilization efficiency.

Advantages of Rack Servers

• High-density installation:Multiple rack servers can be installed on a standard 19-inch rack, saving space and making management easier.
• Easy to extend:As demand grows, the number of servers can easily be added to expand processing power.
• Centralized management:Make server management more efficient with centralized cabling and management tools.
• Good thermal design:Rack-mounted servers are usually equipped with powerful cooling systems and are suitable for long-term operation.

Common rack server specifications

Rack servers use "U" (unit) as the height unit, and one U is equal to 1.75 inches. Common specifications include 1U, 2U, and 4U, with larger numbers indicating thicker servers and more internal space, usually suitable for different processors and expansion needs.

Application scenarios of rack servers

Rack-mounted servers are widely used in enterprise data centers, website hosting, cloud computing, database management and other fields, and are suitable for environments that require high-density computing and stable performance.

Factors to consider when choosing a rack server

• Processor performance:Choosing a multi-core processor can increase computing speed and is suitable for multi-tasking.
• Memory capacity:Based on application requirements, select sufficient memory to support stable server operation.
• Storage solution:The combination of SSD and HDD can provide a balance of speed and capacity to adapt to different data storage needs.
• Thermal and power management:Good cooling system and power efficiency design can reduce the risk of failure during server operation.

set-top box

1. What is a set-top box?

Set-Top Box (STB) is a device connected to a TV that converts digital signals into images and audio, allowing users to watch content from different sources through the TV, such as digital TV, Internet streaming and other multimedia services.

2. Functions of set-top box

• Digital TV reception:Receives and decodes digital TV signals to provide high-definition or standard-definition TV programs.
• Internet streaming:Supports streaming platforms such as Netflix, YouTube, Disney+, etc., allowing users to watch videos on demand.
• Multimedia playback:Local audio and video files can be played via USB or external hard drive.
• App supports:Some set-top boxes have built-in application stores that allow downloading of a variety of applications, such as music, games, etc.

3. Types of set-top boxes

• Digital TV top box:Designed for receiving and decoding digital TV signals.
• Network set-top box:Equipped with network connection capabilities for video streaming and web browsing.
• Hybrid set-top box:Combining digital TV and Internet streaming functions to provide more diverse services.

4. Advantages of using set-top boxes

• Improve the selectivity of TV programs and provide more content sources.
• Supports HD or 4K resolution to improve viewing quality.
• Real-time update and upgrade functions ensure continuous updates of software and content.

5. How to choose a suitable set-top box?

When purchasing a set-top box, you can consider the following factors:

• Purpose requirements:Need digital TV, or would you prefer a streaming service?
• Resolution support:Choose a set-top box that supports Full HD or 4K depending on your TV specifications.
• Systems and Applications:Prefer Android or other platform-specific apps?
• Budget:Choose products that fit your budget based on features and brands.

P2P

definition

• P2P (Peer-to-Peer, peer-to-peer) is a network architecture
• Different from the traditional "client-server" model, each node (Peer) in P2P has both "client" and "server" roles
• Resources and information can be shared directly between nodes without relying on a single central server.

Application examples

• File sharing:BitTorrent、eMule
• IM:Skype (early versions used P2P architecture)
• Blockchain and Cryptocurrency:Bitcoin, Ethereum, etc. are all based on P2P networks
• Video streaming:Some live streaming and video platforms use P2P to reduce server load

feature

• Decentralized architecture, no single point of failure
• Resource sharing is highly efficient and suitable for large-scale transmission
• The more nodes there are, the better the network performance is usually
• Security and privacy require special attention because data is circulated directly between users.

advantage

• Reduce server costs and pressure
• Strong fault tolerance, some nodes can still operate offline
• Good scalability and can grow with the addition of nodes

shortcoming

• Data transfer speed may be limited by the network quality of the node
• Lack of centralized management may lead to security risks
• Often abused for illegal downloading or pirated resource sharing

information security

Information Security refers to protecting information and its key elements (such as systems, hardware, and networks) from unauthorized access, use, disclosure, destruction, modification, or review. Its core concept is based on the "Three Elements of CIA" and aims to ensure the integrity and availability of data.

CIA Triad

These three basic principles are the basis for designing any security strategy:

• Confidentiality: Ensure that only authorized personnel or systems can access sensitive information to prevent data leakage.
• Integrity: Ensure that data will not be modified or damaged without authorization during transmission or storage, and maintain the accuracy of the data.
• Availability: Ensuring that authorized users can have stable and timely access to information systems or services when needed.

Common security threats

In today's network environment, information security faces diverse threats and challenges:

• Malware: including viruses, worms, Trojans and ransomware, used to damage systems or extort property.
• Social Engineering: Taking advantage of human weaknesses to conduct fraud, such as phishing emails, to obtain account passwords.
• Denial of service attack (DoS/DDoS): paralyzing a target server through a large amount of invalid traffic, disrupting its availability.
• Man-in-the-middle attack (MITM): An attacker intercepts and alters data between two ends of the communication, destroying confidentiality and integrity.

Information Security Defense Mechanism

To combat the above threats, organizations typically adopt a multi-layered defense strategy:

Recommendations for personal information security protection

Strengthening personal information security awareness is the first line of defense for data protection:

• Regular updates: Keep the operating system and all applications up to date to patch security vulnerabilities.
• Strong passwords and MFA: Have complex, unique passwords for different accounts and enable two-step verification when possible.
• Handle links with caution: Do not click on links and attachments in text messages or emails from unknown sources.
• Back up your data: Follow the 3-2-1 backup rule (at least three backups, using two different media, one stored offsite).

Introduction to encryption and decryption

Device fingerprint

Device fingerprinting is a technology that uniquely identifies a user's device by collecting specific information about the browser, hardware, software and network settings. Unlike traditional cookies, device fingerprints do not require any data to be stored on the client, making them more invisible and difficult to remove.

Device fingerprint components

Device fingerprints are a combination of multiple seemingly mundane parameters. When these parameters are superimposed, they produce extremely high uniqueness. Common collection metrics include:

• Browser properties: browser type, version, user agent (User-Agent), preferred language, time zone.
• Screen and display: Screen resolution, color depth, system font list (via Canvas rendering or CSS detection).
• Hardware information: number of CPU cores, memory size, graphics card model (tested through WebGL rendering).
• Network characteristics: IP address, private IP leaked by WebRTC, network latency characteristics.
• System settings: operating system version, installed plug-ins (Plugins), whether to enable Do Not Track (Do Not Track).

Commonly used detection techniques

Canvas Fingerprinting

This is one of the most common techniques. The website will ask the browser to draw a hidden graphic or text in the background. Due to slight differences in the processing of pixel rendering by different operating systems, drivers and graphics cards, the hash value (Hash) of the image data generated will become a unique identification tag.

AudioContext Fingerprinting

Similar to Canvas drawing, this technology uses the Web Audio API to process audio signals. Different devices process audio frequencies in slightly different ways, which can be used to generate acoustic fingerprints.

Application scenarios

Countermeasures

Since device fingerprints use normal system parameters, it is very difficult to completely prevent them. However, you can reduce the chance of being identified through the following methods:

• Use a private browser: such as Tor Browser or Brave, which normalizes parameters or adds random noise to make the characteristics look the same for all users.
• Disabling JavaScript: Although it will prevent most fingerprinting, it will cause most website functions to fail (text-only access can be achieved using the Lynx browser).
• Use a VPN or Proxy: Hide your real IP address and change time zone information.
• Anti-fingerprint plug-ins: Browser extensions such as CanvasBlocker are used to forge rendering results.

metadata track

Metadata Trail refers to the "data about data" automatically generated by the system during digital activities. Although metadata does not contain the specific content of communications, by collecting and analyzing these digital footprints, third parties can accurately piece together a user's behavioral patterns, social connections, and geographic location.

Common metadata types

Digital files and online activities leave different levels of metadata, which together constitute a complete behavioral trajectory:

• Communication metadata:Who to call, duration of call, duration of call, email path header, SMS delivery time.
• File metadata:The creator of the file, the date it was modified, the version of the editing software used, and even the GPS longitude and latitude (such as the EXIF ​​information of the photo).
• Network metadata:IP address, browser fingerprint, visited URL, jump source page, DNS query record.
• Device metadata:Device serial number, battery status, remaining storage space, currently connected Wi-Fi node.

The threat of metadata to information security

Even if communication content is encrypted, metadata traces can still cause serious privacy leaks:

• Behavioral analysis:By analyzing the time and frequency of web browsing, the user's daily routine or religious preferences can be inferred.
• Social map:Even without looking at the content of the conversation, a complete social network can be established just from "who contacted whom at what time".
• Identity deanonymization:Through cross-platform metadata comparison (such as the same device fingerprint appearing in different accounts), anonymous activities can be linked to real identities.

Manage and clean metadata tracks

In order to reduce the risks caused by digital traces, the following technical means can be used to clean or cover up:

Application of metadata in forensics and law

In digital forensics, metadata traces are an indispensable source of evidence. Forensics personnel can track the attacker's intrusion path and operation timeline by examining file system logs (MFT), network traffic records, and system temporary archives. This is why in highly confidential environments, in addition to content encryption, traffic obfuscation (Obfuscation) is emphasized to protect metadata. It is recommended that you make a habit of checking and removing sensitive metadata before sharing any digital assets.

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