What Is SSH, How Does It Work and What Is It Used For?
Learn how SSH works, why port 22 is common, how host keys and user authentication differ, and how encrypted remote terminal sessions are used.
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Learn connection protocols and server management.
Understand how SSH, FTP, FTPS, SFTP and Telnet work; then use practical guides to connect and solve common problems.
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5 guides
What Is FTP and How Do Active and Passive Modes Work?
Learn how FTP uses control and data connections, why port 21 is common, how active and passive modes differ, and where plain FTP falls short.
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What Is FTPS? How Do Explicit and Implicit FTPS Work?
Learn how FTPS adds TLS to FTP, the difference between explicit and implicit FTPS, common ports 21 and 990, and certificate verification.
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What Is SFTP and How Does File Transfer over SSH Work?
Learn how SFTP performs secure file operations over SSH, why port 22 is common, how authentication works, and why SFTP is not FTP over TLS.
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What Is Telnet, How Does It Work and Why Is It Insecure?
Learn how Telnet provides a remote text terminal, why port 23 is common, how it differs from SSH, and why its unencrypted sessions are risky.
Read guide ›SSH
7 guides
How to Connect to SSH from Android: Step-by-Step Guide
Learn how to connect to an SSH server from Android using the host, port, username, password or private key, and troubleshoot common errors.
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How to Fix SSH Connection Refused and Timed Out Errors
Understand SSH connection refused and connection timed out errors and check the host, port, SSH service, firewall, DNS and network in the right order.
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How to Fix SSH Permission Denied (publickey,password)
Fix SSH Permission denied publickey or password errors by checking the username, credentials, authorized_keys ownership, file permissions and sshd settings.
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SSH Public Key vs Private Key: Authentication Guide
Understand SSH public and private keys, generate a key pair, add the public key to a server, use a passphrase and protect the private key.
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How to Resolve an SSH Host Key Changed Warning Safely
Understand why an SSH host key changes, verify the new fingerprint and safely replace only the affected known_hosts entry.
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Why Does SSH Disconnect? Broken Pipe and Keepalive Guide
Diagnose SSH Broken pipe, connection reset and idle-session disconnects using network checks, ServerAliveInterval and server-side evidence.
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What Is an SSH Tunnel? Local, Remote and Dynamic Port Forwarding
Learn SSH local, remote and dynamic port forwarding, the -L, -R and -D options, safe bind addresses and practical tunnel examples.
Read guide ›File transfer
7 guides
FTP vs FTPS vs SFTP: Differences and Which One to Use
Compare FTP, FTPS and SFTP by encryption, ports, connection model and server requirements to choose the right file transfer protocol.
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How to Fix FTP 530 Login Incorrect and Not Logged In
Fix FTP 530 Login incorrect or Not logged in by checking the server, full username, password, account status and FTP or FTPS security settings.
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FTP Connects but Cannot List Directories: Passive Mode Fix
When FTP connects but cannot list folders, troubleshoot passive mode, data ports, NAT, firewall rules, directory permissions and FTPS settings.
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How to Fix FTPS Certificate and TLS Errors Safely
Troubleshoot FTPS certificate name mismatch, expired or untrusted certificates, incomplete chains and TLS connection errors without bypassing security.
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How to Fix SFTP Permission Denied and Upload Errors
Fix SFTP permission denied during upload, folder creation or rename by checking directory ownership, write access, chroot layout and server limits.
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FTP 550 Error: File Unavailable or Access Denied
Fix FTP 550 Requested action not taken by checking the file path, write permission, account root, quota, file name and server policy.
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FTP 425 and 426 Errors: Data Connection and Transfer Problems
Fix FTP 425 cannot open data connection and 426 transfer aborted by checking passive mode, port ranges, NAT, firewalls and network stability.
Read guide ›Server management
1 guides
What Are CHMOD 644 and 755? File Permissions Guide
Learn what CHMOD 644 and 755 mean, how they apply to files and directories, and why overly broad permissions such as 777 are risky.
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