When troubleshooting a network connection or configuring a firewall, the first question is whether a port is actually reachable. This guide covers three command-line methods for checking open ports in Linux: nmap, netcat, and the Bash /dev/tcp pseudo-device. What Is an Open...

The lsmod command in Linux lists all currently loaded kernel modules. It reads /proc/modules — a virtual file maintained by the kernel — and formats the output into three labeled columns. lsmod takes no options or arguments. How to Use the lsmod Command in Linux...

The ss command in Linux lists open sockets and active network connections. It replaced the deprecated netstat command and is available by default on all current Linux distributions. ss reads directly from kernel socket data structures, making it noticeably faster than netstat on systems with large numbers of...

The rename command in Linux renames multiple files at once using Perl regular expressions. Unlike mv, which handles one file at a time, rename applies a pattern across every matching filename in a single operation. Two versions exist. The Perl version (available as rename, prename, or file-rename) uses full Perl...

The ftp command in Linux connects to a remote FTP server and transfers files. FTP transmits everything in plain text: credentials and file data are both unencrypted. For transfers over untrusted networks, use SFTP or SCP instead. On trusted internal networks or...