ethX

ethX is a generic placeholder name used in Linux systems to denote Ethernet network interfaces, where X represents a numeric index assigned by the kernel (e.g., eth0, eth1). This naming convention emerged during the early development of Linux networking as a simple way to identify physical Ethernet controllers in the order they were detected during boot.

Traditionally, the Linux kernel assigned interface names sequentially based on driver initialization order and PCI bus enumeration. The first Ethernet device discovered became eth0, the second eth1, and so forth. System administrators configured these interfaces through distribution-specific network scripts, typically located in /etc/network/interfaces or /etc/sysconfig/network-scripts/. The ifconfig and ip commands allowed runtime management of ethX devices, enabling configuration of IP addresses, subnet masks, and other parameters.

In 2012, the introduction of systemd and its Predictable Network Interface Names scheme fundamentally altered this approach. Modern Linux distributions now assign names based on firmware topology, physical location, or MAC address, producing identifiers like enp0s3 or eno1. This change eliminated race conditions where interface numbering could vary between reboots. However, ethX persists in documentation, tutorials, and as a fallback when predictable naming fails. Many virtualization platforms and container systems continue using ethX for virtual interfaces due to its simplicity. Administrators can revert to traditional naming by disabling the predictable scheme through kernel boot parameters or udev rules.