rtnetlinkh

Rtnetlinkh is not a standard term in official Linux documentation, and it most often refers to the Linux header file linux/rtnetlink.h (sometimes informally abbreviated as rtnetlink.h or mis-typed as rtnetlinkh). This header declares the user-space API used to interact with the kernel’s rtnetlink subsystem, which is part of the Netlink interface for routing and networking configuration.

Rtnetlink itself is a Netlink family (NETLINK_ROUTE) that provides a channel for user-space processes to query and modify kernel networking state. It covers objects such as network interfaces, addresses, routes, neighbors, and routing policies. Through rtnetlink, tools can list interfaces, assign IP addresses, add or remove routes, and monitor changes in real time.

The rtnetlink.h header defines the constants, structures, and attribute types needed to construct and parse Netlink messages. Key elements include message types (RTM_ prefixed, such as RTM_NEWLINK, RTM_DELLINK, RTM_GETLINK, RTM_NEWADDR, RTM_NEWROUTE) and attribute types (RTA_OIF for the output interface index, RTA_GATEWAY for a next-hop, IFA_ADDRESS and IFA_LOCAL for addresses). It also provides the rtmsg structure skeletons used to describe the primary object being manipulated and the rtattr mechanism for attaching attributes to messages.

Typical usage involves creating a Netlink socket with AF_NETLINK and NETLINK_ROUTE, building an RTM message with associated rtattrs, sending it to the kernel, and parsing responses. This API underpins many network configuration tools and is a cornerstone of Linux networking management.

Note: if you encountered the term rtnetlinkh, it is likely a misnomer for rtnetlink.h. The official header is linux/rtnetlink.h.