The term U:Line is derived from some of the original IRCd configuration files to indicate a services server, or a server in which all clients require specific access on the 'host' server, to be able to change things like modes. An example of a 'U:Line' would be:
In the interests of history, we still continue to use the term U:Line (As the <oper> block may be referred to an O:Line, for the same reason).
A U:line, in terms of many modern IRCds (such as InspIRCd and UnrealIRCd) is a configuration item that gives a server more permissions. However, U:lines on InspIRCd work slightly different.
A U:Line on an InspIRCd server does not only give extended permissions to the server, but all clients on it. This is normally reserved for services; however, it is possible to U:line a normal server, which will give all clients on that server permission to override some restrictions. It is recommended that this be avoided in production; allowing access to the oper-only commands that are required to override the restrictions will give more fine-grained control, better auditing, and does not require a dedicated oper server.
The u-line privilege must be set on every server individually so that all servers in the network are in agreement, and when granted upon a server name, grants that server, and all users upon that server, the following privileges:
- Modes can be issued from inside or outside a channel, whether you are opped or not
- Modes which are restricted to servers-only or u-lined servers only may be set or unset
- All oper permissions are bypassed, giving the u-lined server unrestricted access to all server commands