This signal is generated by the kernel when your controlling terminal goes away. Or, in simplier terms, when you close the Xterm, or hang up a modem. Since daemons run in the background and don't have a controlling terminal, they often use SIGHUP to signal that they should reread their configuration files. This can cause issues with some programs that work as both a daemon and an interactive program, such as fetchmail(1).
7 pages link to SIGHUP:
