HOTPLUG(G)          Linux Programmer's Manual          HOTPLUG(G)



NAME
       hotplug - Linux hotplugging support scripts

SYNOPSIS
       hotplug [ help | --help | NAME ]

       /etc/init.d/hotplug [start|stop|status|restart]

DESCRIPTION
       hotplug is a program which is used by the kernel to notify
       user mode software when some  significant  (usually  hard-
       ware-related) events take place.  An example is when a USB
       or Cardbus device has just been plugged in.  This is  use-
       ful  for  automatically  loading  and  setting up drivers,
       packaged either as kernel modules or  as  user  mode  pro-
       grams.

       The   hotplug   program   path   name   is  registered  in
       /proc/sys/kernel/hotplug, and  normally  holds  the  value
       /sbin/hotplug.  Except for specialized configurations such
       as  initrd(d)  configurations,  that  identifies  a  shell
       script   which  delegates  to  specific  "policy  agents",
       /etc/hotplug/NAME.agent.  The name of the agent  is  given
       by  the  kernel  as the first command-line parameter.  The
       name corresponds to  a  specific  kernel  subsystem  whose
       events it processes (e.g. "usb", "pci", "net" etc.).

       Information  about an event is usually passed to agents in
       the form of environment variables.  Most agents  accept  a
       "ACTION"  variable  that  describes the type of the event.
       It can be, for example, "add" or "remove" to signify  that
       some  device  has  just  been connected to or disconnected
       from the system respectively.  In  such  requests,  agents
       are also given variables describing at the device (and its
       location) so that they can choose the appropriate  drivers
       to set up.

       hotplug  agents aren't necessarily called only by the ker-
       nel though.  While the OS is initializing, the "cold-plug-
       ging"  case,  the hotplug script in /etc/init.d/hotplug is
       invoked to make sure that all device connected at boot are
       properly  configured,  applying  the same rules as if they
       were connected later.

FILES
       /proc/sys/kernel/hotplug   specifies hotplug program path
       /sbin/hotplug              hotplug program (default path name)
       /etc/hotplug/*             hotplug files
       /etc/hotplug/NAME.agent    hotplug subsystem-specific agents
       /etc/hotplug/NAME*         subsystem-specific files, for agents
       /etc/hotplug/NAME/*        driver setup scripts, invoked by agents
       /etc/init.d/hotplug        hotplug system service script


SEE ALSO
       initrd(d)

       The http://linux-hotplug.sourceforge.net/ web site.

AUTHORS
       hotplug  is  developed  by   Linux   Hotplugging   Project
       http://linux-hotplug.sourceforge.net/

       This  manual page was originally written by Fumitoshi UKAI
       <ukai@debian.or.jp>, for the Debian GNU/Linux system  (but
       may be used by others), based on original Japanese version
       of manpage.



                          February 2001                HOTPLUG(G)