HOTPLUG(8)                 Linux Programmer's Manual                HOTPLUG(8)

       hotplug - Linux hotplugging support scripts

       hotplug [ help | --help | NAME ]

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

       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(4) 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 kernel though.
       While the OS is initializing, the "cold-plugging" 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.

       /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


       The web site.

       hotplug is developed by Linux Hotplugging Project http://linux-

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

                                 February 2001                      HOTPLUG(8)