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/hot-
plug, and normally holds the value /sbin/hotplug. Except for special-
ized configurations such as initrd(4) configurations, that identifies a
shell script which delegates to specific "policy agents", /etc/hot-
plug/NAME.agent. The name of the agent is given by the kernel as the
first command-line parameter. The name corresponds to a specific ker-
nel subsystem whose events it processes (e.g. "usb", "pci", "net"
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 dis-
connected 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 http://linux-hotplug.sourceforge.net/ web site.
hotplug is developed by Linux Hotplugging Project http://linux-hot-
This manual page was originally written by Fumitoshi UKAI
<email@example.com>, for the Debian GNU/Linux system (but may be used
by others), based on original Japanese version of manpage.
February 2001 HOTPLUG(8)