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 vari-
ables. 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 appro-
priate drivers to set up.
hotplug agents aren't necessarily called only by the kernel though. While the OS is ini-
tializing, 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-hotplug.sourceforge.net/
This manual page was originally written by Fumitoshi UKAI <firstname.lastname@example.org>, for the
Debian GNU/Linux system (but may be used by others), based on original Japanese version of
February 2001 HOTPLUG(8)