611 lines
20 KiB
Groff
611 lines
20 KiB
Groff
'\" t
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.\" Title: udev
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.\" Author: Greg Kroah-Hartmann <greg@kroah.com>
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.\" Generator: DocBook XSL Stylesheets v1.78.0 <http://docbook.sf.net/>
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.\" Date: 05/30/2015
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.\" Manual: udev
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.\" Source: udev
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.\" Language: English
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.\"
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.TH "UDEV" "7" "" "udev" "udev"
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.\" -----------------------------------------------------------------
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.\" * Define some portability stuff
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.\" -----------------------------------------------------------------
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.\" ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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.\" http://bugs.debian.org/507673
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.\" http://lists.gnu.org/archive/html/groff/2009-02/msg00013.html
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.\" ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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.ie \n(.g .ds Aq \(aq
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.el .ds Aq '
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.\" -----------------------------------------------------------------
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.\" * set default formatting
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.\" -----------------------------------------------------------------
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.\" disable hyphenation
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.nh
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.\" disable justification (adjust text to left margin only)
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.ad l
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.\" -----------------------------------------------------------------
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.\" * MAIN CONTENT STARTS HERE *
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.\" -----------------------------------------------------------------
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.SH "NAME"
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udev \- Dynamic device management
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.SH "DESCRIPTION"
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.PP
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udev supplies the system software with device events, manages permissions of device nodes and may create additional symlinks in the
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/dev
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directory, or renames network interfaces\&. The kernel usually just assigns unpredictable device names based on the order of discovery\&. Meaningful symlinks or network device names provide a way to reliably identify devices based on their properties or current configuration\&.
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.PP
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The udev daemon,
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\fBudevd\fR(8), receives device uevents directly from the kernel whenever a device is added or removed from the system, or it changes its state\&. When udev receives a device event, it matches its configured set of rules against various device attributes to identify the device\&. Rules that match may provide additional device information to be stored in the udev database or to be used to create meaningful symlink names\&.
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.PP
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All device information udev processes is stored in the udev database and sent out to possible event subscribers\&. Access to all stored data and the event sources is provided by the library libudev\&.
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.SH "RULES FILES"
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.PP
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The udev rules are read from the files located in the system rules directory
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/lib/udev/rules\&.d, the volatile runtime directory
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/run/udev/rules\&.d
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and the local administration directory
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/etc/udev/rules\&.d\&. All rules files are collectively sorted and processed in lexical order, regardless of the directories in which they live\&. However, files with identical filenames replace each other\&. Files in
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/etc
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have the highest priority, files in
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/run
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take precedence over files with the same name in
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/lib\&. This can be used to override a system\-supplied rules file with a local file if needed; a symlink in
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/etc
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with the same name as a rules file in
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/lib, pointing to
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/dev/null, disables the rules file entirely\&. Rule files must have the extension
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\&.rules; other extensions are ignored\&.
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.PP
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Every line in the rules file contains at least one key\-value pair\&. Except for empty lines or lines beginning with
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#, which are ignored\&. There are two kinds of keys: match and assignment\&. If all match keys match against their values, the rule gets applied and the assignment keys get the specified values assigned\&.
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.PP
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A matching rule may rename a network interface, add symlinks pointing to the device node, or run a specified program as part of the event handling\&.
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.PP
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A rule consists of a comma\-separated list of one or more key\-value pairs\&. Each key has a distinct operation, depending on the used operator\&. Valid operators are:
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.PP
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==
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.RS 4
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Compare for equality\&.
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.RE
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.PP
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!=
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.RS 4
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Compare for inequality\&.
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.RE
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.PP
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=
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.RS 4
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Assign a value to a key\&. Keys that represent a list are reset and only this single value is assigned\&.
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.RE
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.PP
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+=
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.RS 4
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Add the value to a key that holds a list of entries\&.
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.RE
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.PP
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\-=
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.RS 4
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Remove the value from a key that holds a list of entries\&.
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.RE
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.PP
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:=
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.RS 4
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Assign a value to a key finally; disallow any later changes\&.
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.RE
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.PP
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The following key names can be used to match against device properties\&. Some of the keys also match against properties of the parent devices in sysfs, not only the device that has generated the event\&. If multiple keys that match a parent device are specified in a single rule, all these keys must match at one and the same parent device\&.
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.PP
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\fIACTION\fR
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.RS 4
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Match the name of the event action\&.
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.RE
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.PP
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\fIDEVPATH\fR
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.RS 4
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Match the devpath of the event device\&.
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.RE
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.PP
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\fIKERNEL\fR
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.RS 4
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Match the name of the event device\&.
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.RE
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.PP
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\fINAME\fR
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.RS 4
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Match the name of a network interface\&. It can be used once the NAME key has been set in one of the preceding rules\&.
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.RE
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.PP
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\fISYMLINK\fR
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.RS 4
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Match the name of a symlink targeting the node\&. It can be used once a SYMLINK key has been set in one of the preceding rules\&. There may be multiple symlinks; only one needs to match\&.
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.RE
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.PP
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\fISUBSYSTEM\fR
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.RS 4
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Match the subsystem of the event device\&.
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.RE
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.PP
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\fIDRIVER\fR
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.RS 4
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Match the driver name of the event device\&. Only set this key for devices which are bound to a driver at the time the event is generated\&.
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.RE
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.PP
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\fIATTR{\fR\fI\fIfilename\fR\fR\fI}\fR, \fISYSCTL{\fR\fI\fIkernel parameter\fR\fR\fI}\fR
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.RS 4
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Match sysfs attribute values of the event device\&. Trailing whitespace in the attribute values is ignored unless the specified match value itself contains trailing whitespace\&.
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Match a kernel parameter value\&.
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.RE
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.PP
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\fIKERNELS\fR
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.RS 4
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Search the devpath upwards for a matching device name\&.
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.RE
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.PP
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\fISUBSYSTEMS\fR
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.RS 4
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Search the devpath upwards for a matching device subsystem name\&.
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.RE
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.PP
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\fIDRIVERS\fR
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.RS 4
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Search the devpath upwards for a matching device driver name\&.
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.RE
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.PP
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\fIATTRS{\fR\fI\fIfilename\fR\fR\fI}\fR
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.RS 4
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Search the devpath upwards for a device with matching sysfs attribute values\&. If multiple
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\fIATTRS\fR
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matches are specified, all of them must match on the same device\&. Trailing whitespace in the attribute values is ignored unless the specified match value itself contains trailing whitespace\&.
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.RE
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.PP
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\fITAGS\fR
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.RS 4
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Search the devpath upwards for a device with matching tag\&.
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.RE
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.PP
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\fIENV{\fR\fI\fIkey\fR\fR\fI}\fR
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.RS 4
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Match against a device property value\&.
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.RE
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.PP
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\fITAG\fR
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.RS 4
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Match against a device tag\&.
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.RE
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.PP
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\fITEST{\fR\fI\fIoctal mode mask\fR\fR\fI}\fR
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.RS 4
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Test the existence of a file\&. An octal mode mask can be specified if needed\&.
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.RE
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.PP
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\fIPROGRAM\fR
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.RS 4
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Execute a program to determine whether there is a match; the key is true if the program returns successfully\&. The device properties are made available to the executed program in the environment\&. The program\*(Aqs standard output is available in the
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\fIRESULT\fR
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key\&.
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.sp
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This can only be used for very short\-running foreground tasks\&. For details, see
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\fIRUN\fR\&.
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.RE
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.PP
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\fIRESULT\fR
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.RS 4
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Match the returned string of the last
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\fIPROGRAM\fR
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call\&. This key can be used in the same or in any later rule after a
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\fIPROGRAM\fR
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call\&.
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.RE
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.PP
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Most of the fields support shell glob pattern matching and alternate patterns\&. The following special characters are supported:
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.PP
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*
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.RS 4
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Matches zero or more characters\&.
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.RE
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.PP
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?
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.RS 4
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Matches any single character\&.
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.RE
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.PP
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[]
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.RS 4
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Matches any single character specified within the brackets\&. For example, the pattern string
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tty[SR]
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would match either
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ttyS
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or
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ttyR\&. Ranges are also supported via the
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\-
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character\&. For example, to match on the range of all digits, the pattern
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[0\-9]
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could be used\&. If the first character following the
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[
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is a
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!, any characters not enclosed are matched\&.
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.RE
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.PP
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.RS 4
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Separates alternative patterns\&. For example, the pattern string
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abc|x*
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would match either
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abc
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or
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x*\&.
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.RE
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.PP
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The following keys can get values assigned:
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.PP
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\fINAME\fR
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.RS 4
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The name to use for a network interface\&. The name of a device node cannot be changed by udev, only additional symlinks can be created\&.
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.RE
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.PP
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\fISYMLINK\fR
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.RS 4
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The name of a symlink targeting the node\&. Every matching rule adds this value to the list of symlinks to be created\&.
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.sp
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The set of characters to name a symlink is limited\&. Allowed characters are
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0\-9A\-Za\-z#+\-\&.:=@_/, valid UTF\-8 character sequences, and
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\ex00
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hex encoding\&. All other characters are replaced by a
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_
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character\&.
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.sp
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Multiple symlinks may be specified by separating the names by the space character\&. In case multiple devices claim the same name, the link always points to the device with the highest link_priority\&. If the current device goes away, the links are re\-evaluated and the device with the next highest link_priority becomes the owner of the link\&. If no link_priority is specified, the order of the devices (and which one of them owns the link) is undefined\&.
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.sp
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Symlink names must never conflict with the kernel\*(Aqs default device node names, as that would result in unpredictable behavior\&.
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.RE
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.PP
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\fIOWNER\fR, \fIGROUP\fR, \fIMODE\fR
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.RS 4
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The permissions for the device node\&. Every specified value overrides the compiled\-in default value\&.
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.RE
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.PP
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\fISECLABEL{\fR\fI\fImodule\fR\fR\fI}\fR
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.RS 4
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Applies the specified Linux Security Module label to the device node\&.
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.RE
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.PP
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\fIATTR{\fR\fI\fIkey\fR\fR\fI}\fR
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.RS 4
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The value that should be written to a sysfs attribute of the event device\&.
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.RE
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.PP
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\fISYSCTL{\fR\fI\fIkernel parameter\fR\fR\fI}\fR
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.RS 4
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The value that should be written to kernel parameter\&.
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.RE
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.PP
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\fIENV{\fR\fI\fIkey\fR\fR\fI}\fR
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.RS 4
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Set a device property value\&. Property names with a leading
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\&.
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are neither stored in the database nor exported to events or external tools (run by, for example, the
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\fIPROGRAM\fR
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match key)\&.
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.RE
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.PP
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\fITAG\fR
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.RS 4
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Attach a tag to a device\&. This is used to filter events for users of libudev\*(Aqs monitor functionality, or to enumerate a group of tagged devices\&. The implementation can only work efficiently if only a few tags are attached to a device\&. It is only meant to be used in contexts with specific device filter requirements, and not as a general\-purpose flag\&. Excessive use might result in inefficient event handling\&.
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.RE
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.PP
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\fIRUN{\fR\fI\fItype\fR\fR\fI}\fR
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.RS 4
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Add a program to the list of programs to be executed after processing all the rules for a specific event, depending on
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type:
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.PP
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program
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.RS 4
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Execute an external program specified as the assigned value\&. If no absolute path is given, the program is expected to live in
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/lib/udev, otherwise, the absolute path must be specified\&.
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.sp
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This is the default if no
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\fItype\fR
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is specified\&.
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.RE
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.PP
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builtin
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.RS 4
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As
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\fIprogram\fR, but use one of the built\-in programs rather than an external one\&.
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.RE
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.sp
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The program name and following arguments are separated by spaces\&. Single quotes can be used to specify arguments with spaces\&.
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.sp
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This can only be used for very short\-running foreground tasks\&. Running an event process for a long period of time may block all further events for this or a dependent device\&.
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.sp
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Starting daemons or other long\-running processes is not appropriate for udev; the forked processes, detached or not, will be unconditionally killed after the event handling has finished\&.
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.RE
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.PP
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\fILABEL\fR
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.RS 4
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A named label to which a
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\fIGOTO\fR
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may jump\&.
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.RE
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.PP
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\fIGOTO\fR
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.RS 4
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Jumps to the next
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\fILABEL\fR
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with a matching name\&.
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.RE
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.PP
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\fIIMPORT{\fR\fI\fItype\fR\fR\fI}\fR
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.RS 4
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Import a set of variables as device properties, depending on
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type:
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.PP
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program
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.RS 4
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Execute an external program specified as the assigned value and import its output, which must be in environment key format\&. Path specification, command/argument separation, and quoting work like in
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\fIRUN\fR\&.
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.RE
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.PP
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builtin
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.RS 4
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Similar to
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program, but use one of the built\-in programs rather than an external one\&.
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.RE
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.PP
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file
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.RS 4
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Import a text file specified as the assigned value, the content of which must be in environment key format\&.
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.RE
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.PP
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db
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.RS 4
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Import a single property specified as the assigned value from the current device database\&. This works only if the database is already populated by an earlier event\&.
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.RE
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.PP
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cmdline
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.RS 4
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Import a single property from the kernel command line\&. For simple flags the value of the property is set to
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1\&.
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.RE
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.PP
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parent
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.RS 4
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Import the stored keys from the parent device by reading the database entry of the parent device\&. The value assigned to
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\fBIMPORT{parent}\fR
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is used as a filter of key names to import (with the same shell glob pattern matching used for comparisons)\&.
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.RE
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.sp
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This can only be used for very short\-running foreground tasks\&. For details see
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\fBRUN\fR\&.
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.RE
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.PP
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\fIWAIT_FOR\fR
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.RS 4
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Wait for a file to become available or until a timeout of 10 seconds expires\&. The path is relative to the sysfs device; if no path is specified, this waits for an attribute to appear\&.
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.RE
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.PP
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\fIOPTIONS\fR
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.RS 4
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Rule and device options:
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.PP
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\fBlink_priority=\fR\fB\fIvalue\fR\fR
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.RS 4
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Specify the priority of the created symlinks\&. Devices with higher priorities overwrite existing symlinks of other devices\&. The default is 0\&.
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.RE
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.PP
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\fBstring_escape=\fR\fB\fInone|replace\fR\fR
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.RS 4
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Usually control and other possibly unsafe characters are replaced in strings used for device naming\&. The mode of replacement can be specified with this option\&.
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.RE
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.PP
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\fBstatic_node=\fR
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.RS 4
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Apply the permissions specified in this rule to the static device node with the specified name\&. Static device node creation can be requested by kernel modules\&. These nodes might not have a corresponding kernel device at the time udevd is started; they can trigger automatic kernel module loading\&.
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.RE
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.PP
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\fBwatch\fR
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.RS 4
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Watch the device node with inotify; when the node is closed after being opened for writing, a change uevent is synthesized\&.
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.RE
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.PP
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\fBnowatch\fR
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.RS 4
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Disable the watching of a device node with inotify\&.
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.RE
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.RE
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.PP
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The
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\fINAME\fR,
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\fISYMLINK\fR,
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\fIPROGRAM\fR,
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\fIOWNER\fR,
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\fIGROUP\fR,
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\fIMODE\fR, and
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\fIRUN\fR
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fields support simple string substitutions\&. The
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\fIRUN\fR
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substitutions are performed after all rules have been processed, right before the program is executed, allowing for the use of device properties set by earlier matching rules\&. For all other fields, substitutions are performed while the individual rule is being processed\&. The available substitutions are:
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.PP
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\fB$kernel\fR, \fB%k\fR
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.RS 4
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The kernel name for this device\&.
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.RE
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.PP
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\fB$number\fR, \fB%n\fR
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.RS 4
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The kernel number for this device\&. For example,
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sda3
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has kernel number
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3\&.
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.RE
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.PP
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\fB$devpath\fR, \fB%p\fR
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.RS 4
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The devpath of the device\&.
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.RE
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.PP
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\fB$id\fR, \fB%b\fR
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.RS 4
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The name of the device matched while searching the devpath upwards for
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\fBSUBSYSTEMS\fR,
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\fBKERNELS\fR,
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\fBDRIVERS\fR, and
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\fBATTRS\fR\&.
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.RE
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.PP
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\fB$driver\fR
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.RS 4
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The driver name of the device matched while searching the devpath upwards for
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\fBSUBSYSTEMS\fR,
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\fBKERNELS\fR,
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\fBDRIVERS\fR, and
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\fBATTRS\fR\&.
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.RE
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.PP
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\fB$attr{\fR\fB\fIfile\fR\fR\fB}\fR, \fB%s{\fR\fB\fIfile\fR\fR\fB}\fR
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.RS 4
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The value of a sysfs attribute found at the device where all keys of the rule have matched\&. If the matching device does not have such an attribute, and a previous
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\fBKERNELS\fR,
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\fBSUBSYSTEMS\fR,
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\fBDRIVERS\fR, or
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\fBATTRS\fR
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test selected a parent device, then the attribute from that parent device is used\&.
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.sp
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If the attribute is a symlink, the last element of the symlink target is returned as the value\&.
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.RE
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.PP
|
|
\fB$env{\fR\fB\fIkey\fR\fR\fB}\fR, \fB%E{\fR\fB\fIkey\fR\fR\fB}\fR
|
|
.RS 4
|
|
A device property value\&.
|
|
.RE
|
|
.PP
|
|
\fB$major\fR, \fB%M\fR
|
|
.RS 4
|
|
The kernel major number for the device\&.
|
|
.RE
|
|
.PP
|
|
\fB$minor\fR, \fB%m\fR
|
|
.RS 4
|
|
The kernel minor number for the device\&.
|
|
.RE
|
|
.PP
|
|
\fB$result\fR, \fB%c\fR
|
|
.RS 4
|
|
The string returned by the external program requested with
|
|
\fIPROGRAM\fR\&. A single part of the string, separated by a space character, may be selected by specifying the part number as an attribute:
|
|
%c{N}\&. If the number is followed by the
|
|
+
|
|
character, this part plus all remaining parts of the result string are substituted:
|
|
%c{N+}\&.
|
|
.RE
|
|
.PP
|
|
\fB$parent\fR, \fB%P\fR
|
|
.RS 4
|
|
The node name of the parent device\&.
|
|
.RE
|
|
.PP
|
|
\fB$name\fR
|
|
.RS 4
|
|
The current name of the device\&. If not changed by a rule, it is the name of the kernel device\&.
|
|
.RE
|
|
.PP
|
|
\fB$links\fR
|
|
.RS 4
|
|
A space\-separated list of the current symlinks\&. The value is only set during a remove event or if an earlier rule assigned a value\&.
|
|
.RE
|
|
.PP
|
|
\fB$root\fR, \fB%r\fR
|
|
.RS 4
|
|
The udev_root value\&.
|
|
.RE
|
|
.PP
|
|
\fB$sys\fR, \fB%S\fR
|
|
.RS 4
|
|
The sysfs mount point\&.
|
|
.RE
|
|
.PP
|
|
\fB$devnode\fR, \fB%N\fR
|
|
.RS 4
|
|
The name of the device node\&.
|
|
.RE
|
|
.PP
|
|
\fB%%\fR
|
|
.RS 4
|
|
The
|
|
%
|
|
character itself\&.
|
|
.RE
|
|
.PP
|
|
\fB$$\fR
|
|
.RS 4
|
|
The
|
|
$
|
|
character itself\&.
|
|
.RE
|
|
.SH "HARDWARE DATABASE FILES"
|
|
.PP
|
|
The hwdb files are read from the files located in the system hwdb directory
|
|
/lib/udev/hwdb\&.d, the volatile runtime directory
|
|
/run/udev/hwdb\&.d
|
|
and the local administration directory
|
|
/etc/udev/hwdb\&.d\&. All hwdb files are collectively sorted and processed in lexical order, regardless of the directories in which they live\&. However, files with identical filenames replace each other\&. Files in
|
|
/etc
|
|
have the highest priority, files in
|
|
/run
|
|
take precedence over files with the same name in
|
|
/lib\&. This can be used to override an hwdb file with a local file if needed; a symlink in
|
|
/etc
|
|
with the same name as a hwdb file in
|
|
/lib, pointing to
|
|
/dev/null, disables the hwdb file entirely\&. hwdb files must have the extension
|
|
\&.hwdb; other extensions are ignored\&.
|
|
.PP
|
|
The hwdb file contains data records consisting of matches and associated key\-value pairs\&. Every record in the hwdb starts with one or more match string, specifying a shell glob to compare the database lookup string against\&. Multiple match lines are specified in additional consecutive lines\&. Every match line is compared indivdually, they are combined by OR\&. Every match line must start at the first character of the line\&.
|
|
.PP
|
|
The match lines are followed by one or more key\-value pair lines, which are recognized by a leading space character\&. The key name and value are separated by
|
|
=\&. An empty line signifies the end of a record\&. Lines beginning with
|
|
#
|
|
are ignored\&.
|
|
.PP
|
|
The content of all hwdb files is read by
|
|
\fBudevadm\fR(8)
|
|
and compiled to a binary database located at
|
|
/etc/udev/hwdb\&.bin\&. During runtime only the binary database is used\&.
|
|
.SH "HARDWARE DATABASE FILES"
|
|
.PP
|
|
The hwdb files are read from the files located in the system hwdb directory
|
|
/usr/lib/udev/hwdb\&.d, the volatile runtime directory
|
|
/run/udev/hwdb\&.d
|
|
and the local administration directory
|
|
/etc/udev/hwdb\&.d\&. All hwdb files are collectively sorted and processed in lexical order, regardless of the directories in which they live\&. However, files with identical filenames replace each other\&. Files in
|
|
/etc
|
|
have the highest priority, files in
|
|
/run
|
|
take precedence over files with the same name in
|
|
/usr/lib\&. This can be used to override a system\-supplied hwdb file with a local file if needed; a symlink in
|
|
/etc
|
|
with the same name as a hwdb file in
|
|
/usr/lib, pointing to
|
|
/dev/null, disables the hwdb file entirely\&. hwdb files must have the extension
|
|
\&.hwdb; other extensions are ignored\&.
|
|
.PP
|
|
The hwdb file contains data records consisting of matches and associated key\-value pairs\&. Every record in the hwdb starts with one or more match string, specifying a shell glob to compare the database lookup string against\&. Multiple match lines are specified in additional consecutive lines\&. Every match line is compared indivdually, they are combined by OR\&. Every match line must start at the first character of the line\&.
|
|
.PP
|
|
The match lines are followed by one or more key\-value pair lines, which are recognized by a leading space character\&. The key name and value are separated by
|
|
=\&. An empty line signifies the end of a record\&. Lines beginning with
|
|
#
|
|
are ignored\&.
|
|
.PP
|
|
The content of all hwdb files is read by
|
|
\fBudevadm\fR(8)
|
|
and compiled to a binary database located at
|
|
/etc/udev/hwdb\&.bin, or alternatively
|
|
/usr/lib/udev/hwdb\&.bin
|
|
if you want ship the compiled database in an immutable image\&. During runtime only the binary database is used\&.
|
|
.SH "SEE ALSO"
|
|
.PP
|
|
|
|
\fBudevd\fR(8),
|
|
\fBudevadm\fR(8)
|