[d736904] | 1 | '\" t
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[2aa3c1c] | 2 | .TH "UDEV" "7" "" "systemd 200" "udev"
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[d736904] | 3 | .\" -----------------------------------------------------------------
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| 4 | .\" * Define some portability stuff
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| 5 | .\" -----------------------------------------------------------------
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| 6 | .\" ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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| 7 | .\" http://bugs.debian.org/507673
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| 8 | .\" http://lists.gnu.org/archive/html/groff/2009-02/msg00013.html
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| 9 | .\" ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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| 10 | .ie \n(.g .ds Aq \(aq
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| 11 | .el .ds Aq '
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| 12 | .\" -----------------------------------------------------------------
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| 13 | .\" * set default formatting
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| 14 | .\" -----------------------------------------------------------------
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| 15 | .\" disable hyphenation
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| 16 | .nh
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| 17 | .\" disable justification (adjust text to left margin only)
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| 18 | .ad l
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| 19 | .\" -----------------------------------------------------------------
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| 20 | .\" * MAIN CONTENT STARTS HERE *
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| 21 | .\" -----------------------------------------------------------------
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| 22 | .SH "NAME"
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| 23 | udev \- Linux dynamic device management
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| 24 | .SH "DESCRIPTION"
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| 25 | .PP
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| 26 | udev supplies the system software with device events, manages permissions of device nodes and may create additional symlinks in the
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| 27 | /dev
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| 28 | 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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| 29 | .PP
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| 30 | The udev daemon,
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| 31 | \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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| 32 | .PP
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| 33 | 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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| 34 | .SH "RULES FILES"
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| 35 | .PP
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| 36 | The udev rules are read from the files located in the system rules directory
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| 37 | /usr/lib/udev/rules\&.d, the volatile runtime directory
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| 38 | /run/udev/rules\&.d
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| 39 | and the local administration directory
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| 40 | /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 file names replace each other\&. Files in
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| 41 | /etc
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| 42 | have the highest priority, files in
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| 43 | /run
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| 44 | take precedence over files with the same name in
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| 45 | /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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| 46 | /etc
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| 47 | with the same name as a rules file in
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| 48 | /lib, pointing to
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| 49 | /dev/null, disables the rules file entirely\&.
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| 50 | .PP
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| 51 | Rule files must have the extension
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| 52 | \&.rules; other extensions are ignored\&.
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| 53 | .PP
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| 54 | Every line in the rules file contains at least one key\-value pair\&. Except for empty lines or lines beginning with \*(Aq#\*(Aq, 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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| 55 | .PP
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| 56 | 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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| 57 | .PP
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| 58 | 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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| 59 | .PP
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| 60 | ==
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| 61 | .RS 4
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| 62 | Compare for equality\&.
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| 63 | .RE
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| 64 | .PP
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| 65 | !=
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| 66 | .RS 4
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| 67 | Compare for inequality\&.
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| 68 | .RE
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| 69 | .PP
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| 70 | =
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| 71 | .RS 4
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| 72 | Assign a value to a key\&. Keys that represent a list are reset and only this single value is assigned\&.
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| 73 | .RE
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| 74 | .PP
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| 75 | +=
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| 76 | .RS 4
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| 77 | Add the value to a key that holds a list of entries\&.
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| 78 | .RE
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| 79 | .PP
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| 80 | :=
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| 81 | .RS 4
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| 82 | Assign a value to a key finally; disallow any later changes\&.
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| 83 | .RE
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| 84 | .PP
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| 85 | 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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| 86 | .PP
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| 87 | \fBACTION\fR
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| 88 | .RS 4
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| 89 | Match the name of the event action\&.
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| 90 | .RE
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| 91 | .PP
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| 92 | \fBDEVPATH\fR
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| 93 | .RS 4
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| 94 | Match the devpath of the event device\&.
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| 95 | .RE
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| 96 | .PP
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| 97 | \fBKERNEL\fR
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| 98 | .RS 4
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| 99 | Match the name of the event device\&.
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| 100 | .RE
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| 101 | .PP
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| 102 | \fBNAME\fR
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| 103 | .RS 4
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| 104 | 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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| 105 | .RE
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| 106 | .PP
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| 107 | \fBSYMLINK\fR
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| 108 | .RS 4
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| 109 | 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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| 110 | .RE
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| 111 | .PP
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| 112 | \fBSUBSYSTEM\fR
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| 113 | .RS 4
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| 114 | Match the subsystem of the event device\&.
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| 115 | .RE
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| 116 | .PP
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| 117 | \fBDRIVER\fR
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| 118 | .RS 4
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| 119 | 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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| 120 | .RE
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| 121 | .PP
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| 122 | \fBATTR{\fR\fB\fIfilename\fR\fR\fB}\fR
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| 123 | .RS 4
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| 124 | 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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| 125 | .RE
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| 126 | .PP
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| 127 | \fBKERNELS\fR
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| 128 | .RS 4
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| 129 | Search the devpath upwards for a matching device name\&.
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| 130 | .RE
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| 131 | .PP
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| 132 | \fBSUBSYSTEMS\fR
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| 133 | .RS 4
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| 134 | Search the devpath upwards for a matching device subsystem name\&.
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| 135 | .RE
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| 136 | .PP
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| 137 | \fBDRIVERS\fR
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| 138 | .RS 4
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| 139 | Search the devpath upwards for a matching device driver name\&.
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| 140 | .RE
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| 141 | .PP
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| 142 | \fBATTRS{\fR\fB\fIfilename\fR\fR\fB}\fR
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| 143 | .RS 4
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| 144 | Search the devpath upwards for a device with matching sysfs attribute values\&. If multiple
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| 145 | \fBATTRS\fR
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| 146 | 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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| 147 | .RE
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| 148 | .PP
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| 149 | \fBTAGS\fR
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| 150 | .RS 4
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| 151 | Search the devpath upwards for a device with matching tag\&.
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| 152 | .RE
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| 153 | .PP
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| 154 | \fBENV{\fR\fB\fIkey\fR\fR\fB}\fR
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| 155 | .RS 4
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| 156 | Match against a device property value\&.
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| 157 | .RE
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| 158 | .PP
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| 159 | \fBTAG\fR
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| 160 | .RS 4
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| 161 | Match against a device tag\&.
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| 162 | .RE
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| 163 | .PP
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| 164 | \fBTEST{\fR\fB\fIoctal mode mask\fR\fR\fB}\fR
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| 165 | .RS 4
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| 166 | Test the existence of a file\&. An octal mode mask can be specified if needed\&.
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| 167 | .RE
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| 168 | .PP
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| 169 | \fBPROGRAM\fR
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| 170 | .RS 4
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| 171 | 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 stdout is available in the RESULT key\&.
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| 172 | .sp
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| 173 | This can only be used for very short\-running foreground tasks\&. For details see
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| 174 | \fBRUN\fR\&.
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| 175 | .RE
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| 176 | .PP
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| 177 | \fBRESULT\fR
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| 178 | .RS 4
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| 179 | Match the returned string of the last PROGRAM call\&. This key can be used in the same or in any later rule after a PROGRAM call\&.
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| 180 | .RE
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| 181 | .PP
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| 182 | Most of the fields support shell\-style pattern matching\&. The following pattern characters are supported:
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| 183 | .PP
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| 184 | *
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| 185 | .RS 4
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| 186 | Matches zero or more characters\&.
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| 187 | .RE
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| 188 | .PP
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| 189 | ?
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| 190 | .RS 4
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| 191 | Matches any single character\&.
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| 192 | .RE
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| 193 | .PP
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| 194 | []
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| 195 | .RS 4
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| 196 | Matches any single character specified within the brackets\&. For example, the pattern string \*(Aqtty[SR]\*(Aq would match either \*(AqttyS\*(Aq or \*(AqttyR\*(Aq\&. Ranges are also supported via the \*(Aq\-\*(Aq character\&. For example, to match on the range of all digits, the pattern [0\-9] could be used\&. If the first character following the \*(Aq[\*(Aq is a \*(Aq!\*(Aq, any characters not enclosed are matched\&.
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| 197 | .RE
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| 198 | .PP
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| 199 | The following keys can get values assigned:
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| 200 | .PP
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| 201 | \fBNAME\fR
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| 202 | .RS 4
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| 203 | 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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| 204 | .RE
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| 205 | .PP
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| 206 | \fBSYMLINK\fR
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| 207 | .RS 4
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| 208 | 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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| 209 | .sp
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| 210 | The set of characters to name a symlink is limited\&. Allowed characters are [0\-9A\-Za\-z#+\-\&.:=@_/], valid utf8 character sequences, and "\ex00" hex encoding\&. All other characters are replaced by a \*(Aq_\*(Aq character\&.
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| 211 | .sp
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| 212 | 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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| 213 | .sp
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| 214 | Symlink names must never conflict with the kernel\*(Aqs default device node names, as that would result in unpredictable behavior\&.
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| 215 | .RE
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| 216 | .PP
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| 217 | \fBOWNER\fR, \fBGROUP\fR, \fBMODE\fR
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| 218 | .RS 4
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| 219 | The permissions for the device node\&. Every specified value overrides the compiled\-in default value\&.
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| 220 | .RE
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| 221 | .PP
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| 222 | \fBATTR{\fR\fB\fIkey\fR\fR\fB}\fR
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| 223 | .RS 4
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| 224 | The value that should be written to a sysfs attribute of the event device\&.
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| 225 | .RE
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| 226 | .PP
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| 227 | \fBENV{\fR\fB\fIkey\fR\fR\fB}\fR
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| 228 | .RS 4
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| 229 | Set a device property value\&. Property names with a leading \*(Aq\&.\*(Aq are neither stored in the database nor exported to events or external tools (run by, say, the PROGRAM match key)\&.
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| 230 | .RE
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| 231 | .PP
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| 232 | \fBTAG\fR
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| 233 | .RS 4
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| 234 | 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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| 235 | .RE
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| 236 | .PP
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| 237 | \fBRUN{\fR\fB\fItype\fR\fR\fB}\fR
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| 238 | .RS 4
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| 239 | 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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| 240 | type:
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| 241 | .PP
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| 242 | program
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| 243 | .RS 4
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| 244 | Execute an external program specified as the assigned value\&. If no absolute path is given, the program is expected to live in /usr/lib/udev, otherwise the absolute path must be specified\&.
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| 245 | .sp
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| 246 | This is the default if no
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| 247 | \fItype\fR
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| 248 | is specified\&.
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| 249 | .RE
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| 250 | .PP
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| 251 | builtin
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| 252 | .RS 4
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| 253 | As
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| 254 | \fBprogram\fR, but use one of the built\-in programs rather than an external one\&.
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| 255 | .RE
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| 256 | .sp
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| 257 | The program name and following arguments are separated by spaces\&. Single quotes can be used to specify arguments with spaces\&.
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| 258 | .sp
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| 259 | 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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| 260 | .sp
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| 261 | 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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| 262 | .RE
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| 263 | .PP
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| 264 | \fBLABEL\fR
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| 265 | .RS 4
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| 266 | A named label to which a GOTO may jump\&.
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| 267 | .RE
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| 268 | .PP
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| 269 | \fBGOTO\fR
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| 270 | .RS 4
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| 271 | Jumps to the next LABEL with a matching name\&.
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| 272 | .RE
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| 273 | .PP
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| 274 | \fBIMPORT{\fR\fB\fItype\fR\fR\fB}\fR
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| 275 | .RS 4
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| 276 | Import a set of variables as device properties, depending on
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| 277 | type:
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| 278 | .PP
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| 279 | program
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| 280 | .RS 4
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| 281 | 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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| 282 | \fBRUN\fR\&.
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| 283 | .RE
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| 284 | .PP
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| 285 | builtin
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| 286 | .RS 4
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| 287 | As
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| 288 | \fBprogram\fR, but use one of the built\-in programs rather than an external one\&.
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| 289 | .RE
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| 290 | .PP
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| 291 | file
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| 292 | .RS 4
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| 293 | Import a text file specified as the assigned value, the content of which must be in environment key format\&.
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| 294 | .RE
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| 295 | .PP
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| 296 | db
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| 297 | .RS 4
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| 298 | 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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| 299 | .RE
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| 300 | .PP
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| 301 | cmdline
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| 302 | .RS 4
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| 303 | Import a single property from the kernel command line\&. For simple flags the value of the property is set to \*(Aq1\*(Aq\&.
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| 304 | .RE
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| 305 | .PP
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| 306 | parent
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| 307 | .RS 4
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| 308 | 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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| 309 | \fBIMPORT{parent}\fR
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| 310 | is used as a filter of key names to import (with the same shell\-style pattern matching used for comparisons)\&.
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| 311 | .RE
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| 312 | .sp
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| 313 | This can only be used for very short\-running foreground tasks\&. For details see
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| 314 | \fBRUN\fR\&.
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| 315 | .RE
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| 316 | .PP
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| 317 | \fBWAIT_FOR\fR
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| 318 | .RS 4
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| 319 | 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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| 320 | .RE
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| 321 | .PP
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| 322 | \fBOPTIONS\fR
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| 323 | .RS 4
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| 324 | Rule and device options:
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| 325 | .PP
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| 326 | \fBlink_priority=\fR\fB\fIvalue\fR\fR
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| 327 | .RS 4
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| 328 | 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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| 329 | .RE
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| 330 | .PP
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| 331 | \fBevent_timeout=\fR
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| 332 | .RS 4
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| 333 | Number of seconds an event waits for operations to finish before giving up and terminating itself\&.
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| 334 | .RE
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| 335 | .PP
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| 336 | \fBstring_escape=\fR\fB\fInone|replace\fR\fR
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| 337 | .RS 4
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| 338 | 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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| 339 | .RE
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| 340 | .PP
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| 341 | \fBstatic_node=\fR
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| 342 | .RS 4
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| 343 | 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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| 344 | .RE
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| 345 | .PP
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| 346 | \fBwatch\fR
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| 347 | .RS 4
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| 348 | 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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| 349 | .RE
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| 350 | .PP
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| 351 | \fBnowatch\fR
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| 352 | .RS 4
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| 353 | Disable the watching of a device node with inotify\&.
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| 354 | .RE
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| 355 | .RE
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| 356 | .PP
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| 357 | The
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| 358 | \fBNAME\fR,
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| 359 | \fBSYMLINK\fR,
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| 360 | \fBPROGRAM\fR,
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| 361 | \fBOWNER\fR,
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| 362 | \fBGROUP\fR,
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| 363 | \fBMODE\fR
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| 364 | and
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| 365 | \fBRUN\fR
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| 366 | fields support simple string substitutions\&. The
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| 367 | \fBRUN\fR
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| 368 | 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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| 369 | .PP
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| 370 | \fB$kernel\fR, \fB%k\fR
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| 371 | .RS 4
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| 372 | The kernel name for this device\&.
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| 373 | .RE
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| 374 | .PP
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| 375 | \fB$number\fR, \fB%n\fR
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| 376 | .RS 4
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| 377 | The kernel number for this device\&. For example, \*(Aqsda3\*(Aq has kernel number of \*(Aq3\*(Aq
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| 378 | .RE
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| 379 | .PP
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| 380 | \fB$devpath\fR, \fB%p\fR
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| 381 | .RS 4
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| 382 | The devpath of the device\&.
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| 383 | .RE
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| 384 | .PP
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| 385 | \fB$id\fR, \fB%b\fR
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| 386 | .RS 4
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| 387 | The name of the device matched while searching the devpath upwards for
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| 388 | \fBSUBSYSTEMS\fR,
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| 389 | \fBKERNELS\fR,
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| 390 | \fBDRIVERS\fR
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| 391 | and
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| 392 | \fBATTRS\fR\&.
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| 393 | .RE
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| 394 | .PP
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| 395 | \fB$driver\fR
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| 396 | .RS 4
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| 397 | The driver name of the device matched while searching the devpath upwards for
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| 398 | \fBSUBSYSTEMS\fR,
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| 399 | \fBKERNELS\fR,
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| 400 | \fBDRIVERS\fR
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| 401 | and
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| 402 | \fBATTRS\fR\&.
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| 403 | .RE
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| 404 | .PP
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| 405 | \fB$attr{\fR\fB\fIfile\fR\fR\fB}\fR, \fB%s{\fR\fB\fIfile\fR\fR\fB}\fR
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| 406 | .RS 4
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| 407 | 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 KERNELS, SUBSYSTEMS, DRIVERS, or ATTRS test selected a parent device, then the attribute from that parent device is used\&.
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| 408 | .sp
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| 409 | If the attribute is a symlink, the last element of the symlink target is returned as the value\&.
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| 410 | .RE
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| 411 | .PP
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| 412 | \fB$env{\fR\fB\fIkey\fR\fR\fB}\fR, \fB%E{\fR\fB\fIkey\fR\fR\fB}\fR
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| 413 | .RS 4
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| 414 | A device property value\&.
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| 415 | .RE
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| 416 | .PP
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| 417 | \fB$major\fR, \fB%M\fR
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| 418 | .RS 4
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| 419 | The kernel major number for the device\&.
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| 420 | .RE
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| 421 | .PP
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| 422 | \fB$minor\fR, \fB%m\fR
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| 423 | .RS 4
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| 424 | The kernel minor number for the device\&.
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| 425 | .RE
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| 426 | .PP
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| 427 | \fB$result\fR, \fB%c\fR
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| 428 | .RS 4
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| 429 | The string returned by the external program requested with PROGRAM\&. A single part of the string, separated by a space character, may be selected by specifying the part number as an attribute:
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| 430 | \fB%c{N}\fR\&. If the number is followed by the \*(Aq+\*(Aq character, this part plus all remaining parts of the result string are substituted:
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| 431 | \fB%c{N+}\fR
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| 432 | .RE
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| 433 | .PP
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| 434 | \fB$parent\fR, \fB%P\fR
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| 435 | .RS 4
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| 436 | The node name of the parent device\&.
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| 437 | .RE
|
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| 438 | .PP
|
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| 439 | \fB$name\fR
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| 440 | .RS 4
|
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| 441 | The current name of the device\&. If not changed by a rule, it is the name of the kernel device\&.
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| 442 | .RE
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| 443 | .PP
|
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| 444 | \fB$links\fR
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| 445 | .RS 4
|
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| 446 | A space\-separated list of the current symlinks\&. The value is only set during a remove event or if an earlier rule assigned a value\&.
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| 447 | .RE
|
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| 448 | .PP
|
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| 449 | \fB$root\fR, \fB%r\fR
|
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| 450 | .RS 4
|
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| 451 | The udev_root value\&.
|
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| 452 | .RE
|
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| 453 | .PP
|
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| 454 | \fB$sys\fR, \fB%S\fR
|
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| 455 | .RS 4
|
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| 456 | The sysfs mount point\&.
|
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| 457 | .RE
|
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| 458 | .PP
|
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| 459 | \fB$devnode\fR, \fB%N\fR
|
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| 460 | .RS 4
|
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| 461 | The name of the device node\&.
|
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| 462 | .RE
|
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| 463 | .PP
|
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| 464 | %%
|
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| 465 | .RS 4
|
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| 466 | The \*(Aq%\*(Aq character itself\&.
|
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| 467 | .RE
|
---|
| 468 | .PP
|
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| 469 | $$
|
---|
| 470 | .RS 4
|
---|
| 471 | The \*(Aq$\*(Aq character itself\&.
|
---|
| 472 | .RE
|
---|
| 473 | .SH "SEE ALSO"
|
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| 474 | .PP
|
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| 475 | \fBudevd\fR(8),
|
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| 476 | \fBudevadm\fR(8)
|
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