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Diffstat (limited to 'udev-config/doc/55-lfs.txt')
| -rw-r--r-- | udev-config/doc/55-lfs.txt | 92 |
1 files changed, 9 insertions, 83 deletions
diff --git a/udev-config/doc/55-lfs.txt b/udev-config/doc/55-lfs.txt index 7b09c79a0..5f116f9b7 100644 --- a/udev-config/doc/55-lfs.txt +++ b/udev-config/doc/55-lfs.txt @@ -1,94 +1,20 @@ Purpose of rules file: -This is the core rules file for Udev on LFS. If these rules were not included, -most devices would either only work for root, or would not work at all. - +Most of the rules installed by Udev itself create devices with the correct +properties. This file contains rules that have not been merged upstream yet. Description of rules: -By default, Udev creates device nodes with UID 0, GID 0, and permissions 0660, -and in one flat directory structure with all nodes in /dev. This does not -always work well. - -KERNEL=="ptmx" - -Any uevent generated by the kernel with a name matching "ptmx" will match this -rule. Note that the matching done by Udev is shell-style; these are not regex -matches. For the ptmx device, we first change the permisions, by assigning to -the MODE value: - -KERNEL=="ptmx", MODE="0666" - -We also assign a different GID to /dev/ptmx (also all other TTY devices), by -assigning to the GROUP value: - -KERNEL=="ptmx", MODE="0666", "GROUP="tty" - - -There are also devices that should not be in /dev, because historically they -have been created in subdirectories instead. For instance, all Alsa devices -have traditionally been put into the /dev/snd subdirectory: - -KERNEL=="controlC[0-9]*", <...>, NAME="snd/%k" - -"%k" expands into "the original value of KERNEL" (note: not the pattern that was -matched against). This type of rule puts any matching device into the snd/ -subdirectory. - -Sometimes we need to move devices based on more than just their name. For -example, USB printer devices need to be moved to /dev/usb/lpX, but we can't -match only "lp[0-9]*", because that would also match parallel port printers. -So we match both KERNEL and SUBSYSTEMS in this case, to move USB printers only. - - -Some devices also commonly have symlinks pointing to them -- for example, -/dev/mouse is usually a symlink to /dev/input/mice. We acheive this by -assigning to the SYMLINK value. But note that SYMLINK can store multiple values -(because each device node could have multiple symlinks pointing to it), so we -need to add to the list of symlinks, not overwrite the whole list: - -KERNEL=="mice", <...>, SYMLINK+="mouse" - -If we needed to add multiple symlinks, they would be space-separated inside the -double quotes. - -Of course, symlinks, permissions, and device names can all be combined in a -rule if needed. But note that if you combine permissions and symlinks, or if -you combine GROUP and symlinks, the permissions of the symlink will not be -modified, only those of the target device. (This is because the kernel does -not pay any attention to the permissions on symlinks, only the permissions on -their targets, and there's no reason to change something that won't be used.) - - -Finally, we have this rule: - -SUBSYSTEM=="usb_device", PROGRAM="/bin/sh -c 'X=%k; X=$${X#usbdev}; B=$${X%%%%.*} D=$${X#*.}; echo bus/usb/$$B/$$D'", NAME="%c" - -This rule matches any device under the SUBSYSTEM of usb_device. (All devices -that were traditionally created under /proc/bus/usb/ use this subsystem.) We -tell Udev to run the specified PROGRAM; Udev will save the output of this -program (it will be available under %c later). - -The program itself is a shell that starts by setting the variable X to the -original kernel name (which is "usbdevB.D" for these devices, where B and D are -the bus and device numbers of the USB device). Then, the rule re-sets X to the -value of X with the string "usbdev" removed from the start. So now, X has the -value "B.D". Then, the rule sets B to the value of X after a period, and all -characters following it, have been removed from the end; this sets B to just -the string "B" (just the bus number of the USB device). Then, the rule sets D -to the value of X after a period, and all characters before it, have been -removed from the beginning; this sets D to just the string "D" (just the device -number). +By default, Udev creates device nodes with UID 0, GID 0, and permissions 0660. -Then, the rule echoes "bus/usb/$B/$D" (bus/usb/bus-number/device-number), so -Udev will capture that value. The rule sets NAME="%c" to put the device node -at /dev/bus/usb/bus-number/device-number. (This is the same layout that the -/proc/bus/usb/ devices used.) +ISDN-related devices should be owned by the 'dialout' group, hence the following +rule (and similar): -Most of the doubled characters in this rule are doubled so that Udev does not -interpret them. The rule looks all the more confusing because of this method -of escaping special characters. +KERNEL=="ippp[0-9]*", GROUP="dialout" +The RTC-related rules cause the setclock bootscript to be run as soon as the +RTC device has been created by Udev, meaning that times in log files, for +example, are as accurate as possible as quickly as possible. A final word of caution: Any particular rule must be written on one line, and a comma must separate each part of the rule. |