Show Provided by: udev_229-4ubuntu4_amd64  NAMEudevadm - udev management toolSYNOPSISudevadm [--debug] [--version] [--help] udevadm info options udevadm trigger [options] udevadm settle [options] udevadm control command udevadm monitor [options] udevadm test [options] devpath udevadm test-builtin [options] command devpathDESCRIPTIONudevadm expects a command and command specific options. It controls the runtime behavior of systemd-udevd, requests kernel events, manages the event queue, and provides simple debugging mechanisms.OPTIONS--debug Print debug messages to standard error. --version Print version number. -h, --help Print help text. udevadm info [options] [devpath|file] Queries the udev database for device information stored in the udev database. It can also query the properties of a device from its sysfs representation to help creating udev rules that match this device. -q, --query=TYPE Query the database for the specified type of device data. It needs the --path or --name to identify the specified device. Valid TYPEs are: name, symlink, path, property, all. -p, --path=DEVPATH The /sys path of the device to query, e.g. [/sys]/class/block/sda. Note that this option usually is not very useful, since udev can guess the type of the argument, so udevadm --devpath=/class/block/sda is equivalent to udevadm /sys/class/block/sda. -n, --name=FILE The name of the device node or a symlink to query, e.g. [/dev]/sda. Note that this option usually is not very useful, since udev can guess the type of the argument, so udevadm --name=sda is equivalent to udevadm /dev/sda. -r, --root Print absolute paths in name or symlink query. -a, --attribute-walk Print all sysfs properties of the specified device that can be used in udev rules to match the specified device. It prints all devices along the chain, up to the root of sysfs that can be used in udev rules. -x, --export Print output as key/value pairs. Values are enclosed in single quotes. -P, --export-prefix=NAME Add a prefix to the key name of exported values. -d, --device-id-of-file=FILE Print major/minor numbers of the underlying device, where the file lives on. -e, --export-db Export the content of the udev database. -c, --cleanup-db Cleanup the udev database. --version Print version. -h, --help Print help text. In addition, an optional positional argument can be used to specify a device name or a sys path. It must start with /dev or /sys respectively. udevadm trigger [options] [devpath|file...] Request device events from the kernel. Primarily used to replay events at system coldplug time. -v, --verbose Print the list of devices which will be triggered. -n, --dry-run Do not actually trigger the event. -t, --type=TYPE Trigger a specific type of devices. Valid types are: devices, subsystems. The default value is devices. -c, --action=ACTION Type of event to be triggered. The default value is change. -s, --subsystem-match=SUBSYSTEM Trigger events for devices which belong to a matching subsystem. This option can be specified multiple times and supports shell style pattern matching. -S, --subsystem-nomatch=SUBSYSTEM Do not trigger events for devices which belong to a matching subsystem. This option can be specified multiple times and supports shell style pattern matching. -a, --attr-match=ATTRIBUTE=VALUE Trigger events for devices with a matching sysfs attribute. If a value is specified along with the attribute name, the content of the attribute is matched against the given value using shell style pattern matching. If no value is specified, the existence of the sysfs attribute is checked. This option can be specified multiple times. -A, --attr-nomatch=ATTRIBUTE=VALUE Do not trigger events for devices with a matching sysfs attribute. If a value is specified along with the attribute name, the content of the attribute is matched against the given value using shell style pattern matching. If no value is specified, the existence of the sysfs attribute is checked. This option can be specified multiple times. -p, --property-match=PROPERTY=VALUE Trigger events for devices with a matching property value. This option can be specified multiple times and supports shell style pattern matching. -g, --tag-match=PROPERTY Trigger events for devices with a matching tag. This option can be specified multiple times. -y, --sysname-match=PATH Trigger events for devices with a matching sys device path. This option can be specified multiple times and supports shell style pattern matching. --name-match=NAME Trigger events for devices with a matching device path. This option can be specified multiple times. -b, --parent-match=SYSPATH Trigger events for all children of a given device. -h, --help Print help text. In addition, optional positional arguments can be used to specify device names or sys paths. They must start with /dev or /sys respectively. udevadm settle [options] Watches the udev event queue, and exits if all current events are handled. -t, --timeout=SECONDS Maximum number of seconds to wait for the event queue to become empty. The default value is 120 seconds. A value of 0 will check if the queue is empty and always return immediately. -E, --exit-if-exists=FILE Stop waiting if file exists. -h, --help Print help text. udevadm control command Modify the internal state of the running udev daemon. -x, --exit Signal and wait for systemd-udevd to exit. -l, --log-priority=value Set the internal log level of systemd-udevd. Valid values are the numerical syslog priorities or their textual representations: emerg, alert, crit, err, warning, notice, info, and debug. -s, --stop-exec-queue Signal systemd-udevd to stop executing new events. Incoming events will be queued. -S, --start-exec-queue Signal systemd-udevd to enable the execution of events. -R, --reload Signal systemd-udevd to reload the rules files and other databases like the kernel module index. Reloading rules and databases does not apply any changes to already existing devices; the new configuration will only be applied to new events. -p, --property=KEY=value Set a global property for all events. -m, --children-max=value Set the maximum number of events, systemd-udevd will handle at the same time. --timeout=seconds The maximum number of seconds to wait for a reply from systemd-udevd. -h, --help Print help text. udevadm monitor [options] Listens to the kernel uevents and events sent out by a udev rule and prints the devpath of the event to the console. It can be used to analyze the event timing, by comparing the timestamps of the kernel uevent and the udev event. -k, --kernel Print the kernel uevents. -u, --udev Print the udev event after the rule processing. -p, --property Also print the properties of the event. -s, --subsystem-match=string[/string] Filter events by subsystem[/devtype]. Only udev events with a matching subsystem value will pass. -t, --tag-match=string Filter events by property. Only udev events with a given tag attached will pass. -h, --help Print help text. udevadm test [options] [devpath] Simulate a udev event run for the given device, and print debug output. -a, --action=string The action string. -N, --resolve-names=early|late|never Specify when udevadm should resolve names of users and groups. When set to early (the default), names will be resolved when the rules are parsed. When set to late, names will be resolved for every event. When set to never, names will never be resolved and all devices will be owned by root. -h, --help Print help text. udevadm test-builtin [options] [command] [devpath] Run a built-in command COMMAND for device DEVPATH, and print debug output. -h, --help Print help text.SEE ALSOudev(7), systemd-udevd.service(8)How do I know if udev is running?To check whether mdev is working or not , First check in /sbin/ whether mdev is present or not. If it is not present then probably mdev is not configured properly, or else if it is present then check whether hotplug handler has been set properly. i.e inside /proc/sys/kernel/hotplug it should be /sbin/mdev written.
What is udev used for?udev is a replacement for the Device File System (DevFS) starting with the Linux 2.6 kernel series. It allows you to identify devices based on their properties, like vendor ID and device ID, dynamically. udev runs in userspace (as opposed to devfs which was executed in kernel space).
What are udev events?An introduction to Udev: The Linux subsystem for managing device events. Create a script that triggers your computer to do a specific action when a specific device is plugged in. Udev is the Linux subsystem that supplies your computer with device events.
How do you add a udev rule in Linux?There are two main locations in which those files can be placed: /usr/lib/udev/rules. d it's the directory used for system-installed rules, /etc/udev/rules. d/ is reserved for custom made rules. The files in which the rules are defined are conventionally named with a number as prefix (e.g 50-udev-default.
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