udevadm

Monitor all device events

$ sudo udevadm monitor

$ sudo udevadm monitor [[-k|--kernel]]

$ sudo udevadm monitor [[-u|--udev]]

$ sudo udevadm info [[-a|--attribute-walk]] [/dev/sda]

$ sudo udevadm control [[-R|--reload]]

$ sudo udevadm trigger

$ sudo udevadm test [/dev/sda]

udevadm [--version] [--help] | subcommand [options] [arguments]

--debug
    Enable extended output with debug messages

--version
    Print program version and exit

--help
    Print help text and exit

control
    Query or set udev daemon parameters at runtime

help
    Print help for specified subcommand

hwdb
    Query or update hardware database

info
    Print device information from sysfs or kernel

monitor
    Listen to kernel uevents and udev events

query
    Query udev properties from database file

settle
    Wait for ongoing device events to complete

test
    Simulate a device uevent through udev

test-builtin
    Test a built-in udev command

trigger
    Request events for currently available devices

version
    Print udev and kernel versions

udevadm is the administrative command-line utility for interacting with udev(7), the Linux kernel's device manager. It allows querying device properties, monitoring hardware events, testing rules, triggering uevents, and controlling the udev daemon.

Key functionalities include inspecting sysfs attributes (info), watching kernel uevents and udev settlements (monitor), simulating device hotplug (trigger), and validating rule syntax (test). It's invaluable for debugging device detection, persistent naming issues, or hardware database lookups via hwdb.

Primarily used by system administrators and developers on systemd-based distributions, it provides direct access to the device event subsystem without restarting services. Global options like --debug aid troubleshooting, while subcommands handle specific tasks. Output is typically human-readable but supports structured formats for scripting.

Many subcommands require root privileges; trigger and test can disrupt devices if misused. Debug output may be verbose. Not for production event triggering.

udevadm info /sys/block/sda – Show device properties.
udevadm monitor – Watch uevents live.
udevadm trigger --type=devices --action=change – Re-enumerate devices.

Each subcommand has unique flags, e.g., info --query=property, monitor --kernel, hwdb --update. Run udevadm <subcommand> --help for details.

Developed as part of udev project (2003) by Gentoo developers; integrated into systemd (2012). Replaced legacy tools like udevinfo(8), udevtest(8). Evolved with eudev fork and systemd-udev.

udev(7), systemd-udevd(8), udev.rules(7), lsblk(8), lspci(8)