Linux | Systemd units
Systemd is a suite of basic building blocks for a Linux system. It provides a system and service manager that runs as PID 1 and starts the rest of the system.
The Netdata Agent monitors the
systemd.device units. The
systemd_device_units_state alert indicates that one or more of the
systemd.device units have failed. A systemd device unit “failed” when the service process returned error code on exit, or crashed, an operation timed out, or after too many restarts. The cause of a failed states is stored in a log.
Read More About systemd
Here is some useful information about systemd from
Systemd includes features like on-demand starting of daemons, snapshot support, process tracking, and Inhibitor Locks. Systemd is not just the name of the
init daemon, but also refers to the entire software bundle around it, which, in addition to the
init daemon, includes the daemons
networkd, and many other low-level components. In January 2013, Poettering described systemd not as one program, but rather a large software suite that includes 69 individual binaries. As an integrated software suite, systemd replaces the startup sequences and runlevels controlled by the traditional
init daemon, along with the shell scripts executed under its control. systemd also integrates many other services that are common on Linux systems by handling user logins, the system console, device hotplugging, scheduled execution (replacing cron), logging, hostnames and locales.
systemd is a daemon that manages other daemons, which, including
itself, are background processes.
systemd is the first daemon to start during booting and the last daemon to terminate during shutdown. The
systemd daemon serves as the root of the user space’s process tree. The first process (
PID1) has a special role on Unix systems, as it replaces the parent of a process when the original parent terminates. Therefore, the first process is particularly well suited for the purpose of monitoring daemons.
Systemd executes elements of its startup sequence in parallel, which is theoretically faster than the traditional startup sequence approach. For inter-process communication (IPC),
systemd makes Unix domain sockets and D-Bus available to the running daemons. The state of systemd itself can also be preserved in a snapshot for future recall.
Systemd’s core components include the following:
systemdis a system and service manager for Linux operating systems.
systemctlis a command to introspect and control the state of the systemd system and service
manager. Not to be confused with sysctl.
systemd-analyzemay be used to determine system boot-up performance statistics and retrieve
other state and tracing information from the system and service manager.
More On systemd-`.device` Units
A unit configuration file whose name ends in
.device encodes information about a device unit as exposed in the
sysfs/udev(7) device tree.
udev provides a dynamic device directory containing only the files for actually present devices. It creates or removes device node files in the
/dev directory, or it renames network interfaces.
This unit type has no specific options. Device units are named after the
/dev paths they control. For example, the device
/dev/sda5 is exposed in systemd as
If a device has failed, then you should always try to gather more information about the cause of the failure.
Identify which device units fail. Open the Netdata dashboard, find the current active alarms under the active alarms tab and look into its chart (
systemdunits_device_units.device_unit_state). In this chart, identify which device units are in state with value 5.
Check the status of the device
root@netdata~ # systemctl status <device_name>.device