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 target units state. Receiving this alert indicates that one
or more of the systemd target units are in the failed state.
Read more about systemd
Here is some useful information about systemd from wikipedia 1
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.
See more on systemd.target units
Target units file ends with the
.targetfile extension and their only purpose is to group together
other systemd units through a chain of dependencies. For example, the graphical.target unit, which
is used to start a graphical session, starts system services such as the GNOME Display Manager (
gdm.service) or Accounts Service (accounts-daemon .service) and also activates the multi-user.target
unit. Similarly, the multi-user.target unit starts other essential system services such as NetworkManager (NetworkManager.service) or D-Bus (dbus.service) and activates another target unit named basic.target. 2
Among other things, target units are a more flexible replacement for SysV runlevels in the classic
SysV init system. For compatibility reasons special target units such as runlevel3.target exist which are used by the SysV runlevel compatibility code in systemd.
References and source
When a target is in a failed state, you should always try to gather more information about it.
Identify which target units fail. Open the Netdata dashboard, find the current active alarms under
the active alarms tab and look into its chart. (
systemdunits_target_units.target_unit_state). In this chart, identify which target units are in state with value 5
Gather more information about the failing target unit
root@netdata~ # systemctl status <target_name>.target
Check the log messages from the command of step 2.