Problem Description:

When using $sudo status docker to check the state of the docker daemon, the following error was encountered:

status: cannot connect to Upstart: Failed to connect to socket /com/ubuntu/upstart: connect denied

The causes are as follows

Google found that ubntun no longer supports upstart

SYSTEMd is the latest init in Linux system. Its main design goal is to overcome the inherent shortcomings of sysvinit and improve the startup speed of the system. Upstart of SYSTEMd and Ubuntu are competitors and will replace upstart. In fact, the author’s Ubuntu 16.04 lts has adopted SYSTEMd as its standard system initialization system

SYSTEMd is a kind of init software under Linux, a system and service manager under Linux, compatible with SYSV and LSB startup scripts. Led by Lennart poetering and released under LGPL 2.1 and its subsequent licenses, the development goal is to provide a better framework to express the dependency relationship between system services, and to realize the parallel startup of services during system initialization. At the same time, it can reduce the system overhead of shell, and finally replace the commonly used init programs of System V and BSD style
compared with init, the system V style used in most distributions, SYSTEMd adopts the following new technologies:

(1) using socket activated and bus activated services to improve the parallel performance of interdependent services

(2) cgroups is used instead of PID to track the process, so that even the generated daemons after two forks will not be out of the control of SYSTEMd

The features of SYSTEMd are as follows:

Support parallel tasks; At the same time, socket and D-Bus are used to activate the service; Start the daemons on demand. The cgroups of Linux is used to monitor the process; Support snapshot and system recovery. Maintain mount point and own active mount point. Each service is precisely controlled based on the dependency relationship

Name source:

The name SYSTEMd comes from a convention in UNIX: in UNIX, “d” is often used as the suffix identification of the system daemons. In addition, SYSTEMd is also a substitute for the English term D system, which is used to describe a person’s ability to quickly adapt to the environment and solve difficulties

the main command to view and control SYSTEMd is systemctl

This command can be used to view system status and manage systems and services

Tips:
- Adding -H <username>@<hostname> to the systemctl parameter enables remote control of other machines.

This procedure uses an SSH connection.
- systemadm is the official graphical front-end for systemd. A stable version, systemd-ui, is available from the official repository.

- Plasma users can install the systemctl graphical front-end systemd-kcm.

Once installed, it can be found under System administration

Problem solving:

check whether the docker service is started:

$ systemctl status docker

if not, start the docker service:

$ sudo systemctl start docker