Failed to get D-Bus connection: Connection refused

amazon ec2d-bussystemd

A sudo user named my-host is getting the following error message when trying to reload systemctl on an Amazon Linux 2 EC2 image.

[my-host@ip-12-3-4-56 ~]$ systemctl --user daemon-reload
Failed to get D-Bus connection: Connection refused

What specifically needs to be done to resolve and remove this error?

The other postings I have found on this error message are either related to Debian with an apt-get solution that does not apply here, or are related to Docker images, which also do not apply here.

If the problem has to do with user privileges, what would need to be done to remediate the problem?

This machine has a requirement that some systemctl commands like this must not run as sudo.

TRY AGAIN WITH DIRECT LOGIN USER PER @Stewart's and @JdeBP's SUGGESTIONS:

We then tried using a sudo user that has direct ssh ability from the outside world, but still got the following results:

[ssh-login-user@ip-12-3-4-567 ~]$ systemctl --user daemon-reload
Failed to get D-Bus connection: No such file or directory
[ssh-login-user@ip-12-3-4-567 ~]$ echo $XDG_RUNTIME_DIR $UID
/run/user/1001 1001
[ssh-login-user@ip-12-3-4-567 ~]$ systemctl --user status
Failed to get D-Bus connection: No such file or directory
[ssh-login-user@ip-12-3-4-567 ~]$ sudo install -d -o ssh-login-user /run/user/`id -u ssh-login-user`
[sudo] password for ssh-login-user:
[ssh-login-user@ip-12-3-4-567 ~]$ sudo systemctl start user@`id -u ssh-login-user`
Failed to start user@1001.service: Unit not found.
[ssh-login-user@ip-12-3-4-567 ~]$ sudo -u ssh-login-user DBUS_SESSION_BUS_ADDRESS=unix:path=/run/user/`id -u ssh-login-user`/bus systemctl --user
Failed to get D-Bus connection: No such file or directory

To confirm the state of systemctl, we then also did the following, which reported one degraded service as follows:

● ip-12-3-4-567.aws-region-n.compute.internal
    State: degraded
     Jobs: 0 queued
   Failed: 1 units
    Since: Wed 2020-10-28 23:40:50 UTC; 7min ago
   CGroup: /
           ├─1 /usr/lib/systemd/systemd --switched-root --system --deserialize 22
           ├─user.slice
           │ └─user-1001.slice
           │   └─session-2.scope
           │     ├─18736 sshd: ssh-login-user [priv]
           │     ├─18738 sshd: ssh-login-user@pts/0
           │     ├─18739 -bash
           │     ├─18792 sudo systemctl status
           │     └─18793 systemctl status
           └─system.slice
             ├─rngd.service
             │ └─2692 /sbin/rngd -f
             ├─amazon-ssm-agent.service
             │ ├─3810 /usr/bin/amazon-ssm-agent
             │ └─4428 /usr/bin/ssm-agent-worker
             ├─libstoragemgmt.service
             │ └─2694 /usr/bin/lsmd -d
             ├─systemd-udevd.service
             │ └─1968 /usr/lib/systemd/systemd-udevd
             ├─system-serial\x2dgetty.slice
             │ └─serial-getty@ttyS0.service
             │   └─3273 /sbin/agetty --keep-baud 115200,38400,9600 ttyS0 vt220
             ├─chronyd.service
             │ └─2685 /usr/sbin/chronyd
             ├─auditd.service
             │ └─2646 /sbin/auditd
             ├─systemd-journald.service
             │ └─1931 /usr/lib/systemd/systemd-journald
             ├─atd.service
             │ └─3239 /usr/sbin/atd -f
             ├─sshd.service
             │ └─3486 /usr/sbin/sshd -D
             ├─crond.service
             │ └─3529 /usr/sbin/crond -n
             ├─gssproxy.service
             │ └─2711 /usr/sbin/gssproxy -D
             ├─rsyslog.service
             │ └─3229 /usr/sbin/rsyslogd -n
             ├─rpcbind.service
             │ └─2683 /sbin/rpcbind -w
             ├─network.service
             │ ├─2919 /sbin/dhclient -q -lf /var/lib/dhclient/dhclient--eth0.lease -pf /var/run/dhclient-eth0.pid eth0
             │ └─3034 /sbin/dhclient -6 -nw -lf /var/lib/dhclient/dhclient6--eth0.lease -pf /var/run/dhclient6-eth0.pid eth0
             ├─lvm2-lvmetad.service
             │ └─1953 /usr/sbin/lvmetad -f
             ├─postfix.service
             │ ├─3177 /usr/libexec/postfix/master -w
             │ ├─3178 pickup -l -t unix -u
             │ └─3179 qmgr -l -t unix -u
             ├─acpid.service
             │ └─3456 /usr/sbin/acpid
             ├─dbus.service
             │ └─2681 /usr/bin/dbus-daemon --system --address=systemd: --nofork --nopidfile --systemd-activation
             ├─system-getty.slice
             │ └─getty@tty1.service
             │   └─3274 /sbin/agetty --noclear tty1 linux
             └─systemd-logind.service
               └─2686 /usr/lib/systemd/systemd-logind

What else can we do to resolve this problem?

ANSWER: We decided to continue running systemctl as sudo and instead to just specify the user in the .service file so that the service will run as the specified user and not as root or sudo. We chose this approach because the answers below did not resolve the problem.

Best Answer

How are you logging in as my-host?

If it's with su, I found that /run/user/$UID isn't created and XDG_RUNTIME_DIR isn't updated.

user ~ $ echo $XDG_RUNTIME_DIR $UID
/run/user/1000 1000

user ~ $ su my-host

my-host ~ $ echo $XDG_RUNTIME_DIR $UID
/run/user/1000 1001                     <-- Mismatch here! 

my-host ~ $ systemctl --user status
Failed to connect to bus: Permission denied

Because $XDG_RUNTIME_DIR isn't changed, systemd is trying to connect to the user runtime of your original user which my-host doesn't have permissions for.

Per the systemd devs:

"su" is a tool for changing user identities and very few other process credentials temporarily. It's not a tool for opening a completely new login session. A new login session has a very well defined, pristine setup, not inheriting anything from any other session, but this is really not the case for "su" uid changes: most of the execution environment is inherited over, in numerous and non-obvious ways, for example MAC contexts, audit contexts, cgroup contexts, namespace contexts, scheduling, timer granularity,

The answer is to login as my-host with a totally fresh session. Ways to do that:

  1. reboot
  2. Exit to your display manager and login again
  3. machinectl login
  4. ssh my-host@127.0.0.1

I've seen other posts which do things like mkdir /run/user/$(id -u) and manually set environment variables such as XDG_RUNTIME_DIR and DBUS_SESSION_BUS_ADDRESS, but the most reliable way is to simply change how you login. A clean login will do all of that for you.

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