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Asked: 2018-10-25 06:22:08 +0800 CST

Cannot use `systemctl --user` due to "Failed to get D-bus connection: permission denied"

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I'm trying to set up user-level services, using this answer to a similar question. I have create the required files and rebooted.

I'm making progress because I now get "Failed to get D-bus connection: permission denied" when it was "Failed to get D-bus connection: connection refused", but I'm stumped because I don't know what object it is trying to access (file? socket?) and so cannot even check current permissions. Any ideas?

So far I have added:

loginctl enable-linger userservice

/usr/lib/systemd/user/dbus.service (-rw-r--r-- root root)

[Unit]
Description=D-Bus User Message Bus
Requires=dbus.socket

[Service]
ExecStart=/usr/bin/dbus-daemon --session --address=systemd: --nofork --nopidfile --systemd-activation
ExecReload=/usr/bin/dbus-send --print-reply --session --type=method_call --dest=org.freedesktop.DBus / org.freedesktop.DBus.ReloadConfig

[Install]
Also=dbus.socket

/usr/lib/systemd/user/dbus.socket (-rw-r--r-- root root)

[Unit]
Description=D-Bus User Message Bus Socket

[Socket]
ListenStream=%t/bus
ExecStartPost=-/bin/systemctl --user set-environment DBUS_SESSION_BUS_ADDRESS=unix:path=%t/bus

[Install]
WantedBy=sockets.target
Also=dbus.service

/home/userservice/.config/systemd/user/userservice.service

[Unit]
Description=Test user-level service

[Service]
Type=dbus
BusName=com.wtf.service
ExecStart=/home/userservice/userservice.py
Restart=on-failure

[Install]
WantedBy=default.target

Not added any links elsewhere...

To make it fail:

systemctl --user status

Edit 2018-10-25:

Added export XDG_RUNTIME_DIR=/run/user/$(id -u) to .bashrc. The variable is set and now I get: Failed to get D-us connection: no such file or directory. Strangely, neither man systemctl nor systemctl --help mention the --user option, while both mention --system and specify that this is the default (so what are the other options).

Using RHEL 7.4 (with systemd 219 as reported by systemctl --version) with SELinux.

systemd

3 Answers

  1. I've noticed the tableau server uses --user systemd services - they even have a note about this in their docs: https://help.tableau.com/current/server-linux/en-us/systemd_user_service_error.htm

    The systemd user service is not used as commonly as the normal systemd process manager. Red Hat disabled the systemd user service in RHEL 7 (and thereby all distros that come from RHEL, like CentOS, Oracle Linux 7, Amazon Linux 2). However, RedHat has assured Tableau that running the systemd user service is supported as long as the service is re-enabled.

    How they do it (example is with a userid 29575)

    # cat /etc/systemd/system/[email protected]
[Unit]
Description=User Manager for UID %i
After=systemd-user-sessions.service
# These are present in the RHEL8 version of this file except that the unit is Requires, not Wants.
# It's listed as Wants here so that if this file is used in a RHEL7 settings, it will not fail.
# If a user upgrades from RHEL7 to RHEL8, this unit file will continue to work until it's
# deleted the next time they upgrade Tableau Server itself.
After=user-runtime-dir@%i.service
Wants=user-runtime-dir@%i.service

[Service]
LimitNOFILE=infinity
LimitNPROC=infinity
User=%i
PAMName=systemd-user
Type=notify
# PermissionsStartOnly is deprecated and will be removed in future versions of systemd
# This is required for all systemd versions prior to version 231
PermissionsStartOnly=true
ExecStartPre=/bin/loginctl enable-linger %i
ExecStart=-/lib/systemd/systemd --user
Slice=user-%i.slice
KillMode=mixed
Delegate=yes
TasksMax=infinity
Restart=always
RestartSec=15

[Install]
WantedBy=default.target

    After you create that file:

    systemctl daemon-reload
systemctl enable [email protected]
systemctl start [email protected]

    And you'll need to set XDG_RUNTIME_DIR in env of that user via bashrc or similar:

    [ -z "${XDG_RUNTIME_DIR}" ] && export XDG_RUNTIME_DIR=/run/user/$(id -ru)

    I've tested in on a recent RHEL 7.8 and it works as expected, I can run "systemctl --user status" as my user after doing this.

    • 10

  2. So there's a long standing issue where the XDG_RUNTIME_DIR environment variable doesn't get set properly, or at all, when users log in, and therefore can't access the user D-Bus. This happens when the user logs in via some other method than the local graphical console.

    You can work around this by adding to the user's $HOME/.bashrc:

    export XDG_RUNTIME_DIR=/run/user/$(id -u)

    Then log out and back in.

    • 9

  3. You should be aware of how the PAM works.

    If you login in the system using either of

    1. graphical session
    2. login on terminal (username and password)
    3. ssh

    then the PAM machinery will call pam_systemd, and this will setup all needed hooks to use systemctl; if you switch user using sudo or su, this will not happen.

    This is deliberate , see https://github.com/systemd/systemd/issues/7451#issuecomment-346787237

    What's weird is that actually /etc/pam.d/su includes /etc/pam.d/common-session that contains an invocation of pam_systemd but this fails, indeed the /var/log/auth.log says:

    pam_systemd(su:session): Cannot create session: Already running in a session

    Currently, a good way is to use ssh to connect to the same machine but as another user, something like ssh user@localhost.

    • 5