Managing SQL Server 2019 service on Ubuntu with systemctl

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Introduction

SQL Server 2019 is installed on Ubuntu 18.04. In the default architecture, SQL Server 2019 runs with the account mssql.

Architecture SQL Server 2019 - Linux Ubuntu

With the account mssql, the status of the service mssql-server is easily reported :

mssql@vps$ systemctl status mssql-server
           mssql-server.service - Microsoft SQL Server Database Engine
   Loaded: loaded (/lib/systemd/system/mssql-server.service; enabled; vendor preset: enabled)
   Active: active (running) since Tue 2019-05-31 11:20:09 CEST; 36min ago
     Docs: https://docs.microsoft.com/en-us/sql/linux
 Main PID: 1448 (sqlservr)
    Tasks: 182
   CGroup: /system.slice/mssql-server.service
           ├─1448 /opt/mssql/bin/sqlservr
           └─1460 /opt/mssql/bin/sqlservr

But when trying to stop/start/restart the service mssql-server with systemctl, the password is prompted.

mssql@vps$ systemctl stop mssql-server
          ==== AUTHENTICATING FOR org.freedesktop.systemd1.manage-units ===
Authentication is required to stop 'mssql-server.service'.
Multiple identities can be used for authentication:
 1.  Ubuntu (ubuntu)
 2.  mssql
Choose identity to authenticate as (1-2):
mssql@vps$ sudo systemctl stop mssql-server
          [sudo] password for mssql:

We may want to allow mssql to manage its own service without password prompts.

2 solutions are available :

  • Defining mssql-server as a user service with the account mssql.
  • Granting rights with no password on the system service mssql-server to the user mssql through sudo.

Solution 1 : Defining mssql-server as a user service with the account mssql

By default the system service mssql-server is defined in the file /lib/systemd/system/mssql-server.service. It is a basic configuration for a service.

/lib/systemd/system/mssql-server.service
[Unit]
Description=Microsoft SQL Server Database Engine
After=network.target auditd.service
Documentation=https://docs.microsoft.com/en-us/sql/linux

[Service]
ExecStart=/opt/mssql/bin/sqlservr
User=mssql
WorkingDirectory=/var/opt/mssql

# Kill root process
KillMode=process

# Wait up to 30 minutes for service to start/stop
TimeoutSec=30min

# Remove process, file, thread limits
#
LimitNPROC=infinity
LimitNOFILE=infinity
TasksMax=infinity
UMask=007

# Restart on non-successful exits.
Restart=on-failure

# Don't restart if we've restarted more than 3 times in 2 minutes.
StartLimitInterval=120
StartLimitBurst=3

[Install]
WantedBy=multi-user.target

Instead of using a system service, a switch to a user service as user mssql is performed.

The system service mssql-server is first stopped and disabled as root :

root@vps$ systemctl stop mssql-server
          
root@vps$ systemctl disable mssql-server
          
root@vps$ systemctl daemon-reload

As mssql, the file /lib/systemd/system/mssql-server.service is copied in the directory $HOME/.config/systemd/user (service user directory).

mssql@vps$ mkdir -p  $HOME/.config/systemd/user

mssql@vps$ cp /lib/systemd/system/mssql-server.service $HOME/.config/systemd/user

In this copied file, 2 updates :

$HOME/.config/systemd/user/mssql-server.service
…
[Service]
# User=mssql
…
…
[Install]
WantedBy=default.target

The directive User=mssql is commented out, if not, an error message is raised about the group during the fork.

  Process: 1904 ExecStart=/opt/mssql/bin/sqlservr (code=exited, status=216/GROUP)
 Main PID: 1904 (code=exited, status=216/GROUP)

If we want this user service to start at boot, the directive WantedBy must be set to default.target and not multi-user.target, the last one is only effective for a system service at boot time.

At this stage, the user service can be managed by mssql, without password prompts, systemctl is invoked with the option --user :

mssql@vps$ systemctl --user daemon-reload
          
mssql@vps$ systemctl --user status mssql-server
          ● mssql-server.service - Microsoft SQL Server Database Engine
   Loaded: loaded (/home/mssql/.config/systemd/user/mssql-server.service; disabled; vendor preset: enabled)
   Active: inactive (dead)
mssql@vps$ systemctl --user start|stop|restart mssql-server

Last step, enable the user service mssql-server at boot time :

mssql@vps$ systemctl --user enable mssql-server

Don’t forget to allow the user mssql to run services when it is not logged in, to do so, as root :

root@vps$ loginctl enable-linger mssql

Solution 2 : Granting rights with no password on the system service mssql-server to the user mssql through sudo

If you want to keep the service mssql-server as a system one, edit the file /etc/sudoers with visudo.

root@vps$ visudo

Add the following authorizations for the user mssql in this file :

Cmnd_Alias MSSQL_CMDS = /bin/systemctl start mssql-server, /bin/systemctl stop mssql-server
mssql ALL=(root) NOPASSWD: MSSQL_CMDS

Use the full path /bin/systemctl, it is recommended in the sudoers fils.

The user mssql can now manage the system service mssql-server without being prompted for the password :

mssql@vps$ sudo systemctl start|stop mssql-server

Conclusion

To manage the service mssql-server with the account mssql, two easy solutions. It depends essentially on the preferred way or any enterprise and security constraints.