[Bug 1821343] [NEW] slapd process failure is not detected by systemd

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[Impact]
Systemd service reports slapd as active, even though it may have failed

[Description]
The slapd package for OpenLDAP is shipped with a SysV-style init script (/etc/init.d/slapd). Systemd automatically converts this to a systemd service by generating the unit file using the systemd-sysv-generator(8) utility. The generated unit file contains Type=forking and RemainAfterExit=yes directives.

If the slapd daemon process exits due to some failure (e.g., it receives
a SIGTERM or SIGKILL), the failure is not detected properly by systemd.
The service is still reported as active even though the child (daemon)
process has exited with a signal.

We can easily fix this by including a proper systemd service file for
slapd in the openldap package. Since the init.d script already does most
of the necessary work (parsing configs, setting up PID files, etc.), we
don't need anything complicated for the systemd unit file. Just making
sure that RemainAfterExit is set to "no" makes the systemd service
behave in the expected way.

[Test Case]
1) Deploy a disco container
$ lxc launch images:ubuntu/disco disco

2) Install slapd
ubuntu at disco:~$ sudo apt update && sudo apt install slapd -y

3) Verify that slapd is running with the auto-generated service
ubuntu at disco:~$ systemctl status slapd
● slapd.service - LSB: OpenLDAP standalone server (Lightweight Directory Access Protocol)
   Loaded: loaded (/etc/init.d/slapd; generated)
   Active: active (running) since Fri 2019-03-22 11:51:22 UTC; 40min ago
     Docs: man:systemd-sysv-generator(8)
  Process: 1103 ExecStart=/etc/init.d/slapd start (code=exited, status=0/SUCCESS)
    Tasks: 3 (limit: 4915)
   Memory: 712.6M
   CGroup: /system.slice/slapd.service
           └─1109 /usr/sbin/slapd -h ldap:/// ldapi:/// -g openldap -u openldap -F /etc/ldap/slapd.d

4) SIGKILL the slapd process (PID is displayed in systemctl status output)
ubuntu at disco:~$ sudo kill -9 1109

5) Check if systemd service lists slapd as still active, even though it was terminated
ubuntu at disco:~$ systemctl status slapd
● slapd.service - LSB: OpenLDAP standalone server (Lightweight Directory Access Protocol)
   Loaded: loaded (/etc/init.d/slapd; generated)
   Active: active (exited) since Fri 2019-03-22 11:51:22 UTC; 42min ago
     Docs: man:systemd-sysv-generator(8)
  Process: 1103 ExecStart=/etc/init.d/slapd start (code=exited, status=0/SUCCESS)

[Regression Potential]
The regression potential for this fix should be very low, if we keep the new systemd unit file close to the one generated by systemd-sysv-generator(8). The only significant change would be the RemainAfterExit directive, and this should make the slapd service behave like a "normal" forking service. Nonetheless, we'll perform scripted test runs to make sure no regressions arise.

** Affects: openldap (Ubuntu)
     Importance: Medium
     Assignee: Heitor R. Alves de Siqueira (halves)
         Status: Confirmed

** Affects: openldap (Ubuntu Xenial)
     Importance: Medium
     Assignee: Heitor R. Alves de Siqueira (halves)
         Status: Confirmed

** Affects: openldap (Ubuntu Bionic)
     Importance: Medium
     Assignee: Heitor R. Alves de Siqueira (halves)
         Status: Confirmed

** Affects: openldap (Ubuntu Cosmic)
     Importance: Medium
     Assignee: Heitor R. Alves de Siqueira (halves)
         Status: Confirmed


** Tags: patch sts sts-sponsor
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slapd process failure is not detected by systemd
https://bugs.launchpad.net/bugs/1821343
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