[Bug 1803601] Re: motd-news.service scheduled even when /etc/update-motd.d/50-motd-news is not executable

[Simon Déziel]

A possible fix would be to make the unit execution conditional to the
update-motd fragment being executable:

  [Unit]
  ConditionFileIsExecutable=/etc/update-motd.d/50-motd-news

I'm not sure if this should be added to motd-news.service, motd-
news.timer or both.

** Description changed:

  update-motd(5) says:
  
-  Executable scripts in /etc/update-motd.d/* are executed by pam_motd(8) as the root user at each 
-  login, and this information is concatenated in /run/motd.dynamic.  The order of  script  execu‐
-  tion is determined by the run-parts(8) --lsbsysinit option (basically alphabetical order, with
-  a few caveats).
+  Executable scripts in /etc/update-motd.d/* are executed by pam_motd(8) as the root user at each
+  login, and this information is concatenated in /run/motd.dynamic.  The order of  script  execu‐
+  tion is determined by the run-parts(8) --lsbsysinit option (basically alphabetical order, with
+  a few caveats).
  
  So sysadmins are used to "chmod -x" motd fragments from /etc/update-
  motd.d/ to prevent their execution. When doing so for /etc/update-
  motd.d/50-motd-news, I noticed that motd-news.timer was still trying to
  execute the motd-news.service unit which then logged a failure:
  
-  systemd[3704]: motd-news.service: Failed to execute command: Permission denied
-  systemd[3704]: motd-news.service: Failed at step EXEC spawning /etc/update-motd.d/50-motd-news:
-   Permission denied
-  systemd[1]: motd-news.service: Main process exited, code=exited, status=203/EXEC
-  systemd[1]: motd-news.service: Failed with result 'exit-code'.
-  systemd[1]: Failed to start Message of the Day.
+  systemd[3704]: motd-news.service: Failed to execute command: Permission denied
+  systemd[3704]: motd-news.service: Failed at step EXEC spawning /etc/update-motd.d/50-motd-news:
+   Permission denied
+  systemd[1]: motd-news.service: Main process exited, code=exited, status=203/EXEC
+  systemd[1]: motd-news.service: Failed with result 'exit-code'.
+  systemd[1]: Failed to start Message of the Day.
+ 
+ 
+ The motd-news.service unit looks like this:
+ 
+ $ systemctl cat motd-news.service
+ # /lib/systemd/system/motd-news.service
+ [Unit]
+ Description=Message of the Day
+ After=network-online.target
+ Documentation=man:update-motd(8)
+ 
+ [Service]
+ Type=oneshot
+ ExecStart=/etc/update-motd.d/50-motd-news --force
  
  
  This problem was observed on a Bionic system:
  
  $ lsb_release -rd
  Description:	Ubuntu 18.04.1 LTS
  Release:	18.04
  $ apt-cache policy base-files
  base-files:
-   Installed: 10.1ubuntu2.3
-   Candidate: 10.1ubuntu2.3
-   Version table:
-  *** 10.1ubuntu2.3 500
-         500 http://archive.ubuntu.com/ubuntu bionic-updates/main amd64 Packages
-         100 /var/lib/dpkg/status
-      10.1ubuntu2.2 500
-         500 http://security.ubuntu.com/ubuntu bionic-security/main amd64 Packages
-      10.1ubuntu2 500
-         500 http://archive.ubuntu.com/ubuntu bionic/main amd64 Packages
+   Installed: 10.1ubuntu2.3
+   Candidate: 10.1ubuntu2.3
+   Version table:
+  *** 10.1ubuntu2.3 500
+         500 http://archive.ubuntu.com/ubuntu bionic-updates/main amd64 Packages
+         100 /var/lib/dpkg/status
+      10.1ubuntu2.2 500
+         500 http://security.ubuntu.com/ubuntu bionic-security/main amd64 Packages
+      10.1ubuntu2 500
+         500 http://archive.ubuntu.com/ubuntu bionic/main amd64 Packages
  
  But the problem also exist in Disco.

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https://bugs.launchpad.net/bugs/1803601

Title:
  motd-news.service scheduled even when /etc/update-motd.d/50-motd-news
  is not executable

Status in base-files package in Ubuntu:
  New

Bug description:
  update-motd(5) says:

   Executable scripts in /etc/update-motd.d/* are executed by pam_motd(8) as the root user at each
   login, and this information is concatenated in /run/motd.dynamic.  The order of  script  execu‐
   tion is determined by the run-parts(8) --lsbsysinit option (basically alphabetical order, with
   a few caveats).

  So sysadmins are used to "chmod -x" motd fragments from /etc/update-
  motd.d/ to prevent their execution. When doing so for /etc/update-
  motd.d/50-motd-news, I noticed that motd-news.timer was still trying
  to execute the motd-news.service unit which then logged a failure:

   systemd[3704]: motd-news.service: Failed to execute command: Permission denied
   systemd[3704]: motd-news.service: Failed at step EXEC spawning /etc/update-motd.d/50-motd-news:
    Permission denied
   systemd[1]: motd-news.service: Main process exited, code=exited, status=203/EXEC
   systemd[1]: motd-news.service: Failed with result 'exit-code'.
   systemd[1]: Failed to start Message of the Day.

  
  The motd-news.service unit looks like this:

  $ systemctl cat motd-news.service
  # /lib/systemd/system/motd-news.service
  [Unit]
  Description=Message of the Day
  After=network-online.target
  Documentation=man:update-motd(8)

  [Service]
  Type=oneshot
  ExecStart=/etc/update-motd.d/50-motd-news --force

  
  This problem was observed on a Bionic system:

  $ lsb_release -rd
  Description:	Ubuntu 18.04.1 LTS
  Release:	18.04
  $ apt-cache policy base-files
  base-files:
    Installed: 10.1ubuntu2.3
    Candidate: 10.1ubuntu2.3
    Version table:
   *** 10.1ubuntu2.3 500
          500 http://archive.ubuntu.com/ubuntu bionic-updates/main amd64 Packages
          100 /var/lib/dpkg/status
       10.1ubuntu2.2 500
          500 http://security.ubuntu.com/ubuntu bionic-security/main amd64 Packages
       10.1ubuntu2 500
          500 http://archive.ubuntu.com/ubuntu bionic/main amd64 Packages

  But the problem also exist in Disco.

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