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

[Simon Déziel]

Public bug reported:

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.


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.

** Affects: base-files (Ubuntu)
     Importance: Undecided
         Status: New

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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.

  
  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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