[Bug 1893716] Re: scripts in /etc/update-motd.d/ run even on login via non-interactive scp and sftp sessions

[Christian Ehrhardt ]

#2 95-hwe-eol / update-motd-hwe-eol

Sadly this already does some caching in update-motd-hwe-eol by checking
if the last of these checks is older than an update to the source lists.
But to do so it has already executed the - relatively - rather expensive
apt-config calls.

Since it comes down to checking new sources.lists there is no need to
update this more often than once every few minutes or hours. Could be
even slower without loosing most of its value, but we already achieve
most of what we need with a delay of ~1h.

We started with:
     5.37%  apt-config
Now:
     -- no more present


--- orig/95-hwe-eol	2022-03-30 07:53:18.396529018 +0000
+++ /etc/update-motd.d/95-hwe-eol	2022-03-30 09:13:16.160985148 +0000
@@ -1,5 +1,11 @@
 #!/bin/sh
 
+# this stamp is created and updated by /usr/lib/update-notifier/update-motd-hwe-eol
+stamp="/var/lib/update-notifier/hwe-eol"
+
+# do not try to refresh this more than once per hour
+find $stamp -newermt 'now-1 hours' 2> /dev/null | grep -m 1 '.' && exit 0
+
 if [ -x /usr/lib/update-notifier/update-motd-hwe-eol ]; then
     exec /usr/lib/update-notifier/update-motd-hwe-eol
 fi


No big need left to reduce the apt-config usage in update-motd-hwe-eol after this change.

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https://bugs.launchpad.net/bugs/1893716

Title:
  scripts in /etc/update-motd.d/ run even on login via non-interactive
  scp and sftp sessions

Status in landscape-client package in Ubuntu:
  New
Status in pam package in Ubuntu:
  Confirmed
Status in ubuntu-release-upgrader package in Ubuntu:
  New
Status in update-motd package in Ubuntu:
  Confirmed
Status in update-notifier package in Ubuntu:
  New

Bug description:
  My client has 200+ devices automatically uploading information via
  sftp and scp to a server every few minutes. After a recent update, I
  noticed the load on their server spiking through the roof. Upon
  investigation, I discovered a horde of landscape-sysinfo and
  /usr/bin/lsb_release processes running that correlated with login
  session notifications in /var/log/syslog and the load spikes.

  It appears that even in non-interactive sessions where this
  information will never be seen, the configuration options below in
  /etc/pam.d/sshd cause these items to be launched (in fact, probably
  everything in /etc/update-motd.d). This only started on the system in
  question after a recent set of system updates were installed.

  The content of /etc/update-motd.d/* really, really, really shouldn't
  be executed if the session in question is not interactive, as it
  provides no value at all. Unfortunately, to disable it for these non-
  interactive sessions, we also have to disable it for the interactive
  ones as well where it has some value (though not enough to make
  spiking the load on this server through the roof an acceptable
  tradeoff).

  # Print the message of the day upon successful login.
  # This includes a dynamically generated part from /run/motd.dynamic
  # and a static (admin-editable) part from /etc/motd.
  #session    optional     pam_motd.so  motd=/run/motd.dynamic
  #session    optional     pam_motd.so noupdate

  Also, looking at the script 00-header in /etc/update-motd.d/,
  /usr/bin/lsb_release is being improperly launched, as /etc/lsb_release
  does include the necessary information:

  [ -r /etc/lsb-release ] && . /etc/lsb-release

  if [ -z "$DISTRIB_DESCRIPTION" ] && [ -x /usr/bin/lsb_release ]; then
          # Fall back to using the very slow lsb_release utility
          DISTRIB_DESCRIPTION=$(lsb_release -s -d)
  fi

  # cat /etc/lsb-release
  DISTRIB_ID=Ubuntu
  DISTRIB_RELEASE=16.04
  DISTRIB_CODENAME=xenial
  DISTRIB_DESCRIPTION="Ubuntu 16.04.7 LTS"

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