Hello Thomas,
Thanks for reporting this and making Ubuntu better.
about your statement on lsb-release, in 00-header:
""""
[ -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"
""""
the slowpath is only executed if the DISTRIB_DESCRIPTION variable is not
set, at least in my tests.
In regards to your statement:
"""
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).
"""
Considering there IS a way of disabling the dynamic motd contents
currently by commenting only the line containing the /run/motd.dynamic
wording:
# 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
I'm flagging this bug as a whishlist priority.
** Also affects: update-motd (Ubuntu)
Importance: Undecided
Status: New
** No longer affects: openssh (Ubuntu)
** No longer affects: base-files (Ubuntu)
** Changed in: update-motd (Ubuntu)
Status: New => Triaged
** Changed in: update-motd (Ubuntu)
Importance: Undecided => Wishlist
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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 update-motd package in Ubuntu:
Triaged
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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