[Bug 1873545] Re: Permission denied error from show-motd when updates available

[Hayden Barnes]

/etc/update-motd.d/91-release-upgrade:

 #!/bin/sh

 # if the current release is under development there won't be a new one
 if [ "$(lsb_release -sd | cut -d' ' -f4)" = "(development" ]; then
    exit 0
 fi
 if [ -x /usr/lib/ubuntu-release-upgrader/release-upgrade-motd ]; then
    exec /usr/lib/ubuntu-release-upgrader/release-upgrade-motd
 fi

calls /usr/lib/ubuntu-release-upgrader/release-upgrade-motd:

 stamp=/var/lib/ubuntu-release-upgrader/release-upgrade-available
 if [ -f "$stamp" ]; then
	# Stamp exists, see if it's expired
	now=$(date +%s)
        lastrun=$(stat -c %Y "$stamp") 2>/dev/null || lastrun=0
        expiration=$(expr $lastrun + 86400)
        if [ $now -ge $expiration ]; then
		# Older than 1 day old, so update in the background
		/usr/lib/ubuntu-release-upgrader/check-new-release -q > "$stamp" &     # <--- Line 31
	elif [ -s "$stamp" ]; then
		# Less than 1 day old, and non-empty, so display now
		cat "$stamp"
		echo
	fi
 elif [ "$(id -u)" = 0 ]; then
	# No cache at all, so update in the background
	/usr/lib/ubuntu-release-upgrader/check-new-release -q > "$stamp" &
 fi


on 20.04 wsl:

 $stat -c '%A %a %n' /var/lib/ubuntu-release-upgrader/                                                    
 drwxr-xr-x 755 /var/lib/ubuntu-release-upgrader/

 $ ls -la /var/lib/ubuntu-release-upgrader
 drwxr-xr-x  2 root root 4096 Nov  8 13:31 .
                       
same on 16.04 wsl


I don't think /var/lib/ubuntu-release-upgrader/release-upgrade-available can be created because /var/lib/ubuntu-release-upgrader/ belongs to root.

This works fine in containers where users are privileged by default but
runs into an issue when WSL starts as an unprivileged user.

Users are not going to invoke motd with sudo normally and this error is
confusing to inexperienced users so it should be fixed.


/usr/lib/ubuntu-release-upgrader/release-upgrade-motd is in ubuntu-release-upgrader-core: https://git.launchpad.net/ubuntu/+source/ubuntu-release-upgrader/tree/debian/release-upgrade-motd?h=ubuntu/focal



** Also affects: update-motd
   Importance: Undecided
       Status: New

** Also affects: ubuntu-release-upgrader (Ubuntu)
   Importance: Undecided
       Status: New

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https://bugs.launchpad.net/bugs/1873545

Title:
  Permission denied error from show-motd when updates available

Status in Ubuntu WSL:
  New
Status in update-motd:
  New
Status in ubuntu-release-upgrader package in Ubuntu:
  New
Status in update-motd package in Ubuntu:
  New

Bug description:
  motd on demo of 20.04:

  Welcome to Ubuntu 20.04 LTS (GNU/Linux 4.19.84-microsoft-standard
  x86_64)

  ....

  26 updates can be installed immediately.
  0 of these updates are security updates.
  To see these additional updates run: apt list --upgradable

  /usr/lib/ubuntu-release-upgrader/release-upgrade-motd: 31: cannot
  create /var/lib/ubuntu-release-upgrader/release-upgrade-available:
  Permission denied

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