[Bug 2075546] Re: Cannot install into target '/tmp/ubuntu-image-XXX/chroot' mounted with noexec or nodev

[Paul Mars]

I see several ways to solve/prevent from this:
- force users setting a workdir (not a great solution I think because it will break existing workflows)
- try to detect if the workdir we selected is unfit to build the image and properly stop the build to inform the user. This way it will keep working on older systems and will force users on newer ones to set a workdir.
- use another default workdir to build the image. Aside from the current working dir I do not see any great candidate we could rely on but maybe I am missing some.

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Title:
  Cannot install into target '/tmp/ubuntu-image-XXX/chroot' mounted with
  noexec or nodev

Status in Ubuntu Image:
  New

Bug description:
  On a fresh oracular installation /tmp is a tmpfs mounted by systemd
  tmp.mount which is mounted with nodev permissions. This leads to the
  following error when trying to run ubuntu-image:

  [0] prepare_gadget_tree                                                                                                                                                                                              
  [1] load_gadget_yaml                                                                                                                                                                                                 
  [2] verify_artifact_names                                                                                                                                                                                            
  [3] germinate                                                                                                                                                                                                        
  [4] create_chroot                                                                                                                                                                                                    
  Error: Error running debootstrap command "/snap/ubuntu-image/876/usr/sbin/debootstrap --arch arm64 --variant=minbase --include=ca-certificates --components=main,universe,multiverse,restricted oracular /tmp/ubuntu-
  image-100185c6-1f8d-4d44-88e8-20fa8b330c1e/chroot http://ports.ubuntu.com/ubuntu-ports/". Error is "exit status 1". Output is: 
  /snap/ubuntu-image/876/usr/sbin/debootstrap: 1638: cannot create /tmp/ubuntu-image-100185c6-1f8d-4d44-88e8-20fa8b330c1e/chroot/test-dev-null: Permission denied
  E: Cannot install into target '/tmp/ubuntu-image-100185c6-1f8d-4d44-88e8-20fa8b330c1e/chroot' mounted with noexec or nodev

  Looking at mount this is confirmed:

  $ mount | grep /tmp
  tmpfs on /tmp type tmpfs (rw,nosuid,nodev,nr_inodes=1048576,inode64)

  The offender is the systemd tmp.mount target:

  $ systemctl cat tmp.mount
  # /usr/lib/systemd/system/tmp.mount
  #  SPDX-License-Identifier: LGPL-2.1-or-later
  #
  #  This file is part of systemd.
  #
  #  systemd is free software; you can redistribute it and/or modify it
  #  under the terms of the GNU Lesser General Public License as published by
  #  the Free Software Foundation; either version 2.1 of the License, or
  #  (at your option) any later version.

  [Unit]
  Description=Temporary Directory /tmp
  Documentation=https://systemd.io/TEMPORARY_DIRECTORIES
  Documentation=man:file-hierarchy(7)
  Documentation=https://systemd.io/API_FILE_SYSTEMS
  ConditionPathIsSymbolicLink=!/tmp
  DefaultDependencies=no
  Conflicts=umount.target
  Before=local-fs.target umount.target
  After=swap.target

  [Mount]
  What=tmpfs
  Where=/tmp
  Type=tmpfs
  Options=mode=1777,strictatime,nosuid,nodev,size=50%%,nr_inodes=1m

  Which is part of the systemd package in oracular:

  $ dpkg -S /usr/lib/systemd/system/tmp.mount
  systemd: /usr/lib/systemd/system/tmp.mount

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