[Bug 1959047] Re: systemd ignores RootDirectory option in .service units

[Luca Boccassi]

Is there a chance to SRU a targeted patch for LXD in Bionic to fix the
issue instead?

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Title:
  systemd ignores RootDirectory option in .service units

Status in systemd package in Ubuntu:
  Confirmed

Bug description:
  The version of systemd (249.5-2ubuntu4) currently packaged for the
  Ubuntu development version (22.04 Jammy Jellyfish) totally ignores the
  RootDirectory= option in systemd service files. With RootDirectory,
  systemd should start the service after calling chroot() on the
  supplied directory.

  To test/reproduce, create a test service file with the following
  contents:

  
  # /etc/systemd/system/lsb-release.service
  [Unit]
  Description=LSB Release Information

  [Service]
  Type=simple
  RootDirectory=/var/chroot/trusty
  ExecStartPre=/bin/pwd
  ExecStart=/usr/bin/lsb_release -a

  
  You should have a chroot environment in the specified RootDirectory, even though you can still deduce if systemd attempted to chroot or not from the resulting error message.

  In my example, I installed an end-of-life Ubuntu 14.04 Trusty Tahr in
  the chroot environment. On systems NOT affected by the problem, I get
  the following result when I start this test service. This is what I'd
  expect.

  
  Jan 25 20:40:40 dolly systemd[1]: Starting LSB Release Information...
  Jan 25 20:40:40 dolly pwd[361]: /
  Jan 25 20:40:40 dolly systemd[1]: Started LSB Release Information.
  Jan 25 20:40:40 dolly lsb_release[362]: No LSB modules are available.
  Jan 25 20:40:40 dolly lsb_release[362]: Distributor ID:        Ubuntu
  Jan 25 20:40:40 dolly lsb_release[362]: Description:        Ubuntu 14.04 LTS
  Jan 25 20:40:40 dolly lsb_release[362]: Release:        14.04
  Jan 25 20:40:40 dolly lsb_release[362]: Codename:        trusty
  Jan 25 20:40:40 dolly systemd[1]: lsb-release.service: Succeeded.

  
  On the problematic system, however, I get the following result.

  
  Jan 25 21:21:08 savelog systemd[1]: Starting LSB Release Information...
  Jan 25 21:21:08 savelog systemd[1]: Started LSB Release Information.
  Jan 25 21:21:08 savelog pwd[81114]: /
  Jan 25 21:21:08 savelog lsb_release[81115]: No LSB modules are available.
  Jan 25 21:21:08 savelog lsb_release[81115]: Distributor ID:        Ubuntu
  Jan 25 21:21:08 savelog lsb_release[81115]: Description:        Ubuntu Jammy Jellyfish (development branch)
  Jan 25 21:21:08 savelog lsb_release[81115]: Release:        22.04
  Jan 25 21:21:08 savelog lsb_release[81115]: Codename:        jammy
  Jan 25 21:21:08 savelog systemd[1]: lsb-release.service: Deactivated successfully.

  
  It totally run the service on the host's root filesystem, it didn't care even the slightest that a RootDirectory is specified.

  Tested on the following releases / systemd versions:

  Ubuntu 18.04.6 Bionic Beaver – ISSUE NOT PRESENT
  systemd 237
  +PAM +AUDIT +SELINUX +IMA +APPARMOR +SMACK +SYSVINIT +UTMP +LIBCRYPTSETUP +GCRYPT +GNUTLS +ACL +XZ +LZ4 +SECCOMP +BLKID +ELFUTILS +KMOD -IDN2 +IDN -PCRE2 default-hierarchy=hybrid

  Ubuntu 20.04.3 Focal Fossa – ISSUE NOT PRESENT
  systemd 245 (245.4-4ubuntu3.15)
  +PAM +AUDIT +SELINUX +IMA +APPARMOR +SMACK +SYSVINIT +UTMP +LIBCRYPTSETUP +GCRYPT +GNUTLS +ACL +XZ +LZ4 +SECCOMP +BLKID +ELFUTILS +KMOD +IDN2 -IDN +PCRE2 default-hierarchy=hybrid

  Ubuntu 21.10 Impish Indri – ISSUE NOT PRESENT
  systemd 248 (248.3-1ubuntu8.2)
  +PAM +AUDIT +SELINUX +APPARMOR +IMA +SMACK +SECCOMP +GCRYPT +GNUTLS -OPENSSL +ACL +BLKID +CURL +ELFUTILS -FIDO2 +IDN2 -IDN +IPTC +KMOD +LIBCRYPTSETUP -LIBFDISK +PCRE2 -PWQUALITY -P11KIT -QRENCODE +BZIP2 +LZ4 +XZ +ZLIB +ZSTD -XKBCOMMON +UTMP +SYSVINIT default-hierarchy=unified

  Ubuntu 22.04 Jammy Jellyfish (development branch) – ISSUE PRESENT
  systemd 249 (249.5-2ubuntu4)
  +PAM +AUDIT +SELINUX +APPARMOR +IMA +SMACK +SECCOMP +GCRYPT +GNUTLS -OPENSSL +ACL +BLKID +CURL +ELFUTILS -FIDO2 +IDN2 -IDN +IPTC +KMOD +LIBCRYPTSETUP -LIBFDISK +PCRE2 -PWQUALITY -P11KIT -QRENCODE +BZIP2 +LZ4 +XZ +ZLIB +ZSTD -XKBCOMMON +UTMP +SYSVINIT default-hierarchy=unified

  
  Note that the problem is produced under an LXC container; since systemd detects virtualization, it might change how it behaves.

  It's either a bug or an intentional change I don't understand yet
  (i.e. the RootDirectory option has deprecated and is about to be
  replaced with something else, or there are additional conditions to be
  met before RootDirectory is considered), but I think in the latter
  case I should at least get a warning that there is a change in
  configuration. I imagine suddenly everyone's existing service units
  utilizing RootDirectory silently stop working without any information
  regarding why.

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