Systemd-259.1 for SysV

Configuring systemd

The /etc/pam.d/system-session file needs to be modified and a new file needs to be created in order for systemd-logind to work correctly. Run the following commands as the root user:

grep 'pam_systemd' /etc/pam.d/system-session ||
cat >> /etc/pam.d/system-session << "EOF"
# Begin Systemd addition

session  required    pam_loginuid.so
session  optional    pam_systemd.so

# End Systemd addition
EOF

cat > /etc/pam.d/systemd-user << "EOF"
# Begin /etc/pam.d/systemd-user

account  required    pam_access.so
account  include     system-account

session  required    pam_env.so
session  required    pam_limits.so
session  required    pam_loginuid.so
session  optional    pam_keyinit.so force revoke
session  optional    pam_systemd.so

auth     required    pam_deny.so
password required    pam_deny.so

# End /etc/pam.d/systemd-user
EOF

The “system” mode of systemd should now be restricted to only start a minimum set of daemons. As the root user:

rm -v /usr/lib/systemd/system-generators/*                 &&
grep -l systemctl      /usr/lib/udev/rules.d/* | \
    xargs sed -i '/systemctl/s/^/#/'                       &&
grep -l systemd-sysctl /usr/lib/udev/rules.d/* | \
    xargs sed -i '/systemd-sysctl/s/^/#/'                  &&
for t in sysinit.target basic.target; do
  sed -E '/^(Wants|After|Conflicts|Requires|Before)/s/^/#/' \
      /usr/lib/systemd/system/$t > /etc/systemd/system/$t
done                                                       &&
rm -rfv /usr/lib/systemd/system/sysinit.target.wants.ignore &&
mv  /usr/lib/systemd/system/sysinit.target.wants{,.ignore} &&
ln -sfv sysinit.target /etc/systemd/system/default.target   &&
mkdir -pv /etc/systemd/system/sysinit.target.wants         &&
for u in systemd-journal-catalog-update.service \
         systemd-journal-flush.service          \
         systemd-journald.service               \
         systemd-logind.service; do
  cp -v /usr/lib/systemd/system/$u /etc/systemd/system &&
  ln -sfv ../$u /etc/systemd/system/sysinit.target.wants
done                                                       &&
ln -sfv /dev/null      /etc/systemd/system/tmp.mount

Now the shutdown process of systemd has to be modified to interact nicely with SysV. This is done by introducing a unit that triggers a switch to runlevel 1 at the beginning of the systemd shutdown process and by replacing the systemd-shutdown executable with a small script. As the root user:

cat > /etc/systemd/system/telinit1.service << EOF &&
[Unit]
Description=trigger single user mode at shutdown
# Must trigger before shutting down dbus
After=dbus.service

[Service]
Type=oneshot
ExecStop=/usr/sbin/telinit 1
ExecStop=/usr/bin/sleep 1
RemainAfterExit=yes
EOF
ln -s ../telinit1.service /etc/systemd/system/sysinit.target.wants &&

mv /usr/lib/systemd/systemd-shutdown{,.orig} &&
cat > /usr/lib/systemd/systemd-shutdown <<"EOF" &&
#!/usr/bin/bash

while [ -n "$1" ]; do
   case "$1" in
      --*) shift; continue ;;
      reboot|poweroff|halt|kexec|exit) cmd="$1"; break ;;
      *) echo Unrecognized option: $1; exit 1 ;;
   esac
done
if [ -z "$cmd" ]; then echo No command given; exit 1; fi
if [ reboot = "$cmd" ]; then telinit 6
                        else telinit 0
fi
EOF
chmod a+x /usr/lib/systemd/systemd-shutdown

install -vdm755 /etc/systemd/user-environment-generators &&
cat > /etc/systemd/user-environment-generators/50-profile.sh << "EOF" &&
#!/usr/bin/env -S -i /usr/bin/bash
# SPDX-License-Identifier: MIT

. /etc/profile

# Systemd should have already set a better value for them.
unset XDG_RUNTIME_DIR
for i in $(locale); do
  unset ${i%=*}
done

# Some shell magic that we don't want to expose.
unset SHLVL

# Systemd does not want to pass functions to the environment
for i in $(declare -pF | awk '{print $3}'); do
  unset -f $i
done

python3 << _EOF
import os
for var in os.environ:
  # Simply unsetting them in shell does not work.
  if var in ['LC_CTYPE', '_']:
    continue

  print(var + '=' + os.environ[var])
_EOF
EOF

chmod -v 755 /etc/systemd/user-environment-generators/50-profile.sh

make install-systemd