units: simplify rescue.service and emergency.service (#5623)

The emergency.service and rescue.service units have become rather
convoluted. We spawn multiple shells and the help text spans multiple lines
which makes the units hard to read.

Move the logic into a single shell script and call that via ExecStart.

Makefile.am

@@ -443,6 +443,12 @@ userenvgenerator_PROGRAMS = \
 	30-systemd-environment-d-generator
 endif
 
+rootlibexec_SCRIPTS = \
+	src/sulogin-shell/systemd-sulogin-shell
+
+EXTRA_DIST += \
+	src/sulogin-shell/systemd-sulogin-shell.in
+
 dist_bashcompletion_data = \
 	shell-completion/bash/busctl \
 	shell-completion/bash/journalctl \
@@ -6329,6 +6335,10 @@ src/core/%.systemd: src/core/%.systemd.in
 src/%.policy.in: src/%.policy.in.in
 	$(SED_PROCESS)
 
+src/sulogin-shell/%: src/sulogin-shell/%.in
+	$(SED_PROCESS)
+	$(AM_V_GEN)chmod +x $@
+
 shell-completion/%: shell-completion/%.in
 	$(SED_PROCESS)
 

src/sulogin-shell/.gitignore

@@ -0,0 +1 @@
+systemd-sulogin-shell

src/sulogin-shell/systemd-sulogin-shell.in

@@ -0,0 +1,14 @@
+#!/bin/sh
+
+if [ -x /bin/plymouth ]; then
+    /bin/plymouth --wait quit
+fi
+
+cat <<EOF
+You are in $1 mode. After logging in, type "journalctl -xb" to view
+system logs, "systemctl reboot" to reboot, "systemctl default" or ^D to
+boot into default mode.
+EOF
+
+@SULOGIN@
+@SYSTEMCTL@ --job-mode=fail --no-block default

units/emergency.service.in

@@ -17,9 +17,7 @@ Before=shutdown.target
 [Service]
 Environment=HOME=/root
 WorkingDirectory=-/root
-ExecStartPre=-/bin/sh -c "[ -x /bin/plymouth ] && /bin/plymouth --wait quit"
-ExecStartPre=-/bin/echo -e 'You are in emergency mode. After logging in, type "journalctl -xb" to view\\nsystem logs, "systemctl reboot" to reboot, "systemctl default" or ^D to\\ntry again to boot into default mode.'
-ExecStart=-/bin/sh -c "@SULOGIN@; @SYSTEMCTL@ --job-mode=fail --no-block default"
+ExecStart=-@rootlibexecdir@/systemd-sulogin-shell emergency
 Type=idle
 StandardInput=tty-force
 StandardOutput=inherit

units/rescue.service.in

@@ -16,9 +16,7 @@ Before=shutdown.target
 [Service]
 Environment=HOME=/root
 WorkingDirectory=-/root
-ExecStartPre=-/bin/sh -c "[ -x /bin/plymouth ] && /bin/plymouth --wait quit"
-ExecStartPre=-/bin/echo -e 'You are in rescue mode. After logging in, type "journalctl -xb" to view\\nsystem logs, "systemctl reboot" to reboot, "systemctl default" or ^D to\\nboot into default mode.'
-ExecStart=-/bin/sh -c "@SULOGIN@; @SYSTEMCTL@ --job-mode=fail --no-block default"
+ExecStart=-@rootlibexecdir@/systemd-sulogin-shell rescue
 Type=idle
 StandardInput=tty-force
 StandardOutput=inherit