* Prevent set -u from falling over unset SSH_CONNECTION variable

[code/molly-guard.git] / shutdown

diff --git a/shutdown b/shutdown
index 0a6efd6011e590fea9ef6e80dc6ae0c2ce48fe37..0c52d92803e65b8e7615b918e9910e7ea55102b6 100755 (executable)
--- a/shutdown
+++ b/shutdown
@@ -9,31 +9,121 @@
 #
 set -eu
 
+ME=molly-guard
+
 CMD="${0##*/}"
 EXEC="/sbin/$CMD"
+
 case "$CMD" in
-  halt|reboot|shutdown)
+  halt|reboot|shutdown|poweroff)
+    if [ ! -f $EXEC ]; then
+      echo "E: $ME: not a regular file: $EXEC" >&2
+      exit 4
+    fi
     if [ ! -x $EXEC ]; then
-      echo "E: not an executable: $EXEC" >&2
+      echo "E: $ME: not an executable: $EXEC" >&2
       exit 3
     fi
     ;;
   *)
-    echo "E: unsupported command: $CMD" >&2
+    echo "E: $ME: unsupported command: $CMD" >&2
     exit 1
     ;;
 esac
 
-if [ -n "${SSH_CONNECTION:-}" ] && test -t 0 && [ "${1:-}" != '--help' ]; then
-  echo -n "SSH session detected, type in hostname of the machine to $CMD: "
-  read HOSTNAME_USER
+usage()
+{
+  cat <<-_eousage
+       Usage: $ME [options]
+              (shielding $EXEC)
+
+       Instead of invoking $EXEC directly, $ME will prompt the user for the
+       machine's hostname to guard against accidental shutdowns/reboots, if the
+       current shell is a child of an SSH connection (or --pretend-ssh) has been
+       given on the command line, if the shell is connected to an interactive
+       terminal, and the actual command to execute is does not involve --help or is
+       \`shutdown -c'.
+
+       Only if the user enters the machine's hostname correctly will $ME take
+       action. Specifying --molly-guard-do-nothing as argument to the command will
+       make $ME echo the command it would execute rather than actually executing
+       it.
+
+       The actual command's help output follows:
 
-  HOSTNAME="$(hostname)"
+       _eousage
+}
 
-  if [ "$HOSTNAME_USER" != "$HOSTNAME" ]; then
-    echo "Good thing I asked; I won't $CMD $HOSTNAME ..."
-    exit 2
+ARGS=
+DO_NOTHING=0
+PRETEND_SSH=0
+for arg in "$@"; do
+  case "$arg" in
+    (*-molly-guard-do-nothing) DO_NOTHING=1;;
+    (*-help)
+      usage 2>&1
+      eval $EXEC --help 2>&1
+      exit 0
+      ;;
+    (*-pretend-ssh) PRETEND_SSH=1;;
+    *) ARGS="${ARGS:+$ARGS }$arg";;
+  esac
+done
+
+do_real_cmd()
+{
+  if [ $DO_NOTHING -eq 1 ]; then
+    echo "$ME: would run: $EXEC $ARGS"
+    exit 0
+  else
+    eval exec $EXEC "$ARGS"
   fi
+}
+
+if [ $DO_NOTHING -eq 1 ]; then
+  echo "I: demo mode; $ME will not do anything due to --molly-guard-do-nothing."
 fi
 
-exec $EXEC "$@"
+# require an interactive terminal connected to stdin
+test -t 0                    || do_real_cmd
+
+# only run if we are being called over SSH, that is if the current terminal
+# was created by sshd.
+PTS=$(readlink /proc/$$/fd/0)
+if ! pgrep -f "^sshd.+${PTS#/dev/}[[:space:]]*$" >/dev/null \
+  && [ -z "${SSH_CONNECTION:-}" ]; then
+    if [ $PRETEND_SSH -eq 1 ]; then
+      echo "I: this is not an SSH session, but --pretend-ssh was given..."
+    else
+      do_real_cmd
+    fi
+else
+  echo "W: $ME: SSH session detected!"
+fi
+
+# pass through certain commands
+case "$CMD $ARGS" in
+  (*shutdown\ *-c*) 
+    echo "I: executing $CMD $ARGS regardless of SSH session."
+    do_real_cmd
+    ;;
+esac
+
+HOSTNAME="$(hostname --short)"
+
+sigh()
+{
+  echo "Good thing I asked; I won't $CMD $HOSTNAME ..."
+  exit 2
+}
+
+trap 'echo;sigh' 1 2 3 9 10 12 15
+
+echo -n "Please type in hostname of the machine to $CMD: "
+read HOSTNAME_USER || :
+
+[ "$HOSTNAME_USER" = "$HOSTNAME" ] || sigh
+
+trap - 1 2 3 9 10 12 15
+
+do_real_cmd