Manually send SIGHUP to vtysh when the current session was disconnect…

…ed (sonic-net#1801)

* Manually send SIGHUP to vtysh when the current session was disconnected

* Address comments

dockers/docker-fpm-frr/base_image_files/vtysh

@@ -1,3 +1,16 @@
 #!/bin/bash
 
-docker exec -i bgp vtysh "$@"
+# Determine whether stdout is on a terminal
+if [ -t 1 ] ; then
+  # Prepare a function to send HUP signal to vtysh in the container
+  # we mark the new instance of vtysh with the current tty as a tag
+  TTY=$(tty)
+  function cleanup
+  {
+    docker exec -i bgp pkill -HUP -f "vtysh $TTY"
+  }
+  trap cleanup HUP
+  docker exec -ti bgp vtysh "$TTY" "$@"
+else
+  docker exec -i bgp vtysh "$@"
+fi

dockers/docker-fpm-quagga/base_image_files/vtysh

@@ -1,3 +1,16 @@
 #!/bin/bash
 
-docker exec -i bgp vtysh "$@"
+# Determine whether stdout is on a terminal
+if [ -t 1 ] ; then
+  # Prepare a function to send HUP signal to vtysh in the container
+  # we mark the new instance of vtysh with the current tty as a tag
+  TTY=$(tty)
+  function cleanup
+  {
+    docker exec -i bgp pkill -HUP -f "vtysh $TTY"
+  }
+  trap cleanup HUP
+  docker exec -ti bgp vtysh "$TTY" "$@"
+else
+  docker exec -i bgp vtysh "$@"
+fi