Added support for docker run --init

If you use this parameter to start your container, dumb-init is not used
at all. This deprecates the use of dumb-init, which in turn might be
removed some time in the future.

Also cleaned up some examples in the README.

Author: robinsmidsrod

README.md

@@ -18,7 +18,7 @@ How to use
 
 The most common use-case is to provide DHCP service to the host network of
 the machine running Docker.  For that you need to create a configuration for
-the DHCP server, start the container with the `--net=host` docker run
+the DHCP server, start the container with the `--net host` docker run
 option and specify the network interface you want to provide DHCP service
 on.
 
@@ -27,7 +27,7 @@ on.
     network interface.  If you need assistance, you can run
     `docker run -it --rm networkboot/dhcpd man dhcpd.conf` for a description
     of the configuration file syntax.
- 3. Run `docker run -it --rm --net=host -v "$(pwd)/data":/data networkboot/dhcpd eth0`.
+ 3. Run `docker run -it --rm --init --net host -v "$(pwd)/data":/data networkboot/dhcpd eth0`.
     `dhcpd` will automatically start and display its logs on the console.
     You can press Ctrl-C to terminate the server.
 
@@ -42,7 +42,7 @@ server as the same user that owns the `data` folder.  This ensures that the
 permissions on the files inside the `data` folder is kept consistent.  If
 the `data` folder is owned by root, dhcpd is run as the normal dhcpd user.
 
-If you forget to run the docker container with the `--net=host` option a
+If you forget to run the docker container with the `--net host` option a
 warning will be emitted informing you that you've probably forgotten it.
 
 If a `/data` volume is not provided with a `dhcpd.conf` inside it, the

run

@@ -1,5 +1,5 @@
 #!/bin/bash
 pushd $(dirname $0) >/dev/null
 data_dir="$(pwd)/data"
-docker run -ti --rm --net host -v "$data_dir":/data networkboot/dhcpd "$@"
+docker run -ti --rm --init --net host -v "$data_dir":/data networkboot/dhcpd "$@"
 popd >/dev/null

util/entrypoint.sh

@@ -3,7 +3,13 @@
 set -e
 
 
-init="/usr/bin/dumb-init"
+# Support docker run --init parameter which obsoletes the use of dumb-init,
+# but support dumb-init for those that still use it without --init
+if [ -x "/dev/init" ]; then
+    run="exec"
+else
+    run="exec /usr/bin/dumb-init --"
+fi
 
 # Single argument to command line is interface name
 if [ $# -eq 1 -a -n "$1" ]; then
@@ -63,8 +69,8 @@ if [ -n "$IFACE" ]; then
         echo "You must add the 'docker run' option '--net=host' if you want to provide DHCP service to the host network."
     fi
 
-    exec $init -- /usr/sbin/dhcpd -4 -f -d --no-pid -cf "$data_dir/dhcpd.conf" -lf "$data_dir/dhcpd.leases" $IFACE
+    $run /usr/sbin/dhcpd -4 -f -d --no-pid -cf "$data_dir/dhcpd.conf" -lf "$data_dir/dhcpd.leases" $IFACE
 else
     # Run another binary
-    exec $init -- "$@"
+    $run "$@"
 fi