Some fixes for non woring sudo

README.md

@@ -83,6 +83,10 @@ If this command fails, configure the remote account's `sudoers` entry for the
 necessary `zfs` commands with `NOPASSWD` before running the migration. Do not
 put a password in the script or on its command line.
 
+`REMOTE_HOST` must be a complete hostname or address, such as
+`root@192.0.2.10` or `admin@new-server`. `root@` is invalid because it has no
+host after the `@`.
+
 Options:
 
 | Option | Description |

zfs-move-over-ssh.sh

@@ -83,14 +83,18 @@ REMOTE_HOST="$2"
 DESTINATION_ROOT="${3%/}"
 SNAPSHOT_NAME="move-$(date +%Y%m%d-%H%M%S)"
 
+[[ "$REMOTE_HOST" != *@ ]] || die "REMOTE_HOST is missing a hostname; use user@server-name or server-name"
+
 command -v zfs >/dev/null || die "zfs command was not found"
 command -v zpool >/dev/null || die "zpool command was not found"
 command -v ssh >/dev/null || die "ssh command was not found"
 zpool list -H -o name "$SOURCE_POOL" >/dev/null || die "source pool does not exist: $SOURCE_POOL"
 
 if ! $DRY_RUN; then
+    ssh "${SSH_OPTIONS[@]}" "$REMOTE_HOST" true \
+        || die "cannot authenticate to $REMOTE_HOST with SSH keys or an SSH agent"
     ssh "${SSH_OPTIONS[@]}" "$REMOTE_HOST" 'sudo -n zfs list -H -o name -t filesystem >/dev/null' \
-    || die "cannot connect with non-interactive SSH or run 'sudo -n zfs' on $REMOTE_HOST"
+        || die "$REMOTE_HOST accepts SSH, but cannot run 'sudo -n zfs'; configure passwordless sudo for zfs"
 fi
 
 map_destination() {