doc: add mention of cloud-boothook to documentation

1 files changed, 12 insertions, 0 deletions

diff --git a/doc/userdata.txt b/doc/userdata.txt
index a1873424..00c16b25 100644
--- a/doc/userdata.txt
+++ b/doc/userdata.txt
@@ -48,6 +48,18 @@ finds.  However, certain types of user-data are handled specially.
    Content is placed into a file in /etc/init, and will be consumed
    by upstart as any other upstart job.
 
+ * Cloud Boothook 
+   begins with #cloud-boothook or Content-Type: text/cloud-boothook
+
+   This content is "boothook" data.  It is stored in a file under
+   /var/lib/cloud and then executed immediately.
+
+   This is the earliest "hook" available.  Note, that there is no
+   mechanism provided for running only once.  The boothook must take
+   care of this itself.  It is provided with the instance id in the
+   environment variable "INSTANCE_ID".  This could be made use of to
+   provide a 'once-per-instance'
+
 === Examples ===
 There are examples in the examples subdirectory.
 Additionally, the 'tools' directory contains 'write-mime-multipart',