doc/mgr/crash.rst: remove outdated module enabling instructions

The crash module has been enabled by default since commit 18f253aa in
Nautilus and is now in the always_on_modules list. However, the
documentation still contained instructions for manually enabling it.

When users followed these outdated instructions, they encountered:
```
  module 'crash' is already enabled (always-on)
```

The module cannot be disabled either. Running:
```
  ceph mgr module disable crash
```

Returns the error:
```
  Error EINVAL: module 'crash' cannot be disabled (always-on)
```
In this change, we remove the obsolete enabling instructions and clarify
that this module is always active and cannot be disabled.

Signed-off-by: Kefu Chai <tchaikov@gmail.com>
(cherry picked from commit 0fcd7677586f7edf3eb091420a8ace0c4f887167)

diff --git a/doc/mgr/crash.rst b/doc/mgr/crash.rst
index e7dab9d7c6794d8d6db5c30e5f73f9fc3515b24d..e0706337f186181ed4ba8dcd22e6cf4d5345c3a8 100644 (file)
--- a/doc/mgr/crash.rst
+++ b/doc/mgr/crash.rst
@@ -1,16 +1,15 @@
 Crash Module
 ============
+
 The crash module collects information about daemon crashdumps and stores
 it in the Ceph cluster for later analysis.
 
-Enabling
---------
-
-Enable the *crash* module by running the following command:
-
-.. prompt:: bash #
+Authentication Setup
+--------------------
 
-   ceph mgr module enable crash
+The *crash* module is one of the modules which are always on and cannot be
+disabled. To enable crash report archiving, you must first generate a keyring
+with appropriate privileges.
 
 Generate the *crash* upload key by running the following command:
 
@@ -18,15 +17,15 @@ Generate the *crash* upload key by running the following command:
 
    ceph auth get-or-create client.crash mon 'profile crash' mgr 'profile crash'
 
-On each node, you should store this key in
-``/etc/ceph/ceph.client.crash.keyring``.
+Store this key in ``/etc/ceph/ceph.client.crash.keyring`` on each node in your
+cluster.
 
 
 Automated collection
 --------------------
 
 Daemon crashdumps are dumped in ``/var/lib/ceph/crash`` by default; this can
-be configured with the option 'crash dir'.  Crash directories are named by
+be configured with the option ``crash dir``.  Crash directories are named by
 time and date and a randomly-generated UUID, and contain a metadata file
 'meta' and a recent log file, with a "crash_id" that is the same.