consequence of not using risky_shell

[Magnus Fröberg]

Hi

well I didn't comment on the original "risky_shell" mail
discussion but, uhh, removing the old shell behaviour really
makes it a hard time debugging bad (maybe hanging) startup
sequenses in especially highly distributed environments.

I would recommend not making this flag an undocumented feature
as it is really needed.
Actually, I think the default behaviour should be the old
in an interactive system at least.

We'll always start our system nodes with this flag enabled!

/Magnus


Ulf Wiger (AL/EAB) wrote:
> Not that I want to gripe too much about the change in the 
> shell behaviour -- that it doesn't become available before the 
> boot sequence is finished... 
> 
> (see http://www.erlang.org/ml-archive/erlang-questions/200412/msg00045.html and follow-ups)
> 
> but the following situation was a bit annoying:
> 
> 
> =PROGRESS REPORT==== 11-Feb-2005::15:47:21 ===
>          application: mnesia
>           started_at: nonode@REDACTED
> will wait for tables (time: {15,47,21})
> 
> User switch command
>  --> l
> Unknown command
>  --> h
>   c [nn]   - connect to job
>   i [nn]   - interrupt job
>   k [nn]   - kill job
>   j        - list all jobs
>   s        - start local shell
>   r [node] - start remote shell
>   q        - quit erlang
>   ? | h    - this message
>  --> s
>  --> c
> 
> User switch command
>  --> j
>    1  {shell,start,[]}
>    2* {shell,start,[]}
> 
> 
> One application in my boot sequence called mnesia:wait_for_tables(Tabs, infinity). Some table doesn't load for some reason, and since the shell doesn't become available until after the completed boot sequence, I had a hard time debugging it. Eventually, I managed to re-install the system, reproduce the error and use rpc:call(...,mnesia,info,[]) from another erlang node.
> 
> Using Ctrl-G and spawning a new shell doesn't help; the new shell will also hang. Also, starting a remote shell using Ctrl-G from another node fails in the same fashion.
> 
> The problem? I had forgotten to call application:load(mnesia) before running my function that created a schema, started mnesia, and created the tables (or rather, the install() function should have done this too). As a result, the environment variable telling mnesia where to create the schema wasn't initialized, and the disc_only tables weren't created.
> 
> It feels like some debugging aide is missing now that there is no shell prompt during boot. Perhaps one should be allowed to start a shell using Ctrl-G even though the main shell isn't finished?
> 
> /Uffe


-- 
Magnus Fröberg                   Tel: +46 (0)8 545 55 026
Alteon WebSystems AB             Email: mfroberg@REDACTED
Sveavägen 151, P.O. Box 6701     WWW: http://www.alteonwebsystems.com
SE-113 85 Stockholm, SWEDEN