UNIX domain socket hanging around when not closed

UNIX domain socket hanging around when not closed

[Jan Hudec]

Hello,

I have a (possibly stupid) question. Is it OK, that dentries created by
binding unix-domain sockets remain in filesystem?

What I do is create a unix socket in /tmp and wait for clients to
connect in. The program removes the socket dentry when it shuts down,
but it sometimes crashes and the socket remains there.

Is there some reason the socket should remain unless explicitely
removed?

-------------------------------------------------------------------------------
						 Jan 'Bulb' Hudec <bulb@ucw.cz>

Re: UNIX domain socket hanging around when not closed

[Matti Aarnio]

On Wed, Aug 07, 2002 at 05:32:51PM +0200, Jan Hudec wrote:
> Hello,
> 
> I have a (possibly stupid) question. Is it OK, that dentries created by
> binding unix-domain sockets remain in filesystem?

   That is the classical behaviour, possibly because of tradition
   where they relate to named pipes created with mknod(1) command.

     http://www.ecst.csuchico.edu/~beej/guide/ipc/usock.html

> What I do is create a unix socket in /tmp and wait for clients to
> connect in. The program removes the socket dentry when it shuts down,
> but it sometimes crashes and the socket remains there.
> 
> Is there some reason the socket should remain unless explicitely
> removed?

   Traditional is also to   unlink() the socket name just prior
   to bind(3):ing it just in case there is a left-over entity
   with that name.


   The object name (it is NAMED entity, after all) space is
   filesystem name space.   I don't see any reason why not:

      - There could pre-exist the named socket (at a R/O
        filesystem), and no new name needs to be allocated
        in the filesystem for it.

      - The entire named entity would not be allowed to
        exist purely in VFS space, that is: creation wise
        the permission verification could ignore location
        directory being on a read/only file system, and
        just use directory permissions.  (Questions about
        memory expenditure, etc.  all kinds of trade-offs.)

  What the new POSIX writes about the issue, that I haven't
  yet looked into.

> 			 Jan 'Bulb' Hudec <bulb@ucw.cz>

/Matti Aarnio

Re: UNIX domain socket hanging around when not closed

[Alan Cox]

On Wed, 2002-08-07 at 16:32, Jan Hudec wrote:
> What I do is create a unix socket in /tmp and wait for clients to
> connect in. The program removes the socket dentry when it shuts down,
> but it sometimes crashes and the socket remains there.
> 
> Is there some reason the socket should remain unless explicitely
> removed?

Thats what is supposed to happen. If its dead then in your server you
can remove it and create a new one. 

Re: UNIX domain socket hanging around when not closed

[Alan Cox]

On Wed, 2002-08-07 at 16:56, Matti Aarnio wrote:
>       - There could pre-exist the named socket (at a R/O
>         filesystem), and no new name needs to be allocated
>         in the filesystem for it.
> 
>       - The entire named entity would not be allowed to
>         exist purely in VFS space, that is: creation wise
>         the permission verification could ignore location
>         directory being on a read/only file system, and
>         just use directory permissions.  (Questions about
>         memory expenditure, etc.  all kinds of trade-offs.)

Linux has a non file system name space for AF_UNIX sockets too. But its
a Linux extension