etc: Add environment option to run init.d/ashd silently.

[ashd.git] / doc / userplex.doc

userplex(1)
===========

NAME
----
userplex - User directory multiplexer for ashd(7)

SYNOPSIS
--------
*userplex* [*-hIs*] [*-g* 'GROUP'] [*-m* 'MIN-UID'] [*-d* 'PUBDIR'] ['PROGRAM' ['ARGS'...]]

DESCRIPTION
-----------

The *userplex* handler serves user-defined content by logging in as
the requested user and running a request handler on that user's
behalf, running as that user.

*userplex* is a persistent handler, as defined in *ashd*(7), and the
handlers it starts for individual users must also be persistent
handlers. The same request handler will be reused for each individual
user as long as it does not exit.

When handling a request, *userplex* strips off the leading part of the
rest string, up until the first slash, and treats the stripped-off
part as a user name. If the user name is found on the system and
matches the criteria specified by the command-line options (see
OPTIONS below), and a request handler is not already running for that
user, *userplex* starts a request handler logged in as the user in
question (see LOGIN below) .

If the user has an executable file named `~/.ashd/handler` in his home
directory, it will be started and used as the request handler for that
user. Otherwise, a default handler is used. If the 'PROGRAM' argument
was given to *userplex*, it will be started as the handler program
(searching the *PATH* environment variable if it contains no
slashes). 'ARGS' will be passed to it as command-line arguments. If
'PROGRAM' was not given, the *dirplex*(1) program will be started by
default, with 'PUBDIR' passed as its only command-line
argument. 'PUBDIR' defaults to `htpub` if no 'PROGRAM' was specified.

If 'PUBDIR' was given (either by being specified explicitly, or
implicitly if no 'PROGRAM' argument was given), it is checked for
existence. If it does not exist, *userplex* returns a 404 response to
the client.

If there exists a file named `~/.ashd/error` in the user's home
directory, it will be opened in append mode and connected to the
request handler's standard error. If it does not exist, `/dev/null`
will be opened and connected to standard error instead. In the same
manner, `~/.ashd/output` will be opened and connected to the request
handler's standard output if it exists.

OPTIONS
-------

*-h*::

	Print a brief help message to standard output and exit.

*-I*::

	If given, ignore any `~/.ashd/handler` file in a user's home
	directory and use only the default handler.

*-s*::

	If given, set the ASHD_USESYSLOG environment variable in all
	started children. If not given, *userplex* will actively clear
	the variable from its children instead. The presence of the
	variable indicates to the standard ashd programs to log
	messages to *syslog*(3) instead of printing them on standard
	error.

*-g* 'GROUP'::

	If given, only users that are members of the named 'GROUP'
	will be considered for serving. Requesting another user will
	return a 404 response to the client.

*-m* 'MIN-UID'::

	If given, only users that have a UID of at least 'MIN-UID'
	will be considered for serving. Requesting another user will
	return a 404 response to the client.

*-d* 'PUBDIR'::

	If given, 'PUBDIR' will be checked for existence before
	starting the default request handler for a requested user. If
	the 'PROGRAM' argument was not given to *userplex*, it will be
	passed as the single argument to *dirplex*(1), which is
	invoked by default. If neither the *-d* option nor the
	'PROGRAM' argument were given to *userplex*, 'PUBDIR'
	defaults to `htpub`.

LOGIN
-----

As part of the login procedure, *userplex* does the following:

 * A new session is entered (with *setsid*(2)).

 * The UID, GID and auxiliary groups of the new process are changed
   accordingly. For testing purposes, *userplex* may be running as a
   user other than root, and the child process will, then, simply exit
   if it is not running as the requested user.

 * The child process will change directory to the user's home
   directory.

 * The *HOME*, *SHELL*, *USER* and *LOGNAME* environment variables are
   set appropriately.

Note that no shell is actually spawned, and that no profile scripts or
similar will therefore be run. If it is important that your personal
environment variables are set properly, a useful trick is to install a
simple shell script as `~/.ashd/handler`, containing the following two
lines:

--------
#!/bin/sh -l
exec dirplex htpub
--------

The standard *-l* switch to the shell (see *sh*(1)) will make it run
its normal login procedure, and then *exec*(2) the *dirplex*(1)
handler to serve files normally. Of course, the second line can be
replaced by whatever other handler one might wish to use.

AUTHOR
------
Fredrik Tolf <fredrik@dolda2000.com>

SEE ALSO
--------
*dirplex*(1), *patplex*(1) (the EXAMPLES section), *ashd*(7)