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<title>User service daemon and client specification - Information passed through the client/daemon combination</title>
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<h1>
-User service daemon and client specification - chapter 5<br>
-Information passed through the client/daemon combination
+User service daemon and client specification
+<br>Chapter 5 - Information passed through the client/daemon combination
</h1>
-The information described below is the only information which passes
-between the caller and the service.
+<hr>
+
+
+<p>
+The information described below is the only information which passes between
+the caller and the service.
<ul>
-<li>The service name supplied by the caller is available in the
-configuration language for deciding whether and which service program
-to invoke, in the <kbd>service</kbd> parameter, and is used by the
-<kbd>execute-from-directory</kbd> and <kbd>execute-from-path</kbd>
-configuration directives. It is usually used to select which service
-program to invoke. It is also passed to the service program in the
-<kbd>USERV_SERVICE</kbd> environment variable.
-<p><li>File descriptors specified by the client and allowed according to the
-configuration language will be connected. Each file descriptor is
-opened for reading or writing. Communication is via pipes, one end of
-each pipe being open on the appropriate file descriptor in the service
-program (when it is invoked) and the other end being held by the
-client process, which will read and write files it opens on behalf of
-its caller or file descriptors it is passed by its caller.<P>
-
-Data may be passed into the service through reading pipes and out of
-it through writing pipes. These pipes can remain open only until the
-service and client have terminated, or can be made to stay open after
-the client has terminated and (if the service program forks) the main
-service process has exited; the behaviour is controlled by options
-passed to the client by its caller.<P>
-
-The caller can arrange that a writing pipe be connected to a pipe or
-similar object and cause attempts to write to that descriptor by the
-service to generate a <kbd>SIGPIPE</kbd> (or <kbd>EPIPE</kbd> if
-<kbd>SIGPIPE</kbd> is caught or ignored) in the service.<P>
-
-Likewise, the service can close filedescriptors specified for reading,
-which will cause the corresponding filedescriptors passed by the
-caller to be closed, so that if these are pipes processes which write
-to them will receive <kbd>SIGPIPE</kbd> or <kbd>EPIPE</kbd>.
-<p><li>If <kbd>no-suppress-args</kbd> is set then arguments passed to the client
-by its caller will be passed on, verbatim, to the service.
-<p><li>Fatal signals and system call failures experienced by the client will
-result in the disconnection of the service from the client and
-possibly some of the communication file descriptors described above;
-if <kbd>disconnect-hup</kbd> is set then the service will also be sent a
-<kbd>SIGHUP</kbd>.
-<p><li>The value of the <kbd>LOGNAME</kbd> (or <kbd>USER</kbd>) environment variable
-as passed to the client will be used as the login name of the calling
-user if the uid of the calling process matches the uid corresponding
-to that login name. Otherwise the calling uid's password entry will
-be used to determine the calling user's login name.<P>
-
-This login name and the calling uid are available in the configuration
-language in the <kbd>calling-user</kbd> parameter and are passed to the
-service program in environment variables <kbd>USERV_USER</kbd> and
-<kbd>USERV_UID</kbd>.<P>
-
-The shell corresponding to that login name (according to the password
-entry) is available as in the configuration language's
-<kbd>calling-user-shell</kbd> parameter.<P>
-
-If no relevant password entry can be found then no service will be
-invoked.
-<p><li>The numeric values and textual names for calling gid and supplementary
-group list are available in the configuration language in the
-<kbd>calling-group</kbd> parameter and are passed to the service in
-environment variables.<P>
-
-If no name can be found for a numeric group to which the calling
-process belongs then no service will be invoked.
-<p><li>The name of the current working directory in which the client was
-invoked is passed, if available and not hidden using <kbd>--hidecwd</kbd>,
-to the service program in the <kbd>USERV_CWD</kbd> variable. This grants no
-special access to that directory unless it is a subdirectory of a
-directory which is executable (searchable) but not readable by the
-service user.
-<p><li>Settings specified by the caller using the <code>--defvar
-</code><var>name</var><code>=</code><var>value</var><code></code> option to the client are available in the
-configuration language as the corresponding <code>u-</code><var>name</var><code></code>
-parameters and are passed to the service program in environment
-variables <code>USERV_U_</code><var>name</var><code></code>.
-<p><li>If the calling user is root or the same as the service user then
-options may be given to the client which bypass the usual security
-features; in this case other information may pass between the caller
-and the service.
-<p></ul>
+<li>
+The service name supplied by the caller is available in the configuration
+language for deciding whether and which service program to invoke, in the
+<code>service</code> parameter, and is used by the
+<code>execute-from-directory</code> and <code>execute-from-path</code>
+configuration directives. It is usually used to select which service program
+to invoke. It is also passed to the service program in the
+<code>USERV_SERVICE</code> environment variable.
+</li>
+</ul>
+<ul>
+<li>
+File descriptors specified by the client and allowed according to the
+configuration language will be connected. Each file descriptor is opened for
+reading or writing. Communication is via pipes, one end of each pipe being
+open on the appropriate file descriptor in the service program (when it is
+invoked) and the other end being held by the client process, which will read
+and write files it opens on behalf of its caller or file descriptors it is
+passed by its caller.
+
+<p>
+Data may be passed into the service through reading pipes and out of it through
+writing pipes. These pipes can remain open only until the service and client
+have terminated, or can be made to stay open after the client has terminated
+and (if the service program forks) the main service process has exited; the
+behaviour is controlled by options passed to the client by its caller.
+
+<p>
+The caller can arrange that a writing pipe be connected to a pipe or similar
+object and cause attempts to write to that descriptor by the service to
+generate a <code>SIGPIPE</code> (or <code>EPIPE</code> if <code>SIGPIPE</code>
+is caught or ignored) in the service.
+
+<p>
+Likewise, the service can close filedescriptors specified for reading, which
+will cause the corresponding filedescriptors passed by the caller to be closed,
+so that if these are pipes processes which write to them will receive
+<code>SIGPIPE</code> or <code>EPIPE</code>.
+</li>
+</ul>
+<ul>
+<li>
+If <code>no-suppress-args</code> is set then arguments passed to the client by
+its caller will be passed on, verbatim, to the service.
+</li>
+</ul>
+<ul>
+<li>
+Fatal signals and system call failures experienced by the client will result in
+the disconnection of the service from the client and possibly some of the
+communication file descriptors described above; if <code>disconnect-hup</code>
+is set then the service will also be sent a <code>SIGHUP</code>.
+</li>
+</ul>
+<ul>
+<li>
+The value of the <code>LOGNAME</code> (or <code>USER</code>) environment
+variable as passed to the client will be used as the login name of the calling
+user if the uid of the calling process matches the uid corresponding to that
+login name. Otherwise the calling uid's password entry will be used to
+determine the calling user's login name.
+
+<p>
+This login name and the calling uid are available in the configuration language
+in the <code>calling-user</code> parameter and are passed to the service
+program in environment variables <code>USERV_USER</code> and
+<code>USERV_UID</code>.
+
+<p>
+The shell corresponding to that login name (according to the password entry) is
+available as in the configuration language's <code>calling-user-shell</code>
+parameter.
+
+<p>
+If no relevant password entry can be found then no service will be invoked.
+</li>
+</ul>
+<ul>
+<li>
+The numeric values and textual names for calling gid and supplementary group
+list are available in the configuration language in the
+<code>calling-group</code> parameter and are passed to the service in
+environment variables.
+
+<p>
+If no name can be found for a numeric group to which the calling process
+belongs then no service will be invoked.
+</li>
+</ul>
+<ul>
+<li>
+The name of the current working directory in which the client was invoked is
+passed, if available and not hidden using <code>--hidecwd</code>, to the
+service program in the <code>USERV_CWD</code> variable. This grants no special
+access to that directory unless it is a subdirectory of a directory which is
+executable (searchable) but not readable by the service user.
+</li>
+</ul>
+<ul>
+<li>
+Settings specified by the caller using the <samp>--defvar
+<var>name</var>=<var>value</var></samp> option to the client are available in
+the configuration language as the corresponding <samp>u-<var>name</var></samp>
+parameters and are passed to the service program in environment variables
+<samp>USERV_U_<var>name</var></samp>.
+</li>
+</ul>
+<ul>
+<li>
+If the calling user is root or the same as the service user then options may be
+given to the client which bypass the usual security features; in this case
+other information may pass between the caller and the service.
+</li>
+</ul>
<hr>
+
+[ <a href="ch-config.html">previous</a> ]
+[ <a href="index.html#contents">Contents</a> ]
+[ <a href="ch-intro.html">1</a> ]
+[ <a href="ch-client.html">2</a> ]
+[ <a href="ch-envir.html">3</a> ]
+[ <a href="ch-config.html">4</a> ]
+[ 5 ]
+[ <a href="ch-notes.html">6</a> ]
+[ <a href="ch-notes.html">next</a> ]
+
+<hr>
+
+<p>
User service daemon and client specification
-- <A href="index.html#copyright"><kbd>userv</kbd> is Copyright 1996-1999 Ian Jackson.</A>
-<br>
-<A href="index.html#toc">Contents</A>; <A href="index.html#abstract">abstract</A>; <A href="ch-notes.html">next</A>; <A href="ch-config.html">back</A>.
-<br>
-<address>0.61.4<br>
-Ian Jackson <A href="mailto:ian@davenant.greenend.org.uk">ian@davenant.greenend.org.uk</A></address>
-</body></html>
+
+<address>
+1.0.3<br>
+Ian Jackson <code><a href="mailto:ian@davenant.greenend.org.uk">ian@davenant.greenend.org.uk</a></code>
+</address>
+
+<hr>
+
+</body>
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+</html>
+
~ian / userv.git / blobdiff