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| author | Laurent Bercot <ska-skaware@skarnet.org> | 2019-04-26 15:52:54 +0000 |
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| committer | Laurent Bercot <ska-skaware@skarnet.org> | 2019-04-26 15:52:54 +0000 |
| commit | 1bfba3b0be32306b078f5ee527b864e758b2c77b (patch) | |
| tree | 155db6f3c01becd24d422a2e55582e222ad6a89e /doc/s6-linux-init-logouthookd.html | |
| parent | 9e6d0f168bf59df9cd829d6ebe63fb08ea9ae01e (diff) | |
| download | s6-linux-init-1bfba3b0be32306b078f5ee527b864e758b2c77b.tar.xz | |
Make a single hpr. Full doc, first draft.
Diffstat (limited to 'doc/s6-linux-init-logouthookd.html')
| -rw-r--r-- | doc/s6-linux-init-logouthookd.html | 84 |
1 files changed, 84 insertions, 0 deletions
diff --git a/doc/s6-linux-init-logouthookd.html b/doc/s6-linux-init-logouthookd.html new file mode 100644 index 0000000..34f5bd8 --- /dev/null +++ b/doc/s6-linux-init-logouthookd.html @@ -0,0 +1,84 @@ +<html> + <head> + <meta name="viewport" content="width=device-width, initial-scale=1.0" /> + <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /> + <meta http-equiv="Content-Language" content="en" /> + <title>s6-linux-init: the s6-linux-init-logouthookd program</title> + <meta name="Description" content="s6-linux-init: the s6-linux-init-logouthookd program" /> + <meta name="Keywords" content="s6-linux-init command s6-linux-init-logouthookd login logout utmp hook sysvinit" /> + <!-- <link rel="stylesheet" type="text/css" href="//skarnet.org/default.css" /> --> + </head> +<body> + +<p> +<a href="index.html">s6-linux-init</a><br /> +<a href="//skarnet.org/software/">Software</a><br /> +<a href="//skarnet.org/">skarnet.org</a> +</p> + +<h1> The <tt>s6-linux-init-logouthookd</tt> program </h1> + +<p> + s6-linux-init-logouthookd cleans up its client's utmp record when it dies. +</p> + +<h2> Interface </h2> + +<pre> + s6-ipcserver <em>socket</em> s6-linux-init-logouthookd +</pre> + +<p> + s6-linux-init-logouthookd implements a +<a href="//skarnet.org/software/s6/localservice.html">local service</a> +for getty programs that add an utmp record when a user logs in. +</p> + +<p> + In the sysvinit model, <tt>getty</tt>/<tt>login</tt> and similar programs add an utmp +record for every user that logs in, then exec into the user's shell. +At logout time, the shell dies; sysvinit is supervising the <tt>getty</tt> +program, so it's watching the pid, and respawns the <tt>getty</tt> when the +shell dies. But before respawning the <tt>getty</tt>, it cleans up the +utmp record, to correctly report that the user isn't logged in on this +terminal anymore. +</p> + +<p> + utmp is an old, clunky, insecure system (unless you're using +<a href="//skarnet.org/software/utmps/">utmps</a>) and it is definitely +not pid 1's job to have any knowledge of utmp and play janitor after +<tt>getty</tt>. <a href="//skarnet.org/software/s6/s6-svscan.html">s6-svscan</a> +definitely will not do it. +</p> + +<p> + Some distributions use versions of <tt>login</tt> that fork the user's +shell instead of execing it. When the user logs out, the <tt>login</tt> +program cleans up after itself. This is a better model, but it's not +always easy to patch <tt>login</tt> to go from a "exec the shell" model to a +"fork the shell as a child" model. +</p> + +<p> + <tt>s6-linux-init</tt> comes with a small library which makes it easy +for a distribution to fully support utmp cleanup with an s6 init system +if they so choose. Before execing into the user's shell, the <tt>login</tt> +program should just make a call to <tt>s6_linux_init_logouthook()</tt>, +and that's it. That function will call the <tt>s6-linux-init-logouthookd</tt> +local service, which will do nothing but wait until the user's shell dies; +and when it happens, the user's utmp record will automatically be cleaned up. +</p> + +<h2> Notes </h2> + +<ul> + <li> The <a href="//skarnet.org/software/s6/localservice.html">local service</a> +implementing logouthook support is automatically created at boot time when the +<tt>-L</tt> option has been given to +<a href="s6-linux-init-maker">s6-linux-init-maker</a>. Client-side, though, +the various login programs must be patched at the source level. </li> +</ul> + +</body> +</html> |