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<title>s6: the s6-usertree-maker program</title>
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<p>
<a href="index.html">s6</a><br />
<a href="//skarnet.org/software/">Software</a><br />
<a href="//skarnet.org/">skarnet.org</a>
</p>
<h1> The s6-usertree-maker program </h1>
<p>
s6-usertree-maker creates a <a href="servicedir.html">service directory</a>
implementing a service that runs an <a href="s6-svscan.html">s6-svscan</a>
process owned by a given user, on a <a href="scandir.html">scan directory</a>
belonging to that user. It is meant to help admins deploy systems where
each user has their own supervision subtree, rooted in the main supervision
tree owned by root.
</p>
<p>
Alternatively, s6-usertree-maker can create source definition directories
for the <a href="//skarnet.org/software/s6-rc/">s6-rc</a> service manager.
</p>
<h2> Interface </h2>
<pre>
s6-usertree-maker \
[ -d <em>userscandir</em> ] \
[ -p <em>path</em> ] \
[ -E <em>envdir</em> [ -e <em>var</em> -e <em>var</em> ... ] ] \
[ -r <em>service</em>/<em>logger</em>[/<em>pipeline</em>] ] \
[ -l <em>loguser</em> ] \
[ -t <em>stamptype</em> ] \
[ -n <em>nfiles</em> ] \
[ -s <em>filesize</em> ] \
[ -S <em>maxsize</em> ] \
[ -P <em>prefix</em> ] \
user logdir dir
</pre>
<p>
s6-usertree-maker creates a service directory in <em>dir</em>, that launches
a supervision tree as user <em>user</em> on scan directory <em>userscandir</em>,
with a catch-all logger logging the tree's output via
<a href="s6-log.html">s6-log</a> to the <em>logdir</em> directory.
</p>
<h2> Exit codes </h2>
<ul>
<li> 0: success </li>
<li> 100: wrong usage </li>
<li> 111: system call failed </li>
</ul>
<h2> Options </h2>
<ul>
<li> <tt>-d</tt> <em>userscandir</em> : the supervision tree will be run
on the <em>userscandir</em> directory. <em>userscandir</em> is subject to variable
substitution (see below). Default is <strong><tt>${HOME}/service</tt></strong>. </li> <br />
<li> <tt>-p</tt> <em>path</em> : the supervision tree will be run with a
PATH environment variable set to <em>path</em>. <em>path</em> is subject to variable
substitution. Default is <strong><tt>/usr/bin:/bin</tt></strong>, or whatever has been
given to the <tt>--with-default-path</tt> option to skalibs' configure script. </li> <br />
<li> <tt>-E</tt> <em>envdir</em> : the supervision tree will be run with
the environment variables defined in the directory <em>envdir</em>, which will be
read via <a href="s6-envdir.html">s6-envdir</a> without options. By default, no
envdir is defined and the supervision tree will only be run with the basic
environment variables listed below. </li> <br />
<li> <tt>-e</tt> <em>var</em> : Perform variable substitution on <em>var</em>.
This option is repeatable, and only makes sense when the <tt>-E</tt> option is also
given. For every <em>var</em> listed via a <tt>-e</tt> option, the contents of
<em>var</em> will be subjected to variable substitution before the supervision tree
is run. This is only useful if <em>var</em> is defined in <em>envdir</em>, as a
template, that is then instanced for <em>user</em> when the service is run. By
default, only the PATH environment variable, customizable via <tt>-p</tt>, is
subjected to variable substitution. </li> <br />
<li> <tt>-r</tt> <em>service</em>/<em>logger</em>/<em>pipeline</em> :
create <a href="//skarnet.org/software/s6-rc">s6-rc</a> source definition directories.
When this option is given, <em>dir</em> is not created as a service directory, but
as a directory containing two services: <em>dir</em>/<em>service</em> and
<em>dir</em>/<em>logger</em>, and <em>dir</em> is suitable as a source argument to
<a href="//skarnet.org/software/s6-rc/s6-rc-compile.html">s6-rc-compile</a>. The
<tt>/</tt><em>pipeline</em> part can be omitted, but if it is present, <em>pipeline</em>
is used as a name for a bundle containing both <em>service</em> and <em>logger</em>.
When this option is not given, <em>dir</em> is a regular service directory for direct
inclusion (or linking) in the parent scan directory (and the catch-all logger for
the user subtree is declared in <em>dir</em><tt>/log</tt>). </li> <br />
<li> <tt>-l</tt> <em>loguser</em> : run the catch-all logger of the user
subdirectory as user <em>loguser</em>. Default is <strong><tt>root</tt></strong>. </li> <br />
<li> <tt>-t</tt> <em>stamptype</em> : how
logs are timestamped by the catch-all logger. 0 means no
timestamp, 1 means
<a href="https://cr.yp.to/libtai/tai64.html">external TAI64N format</a>,
2 means
<a href="https://www.iso.org/iso/home/standards/iso8601.htm">ISO 8601 format</a>,
and 3 means both. Default is <strong><tt>1</tt></strong>. </li> <br />
<li> <tt>-n</tt> <em>nfiles</em> : maximum number of archive files
in <em>logdir</em>. Default is <strong><tt>10</tt></strong>. </li> <br />
<li> <tt>-s</tt> <em>filesize</em> : maximum size of the <tt>current</tt>
file (and archive files) in <em>logdir</em>. Default is <strong><tt>1000000</tt></strong>. </li> <br />
<li> <tt>-S</tt> <em>maxsize</em> : maximum total size of the
archives in the <em>logdir</em>. Default is <strong><tt>0</tt></strong>,
meaning no limits apart from those enforced by the <tt>-n</tt> and
<tt>-s</tt> options. </li> <br />
<li> <tt>-P</tt> <em>prefix</em> : when logging to <em>logdir</em>,
prefix logged lines with the <em>prefix</em> string. </li> <br />
</ul>
<h2> Operation of the service </h2>
<p>
When the service is started, its run script will execute the following
operations:
</p>
<ul>
<li> Clear all its environment variables, except PATH. This prevents
any data leak from the parent supervision tree into the user subtree. </li>
<li> Fill its environment with data related to <em>user</em>:
<ul>
<li> USER is set to <em>user</em> </li>
<li> HOME is set to <em>user</em>'s home directory </li>
<li> UID is set to <em>user</em>'s uid </li>
<li> GID is set to <em>user</em>'s primary gid </li>
<li> GIDLIST is set to <em>user</em>'s supplementary groups list </li>
</ul> </li>
<li> If the service has been created with the <tt>-E</tt> option to s6-usertree-maker:
<ul>
<li> Add all the variables defined in <em>envdir</em> to its environment </li>
<li> For every variable <em>var</em> given via a <tt>-e</tt> option, subject
<em>var</em> to substitution with the USER, HOME, UID, GID and GIDLIST variables
(see below). </li>
</ul> </li>
<li> Set the PATH environment variable to <em>path</em>, subjected to
variable substitution. </li>
<li> Execute into <a href="s6-svscan.html">s6-svscan</a>, running in
<em>userscandir</em> (which is first subjected to variable substitution). </li>
</ul>
<p>
The service is logged: its stderr and stdout are piped to an
<a href="s6-log.html">s6-log</a> process running as <em>loguser</em> and
writing to the <em>logdir</em> directory. This logger is the catch-all logger
for the supervision tree owned by <em>user</em>; it is recommended to make
<em>loguser</em> distinct from <em>user</em>, and to have <em>logdir</em>
in a place that is <strong>not</strong> under the control of <em>user</em>.
If <em>user</em> wants to keep control of their logs, they can declare a
logger for each of their services.
</p>
<h2> Variable substitution </h2>
<p>
When the service starts, the USER, HOME, UID, GID and GIDLIST
environment variables are deduced from <em>user</em>'s identity.
The value of those variables may be used in a few configuration
knobs:
</p>
<ul>
<li> The value of <em>userscandir</em>: it is likely that the
scan directory belonging to <em>user</em> resides under <em>user</em>'s
home directory. Or under <tt>/run/user/${UID}</tt>, or some similar
scheme. </li>
<li> The PATH environment variable, declared in <em>path</em>: it is
often useful to prepend the default system PATH with a user-specific
directory that hosts that user's binaries. For instance, you may want
the PATH to be set as something like <tt>${HOME}/bin:/usr/bin:/bin</tt>. </li>
<li> Any variable declared in <em>envdir</em> and given as an argument
to a <tt>-e</tt> option to s6-usertree-maker. If <em>envdir</em> is a
template valid for all users, it may contain variables that depends on
user-specific data: for instance, the XDG_CONFIG_HOME variable may be
set to <tt>${HOME}/.config</tt>. </li>
</ul>
<p>
When the strings <tt>${USER}</tt>, <tt>${HOME}</tt>, <tt>${UID}</tt>,
<tt>${GID}</tt>, or <tt>${GIDLIST}</tt> appear in the value for
<em>userscandir</em>, <em>path</em>, or any of the <em>var</em>
variables, they are substituted with the corresponding value of the USER,
HOME, UID, GID, or GIDLIST environment variable instead.
</p>
<p>
For instance, if no <tt>-d</tt> option is provided, the default value
for <em>userscandir</em> is <tt>${HOME}/service</tt>. If the provided
<em>user</em> is <tt>ska</tt> and ska's home directory is <tt>/home/ska</tt>,
then <a href="s6-svscan.html">s6-svscan</a> will be run on
<tt>/home/ska/service</tt>.
</p>
<h2> Examples </h2>
<pre>
s6-usertree-maker -d '/run/user/${UID}/service' -p '${HOME}/bin:/usr/bin:/bin' -E /etc/user-env -e XDG_CONFIG_HOME -l catchlog ska /var/log/usertree/ska usertree-ska
</pre>
<p>
creates a service directory in <tt>usertree-ska</tt> declaring a service that
starts a supervision tree on <tt>/run/user/1000/service</tt> if ska has uid 1000,
with <tt>/home/ska/bin:/usr/bin/bin</tt> as its PATH if ska's home directory is
<tt>/home/ska</tt>, and with all the environment variables declared in
<tt>/etc/user-env</tt>, among which the XDG_CONFIG_HOME variable is processed
for variable substitution. The supervision tree has a catch-all logger running
as user catchlog, and storing its data in the <tt>/var/log/usertree/ska</tt>
directory.
</p>
<p>
Note that simple quotes are used here to prevent the shell from
interpreting <tt>${UID}</tt> and <tt>${HOME}</tt>.
</p>
<pre>
s6-usertree-maker -d '/run/user/${UID}/service' -p '${HOME}/bin:/usr/bin:/bin' -E /etc/user-env -e XDG_CONFIG_HOME -l catchlog -r usertree-ska/usertree-ska-log/usertree-ska-pipeline ska /var/log/usertree/ska usertree
</pre>
<p>
Same as above, except it does not create a service directory — instead, it
creates a <tt>usertree</tt> directory containing two subdirectories: <tt>usertree-ska</tt>, the
<a href="//skarnet.org/software/s6-rc/">s6-rc</a> source definition directory
for the service, and <tt>usertree-ska-log</tt>, the source definition directory
for its logger. It also creates an implicit <tt>usertree-ska-pipeline</tt> bundle
containing both the service and the logger.
</p>
<h2> Notes </h2>
<ul>
<li> s6-usertree-maker makes use of the fact that
<a href="//skarnet.org/software/execline/">execline</a> scripts are much
easier to generate programmatically and to harden than shell scripts, so it is only
built if s6 is built with <a href="//skarnet.org/software/execline/">execline</a>
support - i.e. the <tt>--disable-execline</tt> switch has <em>not</em> been given
to configure. </li>
<li> For the admin who wants to automate user tree management, s6-usertree-maker
is a <em>building block</em> meant to be used in scripts, not a complete turnkey
solution. For instance, s6-usertree-maker does not create <em>userscandir</em> for
a user: it assumes that that scandir is already in place. It does not create
<em>logdir</em> either: <em>logdir</em>, or at least its parent directory, must
already exist before the logger is run, else <a href="s6-log.html">s6-log</a> will
fail repeatedly. Make sure that all the data and metadata referenced by the service's
and the logger's run scripts are actually present and valid before starting the
service. </li>
<li> If s6-usertree-maker encounters failure (and exits 111), it does not clean up
the directories it created. Make sure to always test s6-usertree-maker's return code
and clean up after it if needed. </li>
</ul>
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