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<title>s6-portable-utils: the s6-ln program</title>
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<h1> The <tt>s6-ln</tt> program </h1>
<p>
s6-ln creates a link to a file.
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<h2> Interface </h2>
<pre>
s6-ln [ -n ] [ -s ] [ -f ] [ -L ] [ -P ] <em>source...</em> <em>target</em>
</pre>
<p>
s6-ln acts as the generic
<a href="https://pubs.opengroup.org/onlinepubs/9699919799/utilities/ln.html">ln</a> utility.
</p>
<h2> Options </h2>
<ul>
<li> <tt>-s</tt> : create a symbolic link instead of a hard link </li>
<li> <tt>-f</tt> : force replacement of an existing <em>target</em> </li>
<li> <tt>-L</tt> : link targets of symlinks in <em>source...</em> </li>
<li> <tt>-P</tt> : link symlinks in <em>source...</em> themselves </li>
<li> <tt>-n</tt> : if <em>target</em> is a symlink to a directory, replace
it instead of adding a link in the directory </li>
</ul>
<h2> Posixness </h2>
<p>
s6-ln <strong>would be</strong> suitable as a Single Unix
<a href="https://pubs.opengroup.org/onlinepubs/9699919799/utilities/ln.html">ln</a>
program, except that POSIX mandates that a preexisting <em>target</em> must first
be <tt>unlink()</tt>ed and then (<tt>sym</tt>)<tt>link()</tt>ed, which prevents
atomic replacements.
<tt>s6-ln</tt> aims to be reliable and allow for atomic replacements, so it
deviates from POSIX on that point: when <em>target</em> exists and needs to
be replaced, <tt>s6-ln</tt> first creates a (sym)link to a unique temporary
name, then <tt>rename()</tt>s the temporary name to <em>target</em>. This
behaviour makes sure that <em>target</em> is atomically replaced - there's
no point in time where it does not exist.
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