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Diffstat (limited to 'doc/s6-svscan.html')
| -rw-r--r-- | doc/s6-svscan.html | 58 |
1 files changed, 54 insertions, 4 deletions
diff --git a/doc/s6-svscan.html b/doc/s6-svscan.html index a0a6790..6c4d8d9 100644 --- a/doc/s6-svscan.html +++ b/doc/s6-svscan.html @@ -27,7 +27,7 @@ the root or a branch of a <em>supervision tree</em>. <h2> Interface </h2> <pre> - s6-svscan [ -c max ] [ -t <em>rescan</em> ] [ <em>scandir</em> ] + s6-svscan [ -S | -s ] [ -c max ] [ -t <em>rescan</em> ] [ <em>scandir</em> ] </pre> <ul> @@ -59,6 +59,9 @@ execution. </li> <h2> Options </h2> <ul> + <li> <tt>-S </tt> : do not divert signals. This is the default for now; +it may change in a future version of s6. </li> + <li> <tt>-s </tt> : divert signals - see below. </li> <li> <tt>-c <em>max</em></tt> : maintain services for up to <em>max</em> service directories. Default is 500. Lower limit is 2. There is no upper limit, but: <ul> @@ -82,20 +85,67 @@ scan (and a reap) every 5 seconds. It is <em>strongly</em> discouraged to set <h2> Signals </h2> <p> - s6-svscan reacts to the following signals: + s6-svscan always reacts to the following signals: </p> <ul> <li> SIGCHLD : triggers the reaper. </li> <li> SIGALRM : triggers the scanner. </li> + <li> SIGABRT : acts as if a <tt>s6-svscanctl -b</tt> command had been received. </li> +</ul> + +<p> + By default, it also reacts to the following signals: +</p> + +<ul> <li> SIGTERM : acts as if a <tt>s6-svscanctl -t</tt> command had been received. </li> <li> SIGHUP : acts as if a <tt>s6-svscanctl -h</tt> command had been received. </li> <li> SIGQUIT : acts as if a <tt>s6-svscanctl -q</tt> command had been received. </li> - <li> SIGABRT : acts as if a <tt>s6-svscanctl -b</tt> command had been received. </li> <li> SIGINT : acts as if a <tt>s6-svscanctl -6</tt> command had been received. </li> - <li> SIGUSR1 : acts as if a <tt>s6-svscanctl -7</tt> command had been received. </li> </ul> +<p> + But if the <tt>-s</tt> option was given, then instead of those default actions, +s6-svscan uses configurable handlers: it forks and executes a program every time +it receives one of the following signals. +</p> + +<ul> + <li> SIGTERM : fork and execute <tt>.s6-svscan/SIGTERM</tt> </li> + <li> SIGHUP : fork and execute <tt>.s6-svscan/SIGHUP</tt> </li> + <li> SIGQUIT : fork and execute <tt>.s6-svscan/SIGQUIT</tt> </li> + <li> SIGINT : fork and execute <tt>.s6-svscan/SIGINT</tt> </li> + <li> SIGUSR1 : fork and execute <tt>.s6-svscan/SIGUSR1</tt> </li> + <li> SIGUSR2 : fork and execute <tt>.s6-svscan/SIGUSR2</tt> </li> +</ul> + +<p> + If an action cannot be taken (the relevant file doesn't exist, or isn't +executable, or any kind of error happens), s6-svscan prints a warning +message to its standard error but does nothing else with the signal. +</p> + +<p> + The <tt>-s</tt> mechanism is useful, for instance, when s6-svscan is running as +process 1 and needs to trap signals such as SIGINT (sent on some systems by +a Ctrl-Alt-Del press) in order to perform some specific work instead of +executing into <tt>.s6-svscan/finish</tt> on the spot. +</p> + +<p> + s6-svscan will not exit its loop on its own when it receives a signal such as +SIGINT and the <tt>-s</tt> option has been given. To make it exit its loop, +invoke a <a href="s6-svscanctl.html">s6-svscanctl</a> command from the signal +handling script. For instance, a <tt>.s6-svscan/SIGINT</tt> script could look +like this: +</p> + +<pre> #!/command/execlineb -P + foreground { shutdown-the-services } + s6-svscanctl -i . +</pre> + <h2> The reaper </h2> <p> |