#16930: more explanation in the guide for startupitems ------------------------------------------------+--------------------------- Reporter: dweber@macports.org | Owner: markd@macports.org Type: enhancement | Status: new Priority: Normal | Milestone: Website & Documentation Component: guide | Version: 1.6.0 Keywords: startupitem daemondo launchd guide | Port: ------------------------------------------------+--------------------------- I found the guide for startupitems is too terse, without adequate background explanation of the tools that implement the process. Please include information on how to get further information, such as: {{{ man launchd man launchctl daemondo --help }}} The latter is helpful, as {{{man daemondo}} doesn't exist (can we create it?). In my case, I found it useful to read through the entire thread that was engaged during the creation of the guide for this section (esp. comments therein from James Berry), ie: Ryan Schmidt, "daemondo defeats purpose of launchd?" at http://lists.macosforge.org/pipermail/macports- dev/2007-September/002669.html If I had time and an understanding of the documentation dev process, I would contribute directly, but it may be easier for the current dev folks to update this section of the guide. I would really like to see a few paragraphs from James' comments adapted into the background for this section of the guide. His comments are succinct and illuminating (esp. in the context of that thread). For example, {{{ daemondo will indeed quit when it detects that the launched process has quit, and thus will "keep alive" the process, since launchd will then restart daemondo. In this way, daemondo acts as a shim or adapter between the scripts supported by the startupitem command, and the single process expected by launchd. The reason that startupitem.executable is preferred is that this gives the best possible chance that daemondo will be able to detect the death of the launched process: since daemondo can launch the process, it can also detect when it quits, stop it, etc. For those cases where startupitem.executable cannot be used, daemondo also supports the startupitem.pidfile commands that allow the process' pidfile to be monitored: daemondo will read the pidfile and watch for the death of that process. So daemondo, and thus launchd, will be aware of the daemon process death (and be able to restart the daemon process) only under two circumstances: (1) startupitem.executable was supplied (thus daemondo starts the process) (2) startupitem.pidfile was supplied (thus daemondo reads the process id) Under all other circumstances, daemondo will not know that the daemon process has died, and will not exit when the process does die, and thus launchd won't restart the process since it doesn't know it died. Put another way, if daemondo can know the process has died, then launchd will know too, but not otherwise. }}} {{{ Note that for simplicity, startupitem.executable is handled by daemondo at present. This has two purposes: - It keeps the startupitem generating code a little simpler. - It allows the potential support for higher value services to be provided by daemondo. In particular, note daemondo's --restart- netchange option, which can be quite useful, but for which there is no current support by the startupitem keys. }}} Also, later in the thread, we have some comments that could be adapted for the guide: {{{ ... I don't see the incompatibility of those statements, but then I again I know what i meant, not necessarily what it means to others ;). The later sentence, btw, is missing a word on the end. It should read: "the pidfile keyword is likely useful only if the executable keyword is not specified." Does that help any?

Looks to me like startupitem.pidfile must be set for a deamon to be tracked whether it is executable startupitem or not.

No, daemondo will track an "executable" in an case (and it doesn't need to know where their pidfile is, generally, since it launches the code and thus knows the pid). In the case of script code (non "executable") daemondo doesn't know the pid, since it doesn't know what the script code did. In this case, it has to rely on reading a pidfile to get the process id, or else simply not know.

And the man page says startupitem.pidfile is "particularly useful" for startupitem.executable. Can you explain this?

That was either garbage to begin with, or else got messed up in creation of the man page. Off the top of my head I can't see any particular reason to use a pidfile keyword in conjunction with the executable keyword, unless it's to specify that it should delete a pidfile created by the executable, and I'm not sure that even works for that case. Hope that helps. James }}} Best, Darren PS, In the description of the startupitem.pidfile, can we remove the OR operator, ie: {{{ Default: [none] | [${prefix}/var/run/${name}.pid] }}} It's easy to confuse this syntax as either: {{{ Default: [none] }}} OR {{{ Default: [${prefix}/var/run/${name}.pid] }}} However, we do need two arguments: [daemondoAction] [pidFile] -- Ticket URL: <http://trac.macports.org/ticket/16930> MacPorts <http://www.macports.org/> Ports system for Mac OS