September 2008 - Darwin-dev

Re: launchd daemon, spawning children?
by Garth Cummings 25 Sep '08

25 Sep '08

site_archiver(a)lists.apple.com Delivered-To: Darwin-dev(a)lists.apple.com Hi Mario, On Sep 25, 2008, at 2:09 PM, Mario Emmenlauer wrote: Hi Garth, A good place to start is the UNIX 03 spec itself: <http://www.unix.org/single_unix_specification/> For the fork-problem, however, my previous reference http://developer.apple.com/documentation/MacOSX/Conceptual/BPSystemStartup/… But it leaves aside how the standard tasks are to be performed on the Mac, then :-D Have you read Technical Note TN2083 "Daemons and Agents"? <http://developer.apple.com/technotes/tn2005/tn2083.html> Cheers, Mario --gc ____________________________________________________________________ Garth Cummings gcummings(a)apple.com Sr. Software Engineer Apple Developer Technical Support <http://developer.apple.com/technicalsupport> _______________________________________________ Do not post admin requests to the list. They will be ignored. Darwin-dev mailing list (Darwin-dev(a)lists.apple.com) Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/darwin-dev/site_archiver%40lists.app… Garth Cummings wrote: On Sep 25, 2008, at 1:12 PM, Mario Emmenlauer wrote: Searching apple.com for posix_spawn() lists almost exclusively the manpages of the functions, no more. That's indeed a good reference, thanks. For getting started it would be good to have additionally something with more overview, like the technotes. The technotes on Carbon and launchd I found extremely good. They specify nicely what the design-idea of Mac OS is. even notes: [...] Although many of the preceding behaviors may be standard tasks for daemons to perform, they are not recommended when running under launchd. [...] This email sent to site_archiver(a)lists.apple.com

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Re: launchd daemon, spawning children?
by Mario Emmenlauer 25 Sep '08

25 Sep '08

site_archiver(a)lists.apple.com Delivered-To: Darwin-dev(a)lists.apple.com User-agent: Mozilla-Thunderbird 2.0.0.16 (X11/20080724) Hi Garth, On Sep 25, 2008, at 1:12 PM, Mario Emmenlauer wrote: A good place to start is the UNIX 03 spec itself: That's indeed a good reference, thanks. For getting started it would be good to have additionally something with more overview, like the technotes. The technotes on Carbon and launchd I found extremely good. They specify nicely what the design-idea of Mac OS is. For the fork-problem, however, my previous reference http://developer.apple.com/documentation/MacOSX/Conceptual/BPSystemStartup/… even notes: [...] Although many of the preceding behaviors may be standard tasks for daemons to perform, they are not recommended when running under launchd. [...] But it leaves aside how the standard tasks are to be performed on the Mac, then :-D Cheers, Mario _______________________________________________ Do not post admin requests to the list. They will be ignored. Darwin-dev mailing list (Darwin-dev(a)lists.apple.com) Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/darwin-dev/site_archiver%40lists.app… Garth Cummings wrote: Searching apple.com for posix_spawn() lists almost exclusively the manpages of the functions, no more. <http://www.unix.org/single_unix_specification/> This email sent to site_archiver(a)lists.apple.com

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Re: launchd daemon, spawning children?
by Damien Sorresso 25 Sep '08

25 Sep '08

site_archiver(a)lists.apple.com Delivered-To: Darwin-dev(a)lists.apple.com . . . See the following documentation... launchd.plist(5) launchd(8) http://developer.apple.com/technotes/tn2005/tn2083.html#SECDAEMONOMICON -- Damien Sorresso BSD Engineering Apple Inc. dsorresso(a)apple.com 408.974.7488 _______________________________________________ Do not post admin requests to the list. They will be ignored. Darwin-dev mailing list (Darwin-dev(a)lists.apple.com) Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/darwin-dev/site_archiver%40lists.app… This email sent to site_archiver(a)lists.apple.com On Sep 25, 2008, at 9:40 AM, Mario Emmenlauer wrote: I have a problem understanding how things are done in a system- conform way on the Mac. If this is not the right mailing list for daemon questions, please point me to the correct one. I want to write a (launchd) daemon that needs to execute processes upon certain events. This poses quite a problem (to me?), especially if I want to start the process as a dynamically changing user which is typically not the current GUI user. 4) Using launchd() works great: launch_data_t msg = launch_data_alloc(LAUNCH_DATA_DICTIONARY); launch_data_dict_insert(msg,launch_data_new_string("com.c.App"), LAUNCH_KEY_STARTJOB); launch_data_t resp = launch_msg(msg); but I am missing an interface to set the user. Of course a fixed user can be chosen in the plist, but then its not dynamic. Also, I can start an app as root with launchd and setuid from within this app, but if someone exchanges the app, he will gain root access. See launchd.plist(5). You can only set a UserName key in a daemon running under the system launchd. Though if you're looking to launch applications in user sessions from a root-owned daemon, you're almost certainly going about it wrong. To launch an application in a user session, you first have to get that user's session up and running if it isn't already. We don't want third- party developers trying to bootstrap user sessions. I would strongly suggest creating an agent that runs for every user, is limited to the Aqua session, listens for events and launches the appropriate application using the appropriate high-level APIs found in the LaunchServices or AppKit frameworks. Am I missing something in the launchd API interface? How would one typically write an ftp-daemon on Mac OS (i.e. write a daemon that runs as root, then spawns a child that runs as the user that requests ftp login)? smime.p7s

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Re: launchd daemon, spawning children?
by Garth Cummings 25 Sep '08

25 Sep '08

site_archiver(a)lists.apple.com Delivered-To: Darwin-dev(a)lists.apple.com _______________________________________________ Do not post admin requests to the list. They will be ignored. Darwin-dev mailing list (Darwin-dev(a)lists.apple.com) Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/darwin-dev/site_archiver%40lists.app… This email sent to site_archiver(a)lists.apple.com

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Re: launchd daemon, spawning children?
by Jason Coco 25 Sep '08

25 Sep '08

site_archiver(a)lists.apple.com Delivered-To: Darwin-dev(a)lists.apple.com Dkim-signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=domainkey-signature:received:received:cc:message-id:from:to :in-reply-to:content-type:mime-version:subject:date:references :x-mailer; bh=K92298ItEbc1t6Iv8dcBi5LzUL85edPghHkuGrSLyMc=; b=pOFDXIGQlqOJriorVfUzqBl/ekZnqFiBcQoe58cNxDvLnm/3i+BnpaCkT7CrDQzpch tGusOVdIJ8SJOk537cIehrIvEJ+Jz9p+Cv2OCQf0FMW4AmRHHpibkwo5dtgg1fFqSEMj WBOlmujmvgdBsWsI9nw33erapA/vOkXlZbZ18= Domainkey-signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=cc:message-id:from:to:in-reply-to:content-type:mime-version:subject :date:references:x-mailer; b=U7FXVgOEbGpbn//rqEKHSfWRlvy+ixyYlAteIdgJOG0r3sMtRuPMw8nDpFgrbOz5FE pxwRiMsr73Q4ZmiCkTpB4dz1T4pZT8Z5y8xOJyiwtblakoBzwOH0MgO5b0vSnzwCGk7i YTt6dX4l/s/mMI7Ru49qjFCXATbdbUrzoKrhs= On Sep 25, 2008, at 16:12 , Mario Emmenlauer wrote: Hi Terry, Is this allowed behaviour for a launchd-daemon? From: http://developer.apple.com/documentation/MacOSX/Conceptual/BPSystemStartup/… and: [...] Do not close any stray file descriptors. [...] Jason _______________________________________________ Do not post admin requests to the list. They will be ignored. Darwin-dev mailing list (Darwin-dev(a)lists.apple.com) Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/darwin-dev/site_archiver%40lists.app… This email sent to site_archiver(a)lists.apple.com thanks for the quick, and really extensive reply! Can you (or somebody) point me to a good readme/technote/book on Mac OS standards? Searching apple.com for posix_spawn() lists almost exclusively the manpages of the functions, no more. Terry Lambert wrote: On Sep 25, 2008, at 9:50 AM, Mario Emmenlauer wrote: 2) I haven't tried pthread_start(), but its very likely to be equal This should have been posix_spawn(), not pthread_start()... but come on, they do sound similar :-D posix_spawn() is morally equivalent to a vfork() followed by an execve(), with the ability to do a limited set of intermediate work in between. I took: [...] This includes calling the daemon function, calling fork followed by exec, or calling fork followed by exit. [...] The documentation is not consistent in disallowed behaviour. The launchctl.plist manpage for example discourages calling fork()/exit() only for the parent process (not for the child), and only because launchd might assume it quit unexpectedly. You can call fork/exec inside your launchd daemon, what the documentation is talking about is backgrounding the daemon. That you're not allowed to do (i.e., fork/ exec then exit from the parent). As long as the parent gets managed by launchd and stays around when it's supposed to, you can spawn other processes. The second part of the documentation just notes that you shouldn't close stray file descriptors... it's not really a conflict. smime.p7s

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Re: launchd daemon, spawning children?
by Mario Emmenlauer 25 Sep '08

25 Sep '08

site_archiver(a)lists.apple.com Delivered-To: Darwin-dev(a)lists.apple.com User-agent: Mozilla-Thunderbird 2.0.0.16 (X11/20080724) Hi Terry, thanks for the quick, and really extensive reply! Can you (or somebody) point me to a good readme/technote/book on Mac OS standards? Searching apple.com for posix_spawn() lists almost exclusively the manpages of the functions, no more. This should have been posix_spawn(), not pthread_start()... but come on, they do sound similar :-D Is this allowed behaviour for a launchd-daemon? From: http://developer.apple.com/documentation/MacOSX/Conceptual/BPSystemStartup/… I took: [...] This includes calling the daemon function, calling fork followed by exec, or calling fork followed by exit. [...] and: [...] Do not close any stray file descriptors. [...] The documentation is not consistent in disallowed behaviour. The launchctl.plist manpage for example discourages calling fork()/exit() only for the parent process (not for the child), and only because launchd might assume it quit unexpectedly. Is pid = fork() if (pid == 0) { exec("worker"); // work exit(); } else { // do nothing } a problem? Thanks and cheers, Mario _______________________________________________ Do not post admin requests to the list. They will be ignored. Darwin-dev mailing list (Darwin-dev(a)lists.apple.com) Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/darwin-dev/site_archiver%40lists.app… Terry Lambert wrote: On Sep 25, 2008, at 9:50 AM, Mario Emmenlauer wrote: 2) I haven't tried pthread_start(), but its very likely to be equal posix_spawn() is morally equivalent to a vfork() followed by an execve(), with the ability to do a limited set of intermediate work in between. This email sent to site_archiver(a)lists.apple.com

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Re: launchd daemon, spawning children?
by Terry Lambert 25 Sep '08

25 Sep '08

site_archiver(a)lists.apple.com Delivered-To: Darwin-dev(a)lists.apple.com Hi, oldeuid = geteuid(); oldegid = getgid(); realoldgroupcount = getgroups(16, oldsgrouplist); seteuid(neweuid); posix_spawn(...) seteuid(oldeuid); setgroups(realoldgroupcount, newgroupslist); setegid(newgid); -- Terry _______________________________________________ Do not post admin requests to the list. They will be ignored. Darwin-dev mailing list (Darwin-dev(a)lists.apple.com) Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/darwin-dev/site_archiver%40lists.app… On Sep 25, 2008, at 9:50 AM, Mario Emmenlauer wrote: 2) I haven't tried pthread_start(), but its very likely to be equal This should have been posix_spawn(), not pthread_start()... but come on, they do sound similar :-D posix_spawn() is morally equivalent to a vfork() followed by an execve(), with the ability to do a limited set of intermediate work in between. Part of the limited set of work is controlled by the flags set via posix_spawnattr_setflags(), and one of those flags is POSIX_SPAWN_RESETIDS. Depending on how you are running the parent process at the time of the spawn, you can either set this flag, and inherit the real uid/gid, or not set the flag and inherit the effective uid/gid. Since we support proper security partitioning (POSIX saved IDs + non- library setreuid() and setregid()), your most correct path would be to run as root and: ...the get and setegid are not necessary on MacOS X, since they are included in the supplementary groups list, but you will include them if you want your code to be portable to e.g. Solaris. This email sent to site_archiver(a)lists.apple.com

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Re: launchd daemon, spawning children?
by Mario Emmenlauer 25 Sep '08

25 Sep '08

site_archiver(a)lists.apple.com Delivered-To: Darwin-dev(a)lists.apple.com User-agent: Thunderbird 2.0.0.16 (Macintosh/20080707) Hi, This should have been posix_spawn(), not pthread_start()... but come on, they do sound similar :-D Cheers, Mario _______________________________________________ Do not post admin requests to the list. They will be ignored. Darwin-dev mailing list (Darwin-dev(a)lists.apple.com) Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/darwin-dev/site_archiver%40lists.app… 2) I haven't tried pthread_start(), but its very likely to be equal This email sent to site_archiver(a)lists.apple.com

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launchd daemon, spawning children?
by Mario Emmenlauer 25 Sep '08

25 Sep '08

site_archiver(a)lists.apple.com Delivered-To: Darwin-dev(a)lists.apple.com User-agent: Thunderbird 2.0.0.16 (Macintosh/20080707) Hi, I have a problem understanding how things are done in a system- conform way on the Mac. If this is not the right mailing list for daemon questions, please point me to the correct one. I want to write a (launchd) daemon that needs to execute processes upon certain events. This poses quite a problem (to me?), especially if I want to start the process as a dynamically changing user which is typically not the current GUI user. 1) I should not use the fork/exec() combination in a daemon. And besides it causes major problems with closing file descriptors, and sometimes even crashes my App. 2) I haven't tried pthread_start(), but its very likely to be equal to (1), is it not? 3) Carbon's LSOpenApplication is neither daemon-safe, nor does it allow to execute as a specific user (or root, so I could setuid() myself). 4) Using launchd() works great: launch_data_t msg = launch_data_alloc(LAUNCH_DATA_DICTIONARY); launch_data_dict_insert(msg,launch_data_new_string("com.c.App"), LAUNCH_KEY_STARTJOB); launch_data_t resp = launch_msg(msg); but I am missing an interface to set the user. Of course a fixed user can be chosen in the plist, but then its not dynamic. Also, I can start an app as root with launchd and setuid from within this app, but if someone exchanges the app, he will gain root access. Am I missing something in the launchd API interface? How would one typically write an ftp-daemon on Mac OS (i.e. write a daemon that runs as root, then spawns a child that runs as the user that requests ftp login)? Cheers, Mario _______________________________________________ Do not post admin requests to the list. They will be ignored. Darwin-dev mailing list (Darwin-dev(a)lists.apple.com) Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/darwin-dev/site_archiver%40lists.app… This email sent to site_archiver(a)lists.apple.com

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Re: launchd wrong behavior for nonexistent paths and crashed services
by Stéphane Sudre 25 Sep '08

25 Sep '08

site_archiver(a)lists.apple.com Delivered-To: darwin-dev(a)lists.apple.com On Sep 24, 2008, at 7:49 PM, Kevin Van Vechten wrote: On Sep 24, 2008, at 2:11 PM, Terry Lambert wrote: The bug report has been reported as a duplicate. Being pessimistic, I guess it means it will never be fixed in 10.5. _______________________________________________ Do not post admin requests to the list. They will be ignored. Darwin-dev mailing list (Darwin-dev(a)lists.apple.com) Help/Unsubscribe/Update your Subscription: http://lists.apple.com/mailman/options/darwin-dev/site_archiver%40lists.app… Using the SuccessfulExit condition is useful in cases like this. If InternetSharing sees there's nothing to do, and exits successfully, the job wont' be restarted until another condition is met. Please file a radar on this specific issue. Please file a bug against interface disabling not automatically disabling Internet sharing via the interface being disabled. This email sent to site_archiver(a)lists.apple.com

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