Axel,
Thanks for the feedback. I apologize profusely for the delay in my
response; I just had too many fires to deal with to give this the
attention it needed.
Axel Luttgens <mailto:axel.luttg...@skynet.be>
June 25, 2015 at 5:20 AM
Le 23 juin 2015 à 03:31, James Bucanek a écrit :
Greetings,
Here's my problem in a nutshell:
I have a simple scheduler daemon that runs in the background for logged in
users. The problem is that it won’t start when installed in Yosemite (seems to
start in all previous versions of OS X that use launchd).
Hello James,
If you allow, some questions for better understanding your context.
Here’s what my program does:
Which program? Some kind of installer?
More generally, could you describe what exactly you want to achieve, the
workflow you are considering? We could then proceed with some trials at home.
;-)
I'm the author of QRecall (www.qrecall.com). It's a backup and archiving
solution. The feature of interest to this discussion is the installation
of a light-weight scheduler daemon that manages the automated execution
of background tasks (backups, maintenance, validity checks, and so on).
The scheduler daemon can be installed in one of two ways. Most users
install the scheduler as a regular user agent. The scheduler runs only
when the user is logged in, and that satisfies 90% of my user base. I
have had no problems installing, or uninstalling, the scheduler as a
per-user agent on any version of OS X.
However, my program also offers the ability to run scheduled tasks when
the user is logged out. (In fact, you can even schedule an action to
start when you log in or out.) For this to work, the scheduler
(obviously), has to run all the time. For that, I install the scheduler
as a system-wide agent, instead of a per-user agent. I then employ a
little trick to make sure the scheduler runs all the time. (See sidebar.)
-- Begin Sidebar --
The installation and running of the scheduler process as a per-user
daemon is a bit involved. So for completeness, I've include a brief
explanation of what's going on, although it shouldn't have any bering on
the issue at hand. So feel free to skip this sidebar, if you're so
inclined. Or, dig into it, if you think this is where the problem is.
I only run processes as root when absolutely necessary. The scheduler
doesn't need to run as root; it needs to run as a regular user, and just
for those users with QRecall installed. This is the area where there's a
little impedance mismatch between QRecall and OS X.
OS X has the concept of a user agent, a system-wide agent, and a system
daemon. What is doesn't have is the concept of a "user daemon": a
process that runs, for a single user, as that user, and runs all the
time, whether the user is logged in or not.
A long time ago, I posed this problem to the list and got a great
suggestion (I think it was from Jim Luther) that has served me well for
years:
(1) Install the scheduler as a system-wide agent. OS X will, by default,
start a per-user instance of the process for every user that logs in.
(2) Have a global configuration file with a list of UIDs that should be
running the scheduler all the time. When each per-user instance is
started launchd, the scheduler simply consults the list. If it's current
UID is on the list, it runs normally. If it isn't on the list, it
terminates with a non-zero exit code.
(3) Install a system daemon (QRecallKicker). This daemon runs as root
and reads the same global list of UIDs. It forks a copy of itself for
each UID on the list. Each copy switches to running as that UID (which
it can, 'cause it's root), and then does something that will cause OS X
to need the bootstrap for that UID. I make a single call to
bootstrap_look_up() for a non-existent service. The side effect is that
OS X lazily creates the bootstrap for that UID. As part of the bootstrap
creation, launchd starts the system-wide agents for that user.
The end result is this: When the system starts up, the QRecallKicker
daemon "kicks" each of the users that should be running the "always on"
version of the scheduler. This creates a bootstrap for that user and
starts its instance of the scheduler agent. If any other users log in,
their per-user instance of the scheduler is started, and immediately
terminates because that user isn't on the list.
Once a bootstrap is created, it stay created until OS X restarts. So
even if the user logs out, the scheduler continues running.
So that's the tortured story of why I install the scheduler as a
system-wide agent.
-- End Sidebar --
1) I install the com.qrecall.sheduler.plist in /Library/LaunchAgents/ (with the
correct ownership and access privileges).
So, do you install the plist yourself, beforehand, or is this done by aforementioned
"program"?
Could you show us that plist?
Here's the plist:
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN"
"http://www.apple.com/DTDs/PropertyList-1.0.dtd";>
<plist version="1.0">
<dict>
<key>KeepAlive</key>
<dict>
<key>SuccessfulExit</key>
<true/>
</dict>
<key>Label</key>
<string>com.qrecall.scheduler</string>
<key>LimitLoadToSessionType</key>
<string>Background</string>
<key>ProgramArguments</key>
<array>
<string>/Library/Application Support/QRecall/QRecallScheduler</string>
</array>
<key>RunAtLoad</key>
<true/>
</dict>
</plist>
2) launchctl load -S Background
/Library/LaunchAgents/com.qrecall.scheduler.plist
(successful)
I guess this is done by the "program".
Is it run by a logged in user (in the GUI) and running as that user?
Here's how the installation of the system-wide agent is accomplished:
(1) A privileged helper service has already been installed via SMJobBless().
(2) When the scheduler needs to be installed this way, the helper
service is run (as root) with instructions to install the scheduler. The
helper then:
(2)(a) Creates a .plist for the agent and copies it to
/Library/LaunchAgents/com.qrecall.scheduler.plist, assigning it the
correct ownership (root) and permissions (-rw-r--r--) required by launchd.
(2)(b) Runs the command 'launchctl load -S Background
/Library/LaunchAgents/com.qrecall.scheduler.plist' as root.
(I've always wondered if I should rewrite these steps to use
SMJobSubmit, but I now see that it's already deprecated.)
Note that this only happens when the scheduler needs to be installed in
it's "daemon" version. Installation and removal of the per-user
scheduler agent is handled entirely in userland by the main app.
In the past (pre-10.10), this has always installed and started the agent
process immediately.
3) launchctl start com.qrecall.scheduler
(exits with status 1)
And the scheduler process is NOT started. All attempts to get it started
through launchctl have failed.
However, I know that it’s installed because if you simply restart the system
the scheduler deamon starts running like a champ.
For any user that logs in?
Or for a specific user only?
The scheduler is only going to start for the user's it's configured to
run for. Having said that, it doesn't appear to start for any user when
the 'launchctl load' command is issued. Although, as I've mentioned
before, if you restart the system and log back in, it starts and runs
just fine.
I hope that this more clearly explains what I'm trying to accomplish.
Actually, I've already accomplished it; this has been working for years
but now seems (slightly) broken in 10.10 and 10.11.
If the solution is to use the new launchctl command syntax, I'll jump
right on it ... just as soon as someone can help me understand what
command I should be issuing.
I've left the original message attached, since it's been so long since I
posted it.
Thanks again, in advance, for all the help and ideas.
James Bucanek
James Bucanek <mailto:subscri...@gloaming.com>
June 22, 2015 at 6:31 PM
Greetings,
Here's my problem in a nutshell:
I have a simple scheduler daemon that runs in the background for
logged in users. The problem is that it won't start when installed in
Yosemite (seems to start in all previous versions of OS X that use
launchd).
Here's what my program does:
1) I install the com.qrecall.sheduler.plist in /Library/LaunchAgents/
(with the correct ownership and access privileges).
2) launchctl load -S Background
/Library/LaunchAgents/com.qrecall.scheduler.plist
(successful)
3) launchctl start com.qrecall.scheduler
(exits with status 1)
And the scheduler process is NOT started. All attempts to get it
started through launchctl have failed.
However, I know that it's installed because if you simply restart the
system the scheduler deamon starts running like a champ.
Now ... I know what you're going to say: "Dude! You should be using
the new launchctl commands introduced in 10.10!"
Tried that. I can't seem to get anywhere with it. Basically, I don't
know what I'm doing. I've read the man page for the new launchctl
about 20 times and I'm still not sure how I should be using it.
For per-user agents, it seems pretty obvious that you would bootstrap
and address the service in the user/login/gui domain (i.e. launchctl
enable user/501/com.qrecall.scheduler).
But I don't understand how to treat a system-wide user agent that
should be installed in /Library/LaunchAgents. Through trial and error,
I've discovered that I can address the current user's instance of the
scheduler process for commands like "kill". So this command works:
launchctl kill TERM user/501/com.qrecall.scheduler
It sends a TERM signal and the daemon restarts.
However, I can't find anyway to use the bootstrap command to install
it, the enable command won't start it, and the kickstart command says
there's no such service.
It would seem to make sense that a system-wide agent would have to be
installed in the system domain, but this command:
sudo launchctl bootstrap system
/Library/LaunchAgents/com.qrecall.scheduler
results in the error
"/Library/LaunchAgents/com.qrecall.scheduler.plist: Service cannot
load in requested session"
Attempts to use any other domain in the command result in a syntax
error, so I'm completely stumped as to how the service should be
installed.
I've figured out the I can enable and disable the per-user instance,
but it has no effect on the running process. In other words, disabling
won't halt the service and enabling it won't start it.
And don't get me started on unbootstrap, which doesn't appear to be
implemented.
So, at this point I have my feet planted firmly in mid-air...
James Bucanek
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