So I am trying to keep my Node server on a embedded computer running when it is out in the field. This lead me to leveraging inittab's respawn action. Here is the file I added to inittab:
node:5:respawn:node /path/to/node/files &
I know for a fact that when I startup this node application from command line, it does not get to the bottom of the main body and console.log "done" until a good 2-3 seconds after I issue the command.
So I feel like in that 2-3 second window the OS just keeps firing off respawns of the node app. I see in the error logs too in fact that the kernel ends up killing off a bunch of node processes because its running out of memory and stuff... plus I do get the 'node' process respawning too fast will suspend for 5 minutes message too.
I tried wrapping this in a script, dint work. I know I can use crontab but thats every minute... am I doing something wrong? or should I have a different approach all together?
Any and all advice is welcome!
TIA
Surely too late for you, but in case someone else finds such a problem: try removing the & from the command invocation.
What happens is that when the command goes to the background (thanks to the &), the parent (init) sees that it exited, and respawns it. Result: a storm of new instantations of your command.
Worse, you mention embedded, so I guess you are using busybox, whose init won't rate-limit the respawning - as would other implementations. So the respawning will only end when the system is out of memory.
inittab is overkill for this. I found out what I need is a process monitor. I found one that is lightweight and effective; it has some good reports of working great out in the field. http://en.wikipedia.org/wiki/Process_control_daemon
Using this would entail configuring this daemon to start and monitor your Node.js application for you.
That is a solution that works from the OS side.
Another way to do it is as follows. So if you are trying to keep Node.js running like I was, there are several modules written meant to keep other Node.js apps running. To mention a couple there are forever and respawn. I chose to use respawn.
This method entails starting one app written in Node.js that uses the respawn module to start and monitor the actual Node.js app you were interested in keeping running anyway.
Of course the downside of this is that if the Node.js engine (V8) goes down altogether then both your monitoring and monitored process will go down with it :-(. But its better than nothing!
PCD would be the ideal option. It would go down probably only if the OS goes down, and if the OS goes down then hope fully one has a watchdog in place to reboot the device/hardware.
Niko
Related
My goal is to write to a file (that the user whenever the user launches an application, such as FireFox) and timestamp the event.
The tricky part is having to do this from the kernel (or a module loaded onto the kernel).
From the research I've done so far (sources listed below), the execve system call seemed the most viable. As it had the filename of the process it was handling which seemed like gold at the time, but I quickly learned that it wasn't as useful as I thought since this system call isn't limited to user-related operations.
So then I thought of using ps -ef as it listed all the current running processes and I would just have to filter through which ones were applications opened by the user.
But the issue with that method is that I would have to poll every X seconds so, it has the potential to miss something if the user launched and closed an application within the time that I didn't call ps -ef.
I've also realized that writing to a file would be a challenge as well, since you don't have access to the standard library from the kernel. So my guess for that would be making use of proc somehow to allow the user to actually access the information that I'm trying to log.
Basically I'm running out of leads and I'd greatly appreciate it if anyone could point me in the right direction.
Thanks.
Sources:
http://tldp.org/LDP/lkmpg/2.6/html/x978.html (not very recent)
https://0xax.gitbooks.io/linux-insides/content/SysCall/syscall-4.html
First, writing to a file or reading a real file from the kernel is a bad idea which is not used in the kernel. There is of course VFS files, like /sys/fs or /proc, but this is a special case and this is allowed.
See this article in Linux Journal,
"Driving Me Nuts - Things You Never Should Do in the Kernel" by Greg Kroach-Hrtman
http://www.linuxjournal.com/article/8110
Every new process that is created in Linux, adds an entry under /proc,
as /proc/pidNum, where pidNum is the Process ID of the new process.
You can find out the name of the new application which was invoked simply by
cat /proc/pidNum/cmdline.
So for example, if your crond daemon has pid 1336, then
$cat /proc/1336/cmdline
will give
cron
And there are ways to monitor adding entries to a folder in Linux.
My program checks if there is a new version of itself. If yes it would exit and start an updater that replaces it and then restarts.
My problem is that I haven't found any info on how to make process start right after closing the actual program.
Any suggestions?
Thanks in advance
I intended to add a comment, but I'm too low in points here. The updater itself should probably contain a check to determine whether your application is running an instance, and it should contain a timeout loop that performs this check and factor the timeout following it's startup state. That way you can awaken it, and close your application. The updater should just determine your application is not running, compare versions perform the intended update operation.
a possible solution would also be to create a task via tash sceduler or cron job, starting an out of process application, like CMD.exe.. which brings me to my original comment-question: in regards to what Operating System(s) and Platform(s) is your program intended for?
I'm looking for a way to run a program when locking the screen in Fedora 15 (linux). Basically I want to start running a motion detection program when the screen locks, or I manually hit Ctrl+Alt+L, but I don't know what commands are being run or where to alias my own intermediate step in. I assume it's:
gnome-screensaver-command --lock
but am not sure how to go about this. Anybody know how, or a direction to start looking in?
Edit, since link was in a comment:
This is done with dbus-monitor and described here.
The dbus system advertises screen locking; monitor for ActiveChanged on org.gnome.ScreenSaver. (see http://people.gnome.org/~mccann/gnome-screensaver/docs/gnome-screensaver.html )
e.g. (word-wrapped for clarity)
signal sender=:1.68 -> dest=(null destination)
serial=53 path=/org/gnome/ScreenSaver;
interface=org.gnome.ScreenSaver; member=ActiveChanged
boolean true
Unfortunately, this will require writing more code than just a shell script, I'm afraid; although I'd be curious if you could ask dbus to call your program as a handler for that signal, somehow; otherwise, I suppose you'd just start a daemon process and listen for that signal to be broadcast…
I have a Window Forms application (using clickonce installation, running on a terminal server) that occasionaly ends up with a thread that appears to be running in a tight loop. The user doesn't know this happens as the app continues to run as expected. Also I have determined that I can kill the problem thread without any apparent affect on the app.
I can use Process Explorer to find the instance of an app with the problem and can isolate the thread with the problem but haven't found any way to look into the thread to find anything that would help me determine what is causing the problem. Does anyone know of a way to some additional information about a thread, like maybe strings, that would help me zero in on the issue?
Thanks,
Dave
Haven't tried this myself but "Process Monitor" claims it "shows real-time file system, Registry and process/thread activity"
http://technet.microsoft.com/en-us/sysinternals/bb896645.aspx
Hope this helps.
You should be able to attach Visual Studio to the running process to get more information. Provided the .pdb files are included with the application and you have source code for the avialable version you should be able to use the Threads window combined with pausing / stepping through to see just what the code is doing.
Every morning when I get into work I launch about a dozen apps and whatnot (FF, TB, VSx2-3, Eclipse, SSH, SVN update x2-3). Needles to say this does a good job of warming up my HDD for the day. I rather suspect that it would run a lot faster if they were launched sequentially (not to mention that I wouldn't need to click in 17 different places).
Is there a preexisting product that can kick off a sequence of tasks/apps/etc. where each task is only started after the last app is done hammering the HDD?
It would nerd to be able to kick apps like VS and firefox and also be able to trigger explorer context menu items like SVN update in TortoiseSVN.
Try SlickRun, it's free, I've used it for years, I use it constantly and I'd be lost without it.
Think of it like a configurable Start->Run command, it'll do what you want (you can configure n second pauses between multiple commands), and if you install it you'll use it for a thousand different things before the first week is out.
P.S. I have no stake in SlickRun, I just like it :)
Unfortunately, I don't know of any software that can do this for you automatically.
However, can't you trigger the updates through a console SVN task? If so, can't this be done by creating a batch file? It's low tech, and you might want to add a few pauses between each task, but it should do what you want.
As you mention TortoiseSVN, I'll assume your O/S is windows.
You could launch an Autohotkey script at startup. I don't think it can easily detect HDD activity, but you can at least wait until each window appears with the WinWaitActive command.
If each application has an average time they take to complete, you could simply use Windows' Scheduled Tasks application. Obviously you'll need to be running Windows but Scheduled Tasks can be found in the Control Panel.
Execute "Add Schedules Task", select the program, the frequency and then the specific time.