In Linux, I want a process to be assigned with higher priority than usual. I.e. when a process starts I want it's priority to be set to higher value. I want this to be done implicitly, i.e when the process starts (eg.:on a double click).
For this will I have to change the kernel code (sched.c)?
And are there any tools or packages using which I can see how exactly a process starts and how the priorities are assigned?
Would ptrace ( http://linux.die.net/man/2/ptrace) and strace ( http://linux.die.net/man/1/strace) help me with this?
Assuming you don't want to hack the actual application itself you can always create a custom desktop file which wraps the command with "nice" which will modify the niceness (priority) of the command you'll run.
For example, create a ~/.local/share/applications/myfastapp.desktop which looks like:
[Desktop Entry]
Encoding=UTF-8
Version=1.0
Type=Application
Exec=nice -n -20 /usr/bin/myapp
Name=My App (niced)
Comment=Custom definition for myapp
Have the process call the set_priority() system call in main() to lower it's nice level and raise it's priority. See the man page for details: http://linux.die.net/man/2/setpriority
You can also mark the process as a real time process using sched_setscheduler() but that is a little bit more involved and probably an overkill for what you seek.
You 100% don't need to change the kernel for this :-)
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 writing a command line application in Mac using Objective-c
At the start of the application, i want to check if another instance of the same application is already running. If it is, then i should be either wait for it to finish or exit the current instance or quit the other instance etc.
Is there any way of doing this?
The standard Unix solution for this is to create a "run file". When you start up, you try to create that file and write your pid to it if it doesn't exist; if it does exist, read the pid out of it, and if there's a running program with that pid and your process name, wait/exit/whatever.
The question is, where do you put that file, and what do you call it?
Well, first, you have to decide what exactly "already running" means. Obviously not "anywhere in the world", but it could be anything from "anywhere on the current machine" to "in the current desktop session". (For example, if User A starts your program, pauses it, then User B comes along and takes over the computer via Fast User Switching, should she be able to run the program, or not?)
For pretty much any reasonable answer to that question, there's an obvious pathname pattern. For example, on a Mac, /tmp is shared system-wide, while $TMPDIR is specific to a given session, so, e.g., /tmp/${ARGV[0]}.pid is a good way to say "only one copy on the machine, period", while ${TMPDIR}/${ARGV[0]}.pid is a good way to say "only one copy per session".
Simple but common way to do this is to check the process list for the name of your executable.
ps - A | grep <your executable name>
Thank you #abarnert.
This is how I have presently implemented. At the start of the main(), I would check if a file named .lock exists in the binary's own directory (I am considering moving it to /tmp). If it is, application exits.
If not, it would create the file.
At the end of the application, the .lock file is removed
I haven't yet written the pid to that file, but I will when exiting the previous instance is required (as of yet I don't need it, but may in the future).
I think PID can be retrieved using
int myPID=[[NSProcessInfo processInfo] processIdentifier];
The program will be invoked by a custom scheduler which is running as a root daemon. So it would be run as root.
Seeing the answers, I would assume that there is no direct method of solving the problem.
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've found this question, but even when is close to what I need, is useless
Basically, I have an app that needs to do something when another process (of known name) is launched and/or terminated, but i don't have the PID, so i can't set a kqueue to look for it.
I could do a while for "ps aux | grep processtolook | grep -v grep" command, but that's my last resort.
Any ideas?
Look at this answer: Determine Process Info Programmatically in Darwin/OSX. The libproc.h header file has proc_listpids which will get you all the pids. You can then get the pid information in a loop and using proc_pidinfo and check the name. Looking at the top source as suggested there might also be worthwhile. (The current verson is here http://www.opensource.apple.com/source/top/top-67/.)
Unfortunately, this is an undocumented interface and subject to change at any time. Also, it isn't the quickest thing, since you have to loop over all the processes in the system. In general, this isn't a great way to do this.
A better way might be to write a new processtolook that simply invoked the old one which you can move or rename. It could then notify you of the process start and stop. Is that a possibility?
If the target process/program name which you want the PID is "processtolook" then you can use pidof command to get the PID of that running program.
pidof processtolook
have a look at the pidof manual. This is a part of sysvinit-tools package.
EDIT1:
Have a look at this code i found: http://programming-in-linux.blogspot.com/2008/03/get-process-id-by-name-in-c.html
This might help you get you the outline.
On BSD you can use kvm_openfiles and kvm_getprocs to implement what you want. I don't know if it's available on OSX. If you have a pgrep program, look how it's implemented (src/bin/pkill.c).