I'm working on a software that I must add some new features on it. Its on Linux and runs on the terminal.
What I want to know is how can I find out all the files that being used when I run a certain command.
Note that The application is so large has a lot of files for different daemons. I'm concerned about one daemon and I want to know what files from the app are responsible about running this daemon.
Anyone have a clue about this ?
Thanks
Related
I am developing an Linux application using Python3. This application synchronizes the user's file with the cloud. The file are in a specific folder. I want that a process or daemon should run in background and whenever there is a change in that folder, It should start synchronization process.
I have made modules in Python3 for synchronization but I don't know that How to run a process in background which should automatically detect the changes in that folder? This process should always run in background and should be started automatically after boot.
You have actually asked two distinct questions. Both have simple answers and plenty of good resources online, so I'm assuming you simply did not know what to look for.
Running a process in the background is called "daemonization". Search for "writing a daemon in python". This is a standard technique for all Posix based systems.
Monitoring a directory for changes is done through an API set called inotify. This is Linux specific, as each OS has its own solution.
I have a script to start and stop my services. My server is based on Linux. How do I automate the process such that when OS is shutdown the stop script runs and when it is starting up, the start script runs?
You should install init script for your program. The standard way is to follow Linux Standards Base section 20 subsections 2-8
The idea is to create a script that will start your application when called with argument start, stop it when called with argument stop, restart it when called with argument restart and make it reload configuration when called with argument reload. This script should be installed in /etc/init.d and linked in various /etc/rd.* directories. The standard describes a comment to put at the beginning of the script and a uitlity to handle the installation.
Please, refer to the documentation; it is to complicated to explain everything in sufficient detail here.
Now that way should be supported by all Linux distribution. But Linux community is currently searching for better init system and there are two new, improved, systems being used:
systemd is what most of the world seems to be going to
upstart is a solution Ubuntu created and sticks to so far
They provide some better options like ability to restart your application when it fails, but your script will then be specific to the chosen system.
I want to create an application that runs in the background in Linux (daemon) that will basically at set times (5 times) play a music file or any sound given every single day. I want this daemon to start when the computer is started in terminal mode (non-GUI). I want to know if this is possible and if so, What considerations, tools, and programming language would be the most efficient in doing so? This will be a dedicated computer that will only be executing this task, so if any recommendations on how I can maximize efficiency while disabling other features that are not required for this task will be appreciated. Also, could you please explain how processes and tasks work in terminal (non-GUI)? I always thought terminal was something like CMD in Windows and can only run tasks one at a time.
EDIT: I need the sound to run at variable times, I'll be fetching these times from a website. Any suggestions regarding how to achieve this?
Thanks for the help and sorry for any shortcoming in the questions or my research.
Look at using cron to run your tasks. cron is a very flexible scheduling utility built in to most Linux distributions.
Basically, with cron you specify a task to run (your main program, or maybe just a sound-playing program), all of its arguments, and when it runs. cron takes care of running it, and will even send you "mail" if the job produces any output (such as errors).
You can make processes fork into a subprocess of your terminal, i.e. you are able to run more than one task at a time by putting a & after your terminal command:
> cmd&
> [you can type other commands here but the "cmd" program is still running]
However, for services you generally don't have to worry about starting it as a subprocess because the system already knows to do this. Here's a good question from Super User that has an example of a working service. Simply place your service as a shell script in the /etc/init.d and it will be automatically started as a service.
I have a linux service (c++, with lots of loadable modules, basically .so files picked up at runtime) which from time to time crashes ... I would like to get behind this crash and investigate it, however at the moment I have no clue how to proceed. So, I'd like to ask you the following:
If a linux service crashes where is the "core" file created? I have set ulimit -c 102400, this should be enough, however I cannot find the core files anywhere :(.
Are there any linux logs that track services? The services' own log obviously is not telling me that I'm going to crash right now...
Might be that one of the modules is crashing ... however I cannot tell which one. I cannot even tell which modules are loaded. Do you know how to show in linux which modules a service is using?
Any other hints you might have in debugging a linux service?
Thanks
f-
Under Linux, processes which switch user ID, get their core files disabled for security reasons. This is because they often do things like reading privileged files (think /etc/shadow) and a core file could contain sensitive information.
To enable core dumping on processes which have switched user ID, you can use prctl with PR_SET_DUMPABLE.
Core files are normally dumped in the current working directory - if that is not writable by the current user, then it will fail. Ensure that the process's current working directory is writable.
0) Get a staging environment which mimics production as close as possible. Reproduce problem there.
1) You can attach to a running process using gdb -a (need a debug build of course)
2) Make sure the ulimit is what you think it is (output ulimit to a file from the shell script
which runs your service right before starting it). Usually you need to set ulimit in /etc/profile file; set it ulimit -c 0 for unlimited
3) Find the core file using find / -name \*core\* -print or similar
4) I think gdb will give you the list of loaded shared objects (.so) when you attach to the process.
5) Add more logging to your service
Good luck!
Your first order of business should be getting a core file. See if this answer applies.
Second, you should run your server under Valgrind, and fix any errors it finds.
Reproducing the crash when running under GDB (as MK suggested) is possible, but somewhat unlilkely: bugs tend to hide when you are looking for them, and the debugger may affect timing (especially if your server is multi-threaded).
Sorry about the really ambiguous question, I really have no idea how to word it though hopefully I can give you more detail here.
I am developing a project where a user can log into a website and book a server to run a game for a specific amount of time. When the time is up the server stops running and the players on the server are kicked off. The website part is not a problem, I am doing this in PHP and everything works. It has a calendar system to book a server and can generate config files based on what the user wants.
My question is what should I use to run the specific game server on the linux box with those config files at the correct time? I have got this working with bash scripts and cron, but it seems very un-elegant. It literally uses FTP to connect to the website so it can download all the necessary config files and put them in a folder for that game and time. I was wondering if there was a better way of doing this. Perhaps writing a program in C, but I am not sure how to go about doing this.
(I am not asking for someone to hold my hand and tell me "write this code here", just some ideas of a better way of approaching this problem)
Thanks so much guys!
Edit: The webserver is a totaly different machine. I would theoreticaly like to have more than one game server where each of them "connects" (at the moment FTP) to the webserver, gets a file saying what it has to do at a specific time and downloads any associated files then disconnects.
I think at is better suited for running one time jobs than cron.
For a better approach for the downloading files etc, you should give more details on your setup (like, the website and the game server, are they on the same machine? Or the same network? etc etc.
You need a distributed task scheduler. With that, you can:
Schedule command "X" to be run at a certain time.
Specify the machine (or ask it to pick a machine from a pool of available machines)
Webserver would send request to this scheduler via command line or via web service when user selects a game server and a time.
You can have a look at : http://www.acelet.com/super/SuperWatchdog/index.html
EDIT :
One more option :http://jobscheduler.sourceforge.net/