I am creating a cross-platform app and would like to write some information to a log file. I know that I can dump it on the desktop or any number of unexpected places, but I am interested in placing it in the place where each operating system recommends. To complicate matters, systemd may be present and change expectations based on the platform.
Where is the expected place for Linux? And are there any other expectations I should be aware of (like if I need to put it in a folder with my company or app name)?
Related
The problem is that I need to share files between 2 programs, but I don't want that those files are accessible by the user of the computer and other programs than these 2. So the flow of the files are like this: Program A (which I will code myself) recieves a file from the internet and puts somewhere on the computer. Then Program A calls Program B (which I didn't code and can't change). Program B reads the downloaded file and does some things with it and produces another file which Program B puts also somewhere on the computer. Then Program A reads that file and uploads it to the internet.
What I have found
I thought that maybe Windows Sandbox was interesting, but the problem with Windows Sandbox is that it's only available to windows 10 pro and windows 11, and that it is virtualised, and performance is quite important for Program B... So any virtualised software is not very usable, unless it is close to native performance.
For Linux, I found FreeBSD jails. But this seems more focussed on keeping the applications in the jail prohibited to access files outside the jail than to prohibit the programs outside the jail from reading and writing to files in the jail. So actually I need the opposite...
Another interesting concept was to keep the files stored in RAM like mmap in Linux, but since I can't change Program B, I don't know how to implement that. Is there some kind of container application that encapsulates the IO of Program B and redirects it to a file in RAM?
Does anyone have some suggestions? Thanks!
You can't really prevent the user/owner of the computer from reading the file if you are storing it on their disk. You can try to make it more difficult to access the content (which is what DRM does) but ultimately you the user can always bypass your controls given sufficient motivation and resources. Even if you store the files purely in RAM, a user with administrative permissions can dump your program's memory, and extract the files from there.
Are the settings or configuration specifics of a printer on a *nix system using CUPS stored in a file? My assumption is yes, as *nix systems seem to use files for everything as opposed to using a registry system as does Windows. If so, where are such files located? Are they capable of having their file permissions modified, and if so, what could cause such a thing to occur in a non-manual way?
This question relates to one of my other questions in helping to explore a single, individual theory toward an answer there, but is decidedly separate.
Check on /etc/cups, for printers the file is printers.conf.
They can have permissions modified since they usually belong to the lp group, not a single user. Check cron jobs, system updates and any other cups interface that your distribution provides.
Coming from Windows background here.
Is it an acceptable practice for GUI Linux applications to store their data files (not user-specific) at hard-coded locations (e. g. /etc/myapp/stuff)? I couldn't find any syscalls that would return the preferred directory for app data. Is there a convention out there as to what goes where?
/opt/appname/stuff according to the Linux Filesystem Hierarchy Standard
Your distribution's packaging system likely provides ways to handle common installation paths. What distribution are you using?
Generally speaking, yes there is a convention. On most Linux systems, application configuration files are typically located at /etc/appname/. You'll want to consult the LSB (Linux Standard Base) and the Linux FHS (Filesystem Hierarchy Standard) for their respective recommendations.
Also, if you are targeting your application towards a specific Linux distro, then that distro vendor probably has their own specific recommendations as far as packaging and related-conventions are concerned. You'll want to look at your distro vendor's developer pages for more information.
Configuration files for processes with elevated privileges are generally stored in /etc. Data files for processes with elevated privileges (Web Server, Mail Server, Chat Server, etc.) are generally stored in /var. And that's where consistency ends. Some folks say you start with the location to store them (/etc|/var) then have an appname sub-folder for your app, then continue from there as necessary.
If you're not a system daemon with elevated privileges, your only consistent choice is a dot directory in the launching user's home directory. I think the Free Desktop Standards (XDG) specify ~/.config for per-user configuration, and ~/.cache for replaceable static and/or generated data you need to save.
Looking at my Home Directory, a few key dot directories I have are:
~/.cache
~/.config
~/.irssi
~/.maildir
~/.mozilla
~/.kde
~/.ssh
~/.vnc
[edit]
While not a syscall, the XDG specifications I reference are at http://standards.freedesktop.org/basedir-spec/basedir-spec-latest.html
There are certain conventions.
System-wide, readable/editable (text-based) configuration files go in /etc/appname/.
System-wide, per-machine binary data files that change (eg. binary databases) go in /var/*/appname/ - /var/cache/appname/, /var/spool/appname/ and /var/lib/appname/ are the most common.
System-wide binary data files that could notionally be shared between machines (eg. things like graphics and sound files) go in /usr/share/appname/.
The full paths that Unix/Linux/GNU applications use to store config files and other data is usually set when an application is configured prior to compilation. These paths then get hard-coded into the compiled binary (you can see examples of this by running strings(1) over some existing executables).
That is, these types of paths are build-time configurable, not run-time configurable by default. Many apps will support command line options to specify where a configuration file is, and that configuration file will usually contain paths for other application resources. This allows an application to run with minimal configuration (built-in paths) but also allows a site to customise the paths completely.
Under Linux, only the basic services (opening a file, doing networking and interprocess communication etc) are provided as system calls. The rest is done using libraries.
If you are coding a GUI application, you should look into your toolkit's documentation to see if it provides a mechanism for managing defaults. Both KDE and Gnome have one for instance.
For some unfortunate reasons, I have to convert a proprietary and binary library from a one-user per workstation to a multi-user per workstation setup.
Current setup. A user uses a program linked against a library. This library reads a system wide configuration file (using an hard-coded path, ie /usr/local/thelib/main.conf ) which itself contains several paths to several working directories. The wdir are themselves containing a bunch of user data files.
Desired outcome. Being able to manage several users on the same workstation. Of course, a user shall not be able to read nor alter any other user's data through the library, which should be taken care of by unix rights if I manage to feed the library a different working directory for each user.
The library might be used by several users at the same time so ln-ing the configuration file in /usr/local at runtime is not an option.
I was thinking of using FUSE in order to provide a different content for the file /usr/local/thelib/main.conf, depending on an environnement variable or the current unix user. The environnement var would then be used as a switch inside the code producing the configuration file.
I'm confortable using Python, Perl or C.
The workstation is running an up-to-date GNU/Linux Debian or Ubuntu distribution with a pretty recent kernel.
So. What do you think :
would you use FUSE ?
would you produce another kind of wrapper - using chroot(2) was suggested below per janneb - ?
use something else allowed by Linux ?
I kinda know that I would be able to produce something functional but I'll get the community advice since I don't want to reinvent the wheel right now.
Thanks.
Florian
you could use LD_PRELOAD to load a small stub that intercepts open() calls, and opens ~/.main.conf (assuming this is a shared object). Then in your application startup routine, check that LD_PRELOAD is set to the correct value, and if not, restart the app with the correct environment.
A simple way would be for the app to call chroot() before calling the library init function(s). E.g. if you chroot into $HOME/theapp then each user can have a private own config file in $HOME/theapp/usr/local/thelib/main.conf as well as private working dirs somewhere under $HOME/theapp.
I posted this question a while ago regarding where to store non-user specific application data on Linux.
As you can see, I intended to use "/Library/Application Support” on Mac and perhaps "/var/lib" or "/usr/share" on Linux.
On an existing application (currently Windows only) we use “\ProgramData” on Vista & Windows 7 and “\Documents and Settings\All Users“ on Windows XP (both obtained using System.getenv("ALLUSERSPROFILE"), which does not work on Mac or Linux).
The problem I am finding with the Mac & Linux locations (unlike the Windows ones) is that they are not accessible by non-root/admin users, which sort of defeats the purpose of using them.
What is the best practice is this case? We could simply store the application data in the user's home directory. I wouldn't actually be dead against this, as it seems reasonable for the application to appear completely 'new' when a new user tries using it. The main problem this gives us is that each user would have to enter the serial number in order to activate the application (the activation info is part of the 'application data' we need to store). This isn't really ideal.
That said, if there is no real alternative then I suppose it will have to do.
What do you mean by non-user specific application data?
Read-only resources needed by application, such as localization strings or button icons:
on Mac they are stored in application bundle itself, in Resources subfolder
on Linux, they can be stored near application binary, in /opt/<app>/etc for instance.
Read/write properties, such as serial number:
you can consider this information as user-specific application data, so it should go somewhere in $HOME directory
you can consider this information as computer-wide application data, in which case its setting should be perfomed during software installation process, i.e., with administrative privileges.
/Users/Shared/ is writable for everyone. That said, if you need to support computer-wide licenses, the best place for serial numbers, IMHO, is indeed /Library/Application Support. You would have to use Authorization Services once to ask for an admin password and save the serial number there. If a user fails to enter the admin password, save the serial number in ~/Library/Application Support instead.