Location of ini/config files in linux/unix?

Two questions, really:

1. Is there a standard/convention regarding the placement on configuration files?

   For system or quasi-system programs they seem to usually be somewhere in /etc. It seems less clear for plain application programs or programs with insufficient privileges for /etc.

2. In processing program options is there a standard hierarchy of what takes precedence? E.g. does a command line option override an initialization file and/or an environment variable? Vice versa? Or is this entirely up to the developer?

Solution 1:

You should adhere your application to the XDG Base Directory Specification. Most answers here are either obsolete or wrong.

Your application should store and load data and configuration files to/from the directories pointed by the following environment variables:

• $XDG_DATA_HOME (default: "$HOME/.local/share"): user-specific data files.
• $XDG_CONFIG_HOME (default: "$HOME/.config"): user-specific configuration files.
• $XDG_DATA_DIRS (default: "/usr/local/share/:/usr/share/"): precedence-ordered set of system data directories.
• $XDG_CONFIG_DIRS (default: "/etc/xdg"): precedence-ordered set of system configuration directories.
• $XDG_CACHE_HOME (default: "$HOME/.cache"): user-specific non-essential data files.

You should first determine if the file in question is:

1. A configuration file ($XDG_CONFIG_HOME:$XDG_CONFIG_DIRS);
2. A data file ($XDG_DATA_HOME:$XDG_DATA_DIRS); or
3. A non-essential (cache) file ($XDG_CACHE_HOME).

It is recommended that your application put its files in a subdirectory of the above directories. Usually, something like $XDG_DATA_DIRS/<application>/filename or $XDG_DATA_DIRS/<vendor>/<application>/filename.

When loading, you first try to load the file from the user-specific directories ($XDG_*_HOME) and, if failed, from system directories ($XDG_*_DIRS). When saving, save to user-specific directories only (since the user probably won't have write access to system directories).

For other, more user-oriented directories, refer to the XDG User Directories Specification. It defines directories for the Desktop, downloads, documents, videos, etc.

Solution 2:

1. Generally system/global config is stored somewhere under /etc.
2. User-specific config is stored in the user's home directory, often as a hidden file, sometimes as a hidden directory containing non-hidden files (and possibly more subdirectories).

Generally speaking, command line options will override environment variables which will override user defaults which will override system defaults.

Solution 3:

Newer Applications

Follow XDG Base Directory Specification usually ~/.config/yourapp/* can be INF, JSON, YML or whatever format floats your boat, and whatever files... yourapp should match your executable name, or be namespaced with your organization/company/username/handle to ~/.config/yourorg/yourapp/*

Older Applications

Per-user configuration, usually right in your home directory...

• ~/.yourapp file for a single file
• ~/.yourapp/ for multiple files + data usually in ~/.yourapp/config

Global configurations are generally in /etc/appname file or /etc/appname/ directory.

Global App data: /var/lib/yourapp/

Cache data: /var/cache/

Log data: /var/log/yourapp/

Some additional info from tutorialhelpdesk.com

The directory structure of Linux/other Unix-like systems and directory details.

In Windows, almost all programs install their files (all files) in the directory named: 'Program Files' Such is not the case in Linux. The directory system categorizes all installed files. All configuration files are in /etc, all binary files are in /bin or /usr/bin or /usr/local/bin. Here is the entire directory structure along with what they contain:

/ - Root directory that forms the base of the file system. All files and directories are logically contained inside the root directory regardless of their physical locations.

/bin - Contains the executable programs that are part of the Linux operating system. Many Linux commands, such as cat, cp, ls, more, and tar, are locate in /bin

/boot - Contains the Linux kernel and other files needed by LILO and GRUB boot managers.

/dev - Contains all device files. Linux treats each device as a special file. All such files are located in /dev.

/etc - Contains most system configuration files and the initialisation scripts in /etc/rc.d subdirectory.

/home - Home directory is the parent to the home directories of users.

/lib - Contains library files, including loadable driver modules needed to boot the system.

/lost+found - Directory for lost files. Every disk partition has a lost+found directory.

/media - Directory for mounting files systems on removable media like CD-ROM drives, floppy disks, and Zip drives.

/mnt - A directory for temporarily mounted filesystems.

/opt - Optional software packages copy/install files here.

/proc - A special directory in a virtual filesystem. It contains the information about various aspects of a Linux system.

/root - Home directory of the root user.

/sbin - Contains administrative binary files. Commands such as mount, shutdown, umount, reside here.

/srv - Contains data for services (HTTP, FTP, etc.) offered by the system.

/sys - A special directory that contains information about the devices, as seen by the Linux kernel.

/tmp - Temporary directory which can be used as a scratch directory (storage for temporary files). The contents of this directory are cleared each time the system boots.

/usr - Contains subdirectories for many programs such as the X Window System.

/usr/bin - Contains executable files for many Linux commands. It is not part of the core Linux operating system.

/usr/include - Contains header files for C and C++ programming languages

/usr/lib - Contains libraries for C and C++ programming languages.

/usr/local - Contains local files. It has a similar directories as /usr contains.

/usr/sbin - Contains administrative commands.

/usr/share - Contains files that are shared, like, default configuration files, images, documentation, etc.

/usr/src - Contains the source code for the Linux kernel.

/var - Contains various system files such as log, mail directories, print spool, etc. which tend to change in numbers and size over time.

/var/cache - Storage area for cached data for applications.

/var/lib - Contains information relating to the current state of applications. Programs modify this when they run.

/var/lock - Contains lock files which are checked by applications so that a resource can be used by one application only.

/var/log - Contains log files for different applications.

/var/mail - Contains users' emails.

/var/opt - Contains variable data for packages stored in /opt directory.

/var/run - Contains data describing the system since it was booted.

/var/spool - Contains data that is waiting for some kind of processing.

/var/tmp - Contains temporary files preserved between system reboots.