xdg.theory.txt

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                                  ┃   XDG   ┃
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XDG_*                             #Environment variables meant for X11 (i.e. Linux|BSD|Android)
                                  #For user-wise directory location
                                  #Specification from FreeDesktop
                                  #For most of those directories, should namespace with application-named directory.

XDG_CONFIG_HOME                   #Main user configuration. Def: ~/.config/
                                  #Owned by user.
XDG_CONFIG_DIRS                   #Secondary user configuration.
                                  #:-delimited list of directories, from most priority to least
                                  #Def: /etc/xdg
                                  #On my machine, it is /etc/xdg/xdg-ubuntu:/etc/xdg
                                  #Owned by root.

XDG_DATA_HOME                     #Main user data. Def: ~/.local/share/
                                  #Owned by user.
XDG_DATA_DIRS                     #Secondary user data.
                                  #:-delimited list of directories, from most priority to least
                                  #Def: /usr/local/share/:/usr/share/
                                  #On my machine, it is /usr/share/ubuntu:/usr/local/share/:/usr/share/:/var/lib/snapd/desktop
                                  #Owned by root.

XDG_STATE_HOME                    #Data that is stateful between app restarts, but not:
                                  #  - user-facing (unlike XDG_DATA_HOME)
                                  #  - caching related (unlike XDG_CACHE_HOME)
                                  #Example: history, last state
                                  #Def: ~/.local/state/
                                  #Owned by user.

XDG_CACHE_HOME                    #Cache directory. Def: ~/.cache/
                                  #Owned by user.

XDG_RUNTIME_DIR                   #Session-wide user data. Removed on user logout.
                                  #On my machine, it is /run/user/USER_ID
                                  #Owned by user. Must be u+rxw,oa-rwx (0700)

BINARIES ==>                      #User-specific binaries. At ~/.local/bin/