Integrating systemctl --user and your Graphical Session

The problems with this are the same as with the dbus-update-activation-environment tool, which this just a reinvention of by the way.

There are a whole bunch of environment variables appropriate to a login session that are not appropriate to daemon processes that are running outwith a login session. From the headlined article one can pick quite a number of variables that are at best pointless in, and often outright misleading to and wrong for, daemon programs:

    GIO_LAUNCHED_DESKTOP_FILE_PID=3930
    GNOME_DESKTOP_SESSION_ID=this-is-deprecated
    LESSCLOSE=/usr/bin/lesspipe %s %s
    LESSOPEN=| /usr/bin/lesspipe %s
    LS_COLORS=rs=0:di=01;34:ln=01;36:mh=00:pi=40;33:so=01;35:do=01;35:bd=40;33;01:cd=40;33;01:or=40;31;01:mi=00:su=37;41:sg=30;43:ca=30;41:tw=30;42:ow=34;42:st=37;44:ex=01;32:*.tar=01;31:*.tgz=01;31:*.arc=01;31:*.arj=01;31:*.taz=01;31:*.lha=01;31:*.lz4=01;31:*.lzh=01;31:*.lzma=01;31:*.tlz=01;31:*.txz=01;31:*.tzo=01;31:*.t7z=01;31:*.zip=01;31:*.z=01;31:*.Z=01;31:*.dz=01;31:*.gz=01;31:*.lrz=01;31:*.lz=01;31:*.lzo=01;31:*.xz=01;31:*.bz2=01;31:*.bz=01;31:*.tbz=01;31:*.tbz2=01;31:*.tz=01;31:*.deb=01;31:*.rpm=01;31:*.jar=01;31:*.war=01;31:*.ear=01;31:*.sar=01;31:*.rar=01;31:*.alz=01;31:*.ace=01;31:*.zoo=01;31:*.cpio=01;31:*.7z=01;31:*.rz=01;31:*.cab=01;31:*.jpg=01;35:*.jpeg=01;35:*.gif=01;35:*.bmp=01;35:*.pbm=01;35:*.pgm=01;35:*.ppm=01;35:*.tga=01;35:*.xbm=01;35:*.xpm=01;35:*.tif=01;35:*.tiff=01;35:*.png=01;35:*.svg=01;35:*.svgz=01;35:*.mng=01;35:*.pcx=01;35:*.mov=01;35:*.mpg=01;35:*.mpeg=01;35:*.m2v=01;35:*.mkv=01;35:*.webm=01;35:*.ogm=01;35:*.mp4=01;35:*.m4v=01;35:*.mp4v=01;35:*.vob=01;35:*.qt=01;35:*.nuv=01;35:*.wmv=01;35:*.asf=01;35:*.rm=01;35:*.rmvb=01;35:*.flc=01;35:*.avi=01;35:*.fli=01;35:*.flv=01;35:*.gl=01;35:*.dl=01;35:*.xcf=01;35:*.xwd=01;35:*.yuv=01;35:*.cgm=01;35:*.emf=01;35:*.ogv=01;35:*.ogx=01;35:*.aac=00;36:*.au=00;36:*.flac=00;36:*.m4a=00;36:*.mid=00;36:*.midi=00;36:*.mka=00;36:*.mp3=00;36:*.mpc=00;36:*.ogg=00;36:*.ra=00;36:*.wav=00;36:*.oga=00;36:*.opus=00;36:*.spx=00;36:*.xspf=00;36:
    POWERLINE_COMMAND=powerline
    PROMPT_COMMAND=__bp_precmd_invoke_cmd; dbus-send --type=method_call --session --dest=org.pantheon.terminal /org/pantheon/terminal org.pantheon.terminal.ProcessFinished string:$PANTHEON_TERMINAL_ID string:"$(history 1 | cut -c 8-)" >/dev/null 2>&1;  __bp_interactive_mode;
    PWD=/home/naftuli
    SHLVL=2
    SSH_AGENT_PID=2095
    TERM=screen-256color
    VTE_VERSION=4205
    XDG_SEAT=seat0
    XDG_SEAT_PATH=/org/freedesktop/DisplayManager/Seat0
    XDG_SESSION_ID=c2
    XDG_SESSION_PATH=/org/freedesktop/DisplayManager/Session0
    XDG_VTNR=7

There are good reasons that daemons are run with known environments; and there are about four decades of system administrator horror stories of running daemons with things like the old "service" command and getting environment variables from a login session inherited into the service processes, to learn better from. Pushing the entire environment from an arbitrarily selected login session into the environments of services is a bad idea. At best, one should push only a carefully selected set of variables.

On Debian with the "new" per-user service management, the Desktop Bus people use dbus-update-activation-environment to push just three environment variables: DBUS_SESSION_BUS_ADDRESS, DISPLAY, and XAUTHORITY.

Of course, the elephant in the room is server daemons that are written to talk to arbitrary X displays that erroneously demand that they run with a DISPLAY variable already in the environment of the server daemon when it starts. A well-designed daemon arranges to have the DISPLAY information passed in to it. (In Unicode rxvt in its client-server mode, for example, the urxvtc program passes its DISPLAY environment variable in the message that it sends to the urxvtd server.)