Do no confuse the question here with how to list processes graphically, that is not what I am asking.

In the Terminal, how can i see which processes have a GUI? as in things like firefox, vlc, geany, nautilus etc... all have a gui. I would like more information about which processes are using window manager resources, and I would like to do that from the terminal.

How do I get more information about THOSE types of process?

I've been trying to use the ps command, but I would entertain any terminal command to help me solve this.

UPDATE: I see something I like in pstree which is the tree from which all the graphical process I am interested are spawned from:

     │         ├─lightdm─┬─init─┬─
     │         │         │      ├─firefox───55*[{firefox}]
     │         │         │      ├─geany─┬─bash
     │         │         │      │       
     │         │         │      ├─gnome-terminal─┬─bash───pstree

  • Maybe with pstree
    – jcbermu
    Commented Mar 11, 2015 at 14:46
  • 1
    To clarify, what exactly do you mean by "have a GUI"? For instance, xterm or gnome-terminal are X clients that use X resources and are managed by your window manager, but it would be hard to argue that they actually have GUIs.
    – jamesqf
    Commented Mar 11, 2015 at 18:28
  • Imagine you press alt+tab. a small list of applications appears, they are all graphical applications, They are not things like panel applets. I am looking for a programmatic way to identify those applications, for use in shell scripts. There are other programs running, as processes, I am looking for a way to identify the window component of an application, with a shell script. At this point window ID seems like the best bet. Im not ruling as the best or only option, Im asking: "how do I get more information about the running programs with graphical user interfaces"
    – j0h
    Commented Mar 11, 2015 at 23:23
  • To be exact, some processes may have a GUI which it is shown on some oter X display, like another computer over the network. When a lightweight X terminal hardware is used, all programs have the GUI shown on another computer. (Looking for programms that have a GUI on the current X display would solve it, and do what you most probably mean. The X display needs to be known in the terminal ($DISPLAY, often :0.0) for this, which may be difficult in a cron job or so. ) Commented Mar 18, 2015 at 12:23

4 Answers 4


Try xrestop or xrestop -b.

It is intended to measure how many X resources each X window consumes, but as a small bonus identifies name of the windows and corresponding PIDs.

  • its so close to being cool. But it also gives me an idea, that the info I wnat might be part of X
    – j0h
    Commented Mar 11, 2015 at 15:18
  • 3
    @j0h Well... try to define what it means to "have a GUI". In the end it means that the process is sending some commands to the GUI server of the OS to display some windows. X is the display server for linux systems, hence all processes with a GUI somehow "use" X. There's really no real difference between GUI and non-GUI process from the point of view of the kernel, and as such there isn't a simple system call to determine whether a process has or not a GUI.
    – Bakuriu
    Commented Mar 11, 2015 at 16:58

xlsclients is close (and a standard part of X), it lists the X server's clients. But, there might not be a 1:1 mapping between what you consider an "application" and what X considers a "client". My single running instance of LyX consumes 13 clients for example, if I use xlsclients -l (long-form output) I can see only one of them has a defined "Icon Name", but this is only a hint. Also, since it uses XQueryTree() it may miss some windows (it doesn't find any xpdf windows I have open).

It also doesn't give very much information, what you can do though is use xlsclients -l to obtain the window id, and query each window with xprop -id $ID. For more details on a window, use xwinifo, though it cares about "windows" which are not the same thing as clients or applications:

xwininfo -root -children
xwininfo -root -tree  # indented view

Depending on your window manager, you may be able to inspect certain window properties (e.g. _NET_xxx or _NET_WM_xxxx properties) to determine if something is an "application". If the window manager client or GUI library sets it (any contemporary one should) the _NET_WM_PID property is the simplest (though imperfect) way to associate a PID with a specific window. I don't know of a tool that ties all these pieces together.

I use the window manager FVWM, I can talk directly to it using FvwmCommand, e.g. FvwmCommand -i1 send_windowlist shows me the list of windows. @Arkadiusz' suggestion to use wmctrl seems like a good and window manager agnostic way to do the same thing.

One more trick is to query the root window's _WIN_CLIENT_LIST, via bash:

$ xwininfo -root 
xwininfo: Window id: 0x69 (the root window) (has no name)

$ IFS=",= " read -a win < <(xprop -notype -id 0x69 32x  _WIN_CLIENT_LIST )

$ for ((ww=1; ww<${#win[*]}; ww++)); do 
    printf "%i %s\n" $ww ${win[$ww]};  
    xprop -id ${win[ww]} -notype _NET_WM_PID WM_NAME WM_CLASS \
                                 WM_ICON_NAME WM_CLIENT_LEADER; 

This exactly matches what my WM lists as windows (without those I have configured to be excluded from the WM window list). Child windows set WM_CLIENT_LEADER to their parent (for session management), though the parent window may not be visible (firefox does this), and may point to itself.

xrestop gets my vote though.


Alternatively, if you're using EWMH compatible window manager you can give wmctrl a try. It can list all windows being managed by the window manager + their PIDs:

$ wmctrl  -lp | awk  '{ print $3 }' | sort | uniq

Yeah, you need X for this. But I don't know of a tool that does this out-of-the-box.

An app with a GUI is a client on the local X server. But, a client on the local X server is not necessarily an app with a GUI. Also, a client on the local X server is not necessarily a local process, and a local process with a GUI may well be a client on a remote X server.

I think you'll get close with xlsclients or xlsclients -a. With the -l option it will also give you (among other things) the Window ID. But it can't give you the PID. X does not, in general, know it.

Pondering: With root access, you could grep through lsof output to see which (local!) processes access the (local!) X server(s). So perhaps there's some tool out there already doing this? I don't know.

  • This is probably completely unrelated, but how does Alt+Tab work?
    – j0h
    Commented Mar 11, 2015 at 16:41
  • @j0h To switch between windows? That would be handled by the window manager. Unless you're somehow working without a window manager, just let the window manager do this. If you want to perform Alt+Tab from a script, read up on how to control your window manager (I don't believe you've told us which you're using?) from a script. Commented Mar 11, 2015 at 17:57
  • lsof can list unix or abstract domain sockets, but can't tell what they connect to. Commented Mar 12, 2015 at 13:45
  • @StéphaneChazelas My bad. I thought it would be possible to match something like NODE or DEVICE (address) to see which two ends were connected. It isn't. Commented Mar 12, 2015 at 15:33
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    Using that perl script, on Linux, you could do sudo lsof -aUc Xorg | sudo that-script to list the local clients using the unix/abstract sockets. sudo lsof -ai tcp -c Xorg to list the clients using TCP sockets. Commented Mar 17, 2015 at 9:40

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