"No protocol specified" when starting X programs from a script

[Tino Keitel]

Hi,

I try to start an X application from a script, which is not called from
X. This works with the Xfce desktop, but does not with Gnome3.

The script sets DISPLAY=:0 and HOME to the user that owns the X
session. The application is started with user and group permissions for
the user that owns the X session.

Here is the strace output that causes the error:

socket(PF_FILE, SOCK_STREAM|SOCK_CLOEXEC, 0) = 3
connect(3, {sa_family=AF_FILE, path=@"/tmp/.X11-unix/X0"}, 20) = 0
getpeername(3, {sa_family=AF_FILE, path=@"/tmp/.X11-unix/X0"}, [20]) =
0
uname({sys="Linux", node="mac", ...})   = 0
access("/home/scorpion/.Xauthority", R_OK) = 0
open("/home/scorpion/.Xauthority", O_RDONLY) = 4
fstat(4, {st_mode=S_IFREG|0600, st_size=147, ...}) = 0
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1,
0) = 0x7f14373eb000
read(4, "\1\0\0\3mac\0\00212\0\22MIT-MAGIC-COOKIE-1\0"..., 4096) = 147
read(4, "", 4096)                       = 0
close(4)                                = 0
munmap(0x7f14373eb000, 4096)            = 0
fcntl(3, F_GETFL)                       = 0x2 (flags O_RDWR)
fcntl(3, F_SETFL, O_RDWR|O_NONBLOCK)    = 0
fcntl(3, F_SETFD, FD_CLOEXEC)           = 0
poll([{fd=3, events=POLLIN|POLLOUT}], 1, -1) = 1 ([{fd=3,
revents=POLLOUT}])
writev(3, [{"l\0\v\0\0\0\0\0\0\0\0\0", 12}, {"", 0}], 2) = 12
read(3, "\0\26\v\0\0\0\6\0", 8)         = 8
read(3, "No protocol specified\n\0\0", 24) = 24
write(2, "No protocol specified\n", 22No protocol specified
) = 22
close(3)                                = 0

Any hints what I'm doing wrong?

Regards,
Tino