why does g_file_copy return Operation not supported when DBUS_SESSION_BUS_ADDRESS is not set

Question

The following code works fine as a normal user session:

#include <gio/gio.h>
int main()
{
        const gchar *uri = "https://stackoverflow.com/questions/5758770/";
        GFile *in;
        GFile *out;
        GError *error = NULL;
        gboolean ret;
        g_type_init();
        in = g_file_new_for_uri(uri);
        out = g_file_new_for_path("/tmp/a");
        ret = g_file_copy(in, out, G_FILE_COPY_OVERWRITE,
                          NULL, NULL, NULL, &error);
        if (!ret)
                g_message("%s", error->message);
        return 0;
}

(Taken from glib-network-connection-example)

But when 'su -' to another user and execute the same binary, I get the following error:

**** Message: Operation not supported**

strace dump below:

execve("./uri_copy", ["./uri_copy"], [/* 24 vars */]) = 0
brk(0)                                  = 0x2318000
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fc8757f3000
access("/etc/ld.so.preload", R_OK)      = -1 ENOENT (No such file or directory)
open("/etc/ld.so.cache", O_RDONLY|O_CLOEXEC) = 3
fstat(3, {st_mode=S_IFREG|0644, st_size=113424, ...}) = 0
mmap(NULL, 113424, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7fc8757d7000
close(3)                                = 0
open("/usr/lib/libgio-2.0.so.0", O_RDONLY|O_CLOEXEC) = 3
read(3, "\177ELF\2\1\1\0\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0\300\21\3\0\0\0\0\0"..., 832) = 832
fstat(3, {st_mode=S_IFREG|0755, st_size=7332859, ...}) = 0
mmap(NULL, 3481536, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7fc875281000
mprotect(0x7fc8753cd000, 2093056, PROT_NONE) = 0
mmap(0x7fc8755cc000, 24576, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x14b000) = 0x7fc8755cc000
mmap(0x7fc8755d2000, 4032, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x7fc8755d2000
close(3)                                = 0
open("/usr/lib/libgobject-2.0.so.0", O_RDONLY|O_CLOEXEC) = 3
read(3, "\177ELF\2\1\1\0\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0p\256\0\0\0\0\0\0"..., 832) = 832
fstat(3, {st_mode=S_IFREG|0755, st_size=1571328, ...}) = 0
mmap(NULL, 2416416, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7fc875033000
mprotect(0x7fc87507f000, 2097152, PROT_NONE) = 0
mmap(0x7fc87527f000, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x4c000) = 0x7fc87527f000
close(3)                                = 0
open("/usr/lib/libglib-2.0.so.0", O_RDONLY|O_CLOEXEC) = 3
read(3, "\177ELF\2\1\1\0\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0\220\230\1\0\0\0\0\0"..., 832) = 832
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fc8757d6000
fstat(3, {st_mode=S_IFREG|0755, st_size=4565491, ...}) = 0
mmap(NULL, 3279624, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7fc874d12000
mprotect(0x7fc874e31000, 2097152, PROT_NONE) = 0
mmap(0x7fc875031000, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x11f000) = 0x7fc875031000
close(3)                                = 0
open("/lib/libpthread.so.0", O_RDONLY|O_CLOEXEC) = 3
read(3, "\177ELF\2\1\1\0\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0\340l\0\0\0\0\0\0"..., 832) = 832
fstat(3, {st_mode=S_IFREG|0755, st_size=776444, ...}) = 0
mmap(NULL, 2212768, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7fc874af5000
mprotect(0x7fc874b0c000, 2097152, PROT_NONE) = 0
mmap(0x7fc874d0c000, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x17000) = 0x7fc874d0c000
mmap(0x7fc874d0e000, 13216, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x7fc874d0e000
close(3)                                = 0
open("/lib/libc.so.6", O_RDONLY|O_CLOEXEC) = 3
read(3, "\177ELF\2\1\1\3\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0 \30\2\0\0\0\0\0"..., 832) = 832
fstat(3, {st_mode=S_IFREG|0755, st_size=10464009, ...}) = 0
mmap(NULL, 3820672, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7fc874750000
mprotect(0x7fc8748eb000, 2097152, PROT_NONE) = 0
mmap(0x7fc874aeb000, 24576, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x19b000) = 0x7fc874aeb000
mmap(0x7fc874af1000, 15488, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x7fc874af1000
close(3)                                = 0
open("/usr/lib/libgthread-2.0.so.0", O_RDONLY|O_CLOEXEC) = 3
read(3, "\177ELF\2\1\1\0\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0000\6\0\0\0\0\0\0"..., 832) = 832
fstat(3, {st_mode=S_IFREG|0755, st_size=10190, ...}) = 0
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fc8757d5000
mmap(NULL, 2100144, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7fc87454f000
mprotect(0x7fc874550000, 2093056, PROT_NONE) = 0
mmap(0x7fc87474f000, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0) = 0x7fc87474f000
close(3)                                = 0
open("/usr/lib/libffi.so.6", O_RDONLY|O_CLOEXEC) = 3
read(3, "\177ELF\2\1\1\0\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0@\30\0\0\0\0\0\0"..., 832) = 832
fstat(3, {st_mode=S_IFREG|0755, st_size=160444, ...}) = 0
mmap(NULL, 2128152, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7fc874347000
mprotect(0x7fc87434e000, 2097152, PROT_NONE) = 0
mmap(0x7fc87454e000, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x7000) = 0x7fc87454e000
close(3)                                = 0
open("/usr/lib/libgmodule-2.0.so.0", O_RDONLY|O_CLOEXEC) = 3
read(3, "\177ELF\2\1\1\0\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0\240\21\0\0\0\0\0\0"..., 832) = 832
fstat(3, {st_mode=S_IFREG|0755, st_size=48372, ...}) = 0
mmap(NULL, 2107576, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7fc874144000
mprotect(0x7fc874147000, 2093056, PROT_NONE) = 0
mmap(0x7fc874346000, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x2000) = 0x7fc874346000
close(3)                                = 0
open("/lib/libdl.so.2", O_RDONLY|O_CLOEXEC) = 3
read(3, "\177ELF\2\1\1\0\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0\260\16\0\0\0\0\0\0"..., 832) = 832
fstat(3, {st_mode=S_IFREG|0755, st_size=110348, ...}) = 0
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fc8757d4000
mmap(NULL, 2109720, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7fc873f40000
mprotect(0x7fc873f42000, 2097152, PROT_NONE) = 0
mmap(0x7fc874142000, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x2000) = 0x7fc874142000
close(3)                                = 0
open("/lib/librt.so.1", O_RDONLY|O_CLOEXEC) = 3
read(3, "\177ELF\2\1\1\0\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0\300\"\0\0\0\0\0\0"..., 832) = 832
fstat(3, {st_mode=S_IFREG|0755, st_size=197331, ...}) = 0
mmap(NULL, 2128888, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7fc873d38000
mprotect(0x7fc873d3f000, 2093056, PROT_NONE) = 0
mmap(0x7fc873f3e000, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x6000) = 0x7fc873f3e000
close(3)                                = 0
open("/lib/libz.so.1", O_RDONLY|O_CLOEXEC) = 3
read(3, "\177ELF\2\1\1\0\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0\360 \0\0\0\0\0\0"..., 832) = 832
fstat(3, {st_mode=S_IFREG|0755, st_size=102874, ...}) = 0
mmap(NULL, 2188616, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7fc873b21000
mprotect(0x7fc873b37000, 2097152, PROT_NONE) = 0
mmap(0x7fc873d37000, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x16000) = 0x7fc873d37000
close(3)                                = 0
open("/lib/libresolv.so.2", O_RDONLY|O_CLOEXEC) = 3
read(3, "\177ELF\2\1\1\0\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0\260:\0\0\0\0\0\0"..., 832) = 832
fstat(3, {st_mode=S_IFREG|0755, st_size=397849, ...}) = 0
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fc8757d3000
mmap(NULL, 2189936, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7fc87390a000
mprotect(0x7fc87391e000, 2093056, PROT_NONE) = 0
mmap(0x7fc873b1d000, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x13000) = 0x7fc873b1d000
mmap(0x7fc873b1f000, 6768, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x7fc873b1f000
close(3)                                = 0
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fc873909000
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fc873908000
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fc873907000
arch_prctl(ARCH_SET_FS, 0x7fc873908700) = 0
mprotect(0x7fc874aeb000, 16384, PROT_READ) = 0
mprotect(0x7fc873b1d000, 4096, PROT_READ) = 0
mprotect(0x7fc874d0c000, 4096, PROT_READ) = 0
mprotect(0x7fc873f3e000, 4096, PROT_READ) = 0
mprotect(0x7fc874142000, 4096, PROT_READ) = 0
mprotect(0x7fc8757f4000, 4096, PROT_READ) = 0
munmap(0x7fc8757d7000, 113424)          = 0
set_tid_address(0x7fc8739089d0)         = 3023
set_robust_list(0x7fc8739089e0, 24)     = 0
futex(0x7fff6deb5014, FUTEX_WAIT_BITSET_PRIVATE|FUTEX_CLOCK_REALTIME, 1, NULL, 7fc873908700) = -1 EAGAIN (Resource temporarily unavailable)
rt_sigaction(SIGRTMIN, {0x7fc874afb7d0, [], SA_RESTORER|SA_SIGINFO, 0x7fc874b047b0}, NULL, 8) = 0
rt_sigaction(SIGRT_1, {0x7fc874afb850, [], SA_RESTORER|SA_RESTART|SA_SIGINFO, 0x7fc874b047b0}, NULL, 8) = 0
rt_sigprocmask(SIG_UNBLOCK, [RTMIN RT_1], NULL, 8) = 0
getrlimit(RLIMIT_STACK, {rlim_cur=8192*1024, rlim_max=RLIM64_INFINITY}) = 0
brk(0)                                  = 0x2318000
brk(0x2339000)                          = 0x2339000
getresuid([0], [0], [0])                = 0
getresgid([0], [0], [0])                = 0
openat(AT_FDCWD, "/usr/lib/gio/modules", O_RDONLY|O_NONBLOCK|O_DIRECTORY|O_CLOEXEC) = 3
stat("/usr/lib/gio/modules/giomodule.cache", {st_mode=S_IFREG|0644, st_size=317, ...}) = 0
open("/usr/lib/charset.alias", O_RDONLY) = -1 ENOENT (No such file or directory)
open("/usr/lib/gio/modules/giomodule.cache", O_RDONLY) = 4
fstat(4, {st_mode=S_IFREG|0644, st_size=317, ...}) = 0
read(4, "libgvfsdbus.so: gio-vfs,gio-volu"..., 317) = 317
close(4)                                = 0
getdents(3, /* 17 entries */, 32768)    = 704
stat("/usr/lib/gio/modules/libgvfsdbus.so", {st_mode=S_IFREG|0755, st_size=1008539, ...}) = 0
stat("/usr/lib/gio/modules/libgiognutls.so", {st_mode=S_IFREG|0755, st_size=528214, ...}) = 0
stat("/usr/lib/gio/modules/libgiolibproxy.so", {st_mode=S_IFREG|0755, st_size=38152, ...}) = 0
stat("/usr/lib/gio/modules/libgiognomeproxy.so", {st_mode=S_IFREG|0755, st_size=61385, ...}) = 0
stat("/usr/lib/gio/modules/libgsettingsgconfbackend.so", {st_mode=S_IFREG|0755, st_size=80091, ...}) = 0
stat("/usr/lib/gio/modules/libgioremote-volume-monitor.so", {st_mode=S_IFREG|0755, st_size=520847, ...}) = 0
stat("/usr/lib/gio/modules/libdconfsettings.so", {st_mode=S_IFREG|0755, st_size=197917, ...}) = 0
getdents(3, /* 0 entries */, 32768)     = 0
close(3)                                = 0
stat("/usr/lib/gio/modules/libgvfsdbus.so", {st_mode=S_IFREG|0755, st_size=1008539, ...}) = 0
futex(0x7fc8741430c8, FUTEX_WAKE_PRIVATE, 2147483647) = 0
open("/usr/lib/gio/modules/libgvfsdbus.so", O_RDONLY|O_CLOEXEC) = 3
read(3, "\177ELF\2\1\1\0\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0`\311\0\0\0\0\0\0"..., 832) = 832
fstat(3, {st_mode=S_IFREG|0755, st_size=1008539, ...}) = 0
mmap(NULL, 2296960, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7fc8736d6000
mprotect(0x7fc873705000, 2097152, PROT_NONE) = 0
mmap(0x7fc873905000, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x2f000) = 0x7fc873905000
close(3)                                = 0
open("/etc/ld.so.cache", O_RDONLY|O_CLOEXEC) = 3
fstat(3, {st_mode=S_IFREG|0644, st_size=113424, ...}) = 0
mmap(NULL, 113424, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7fc8736ba000
close(3)                                = 0
open("/usr/lib/libgvfscommon.so.0", O_RDONLY|O_CLOEXEC) = 3
read(3, "\177ELF\2\1\1\0\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0 .\1\0\0\0\0\0"..., 832) = 832
fstat(3, {st_mode=S_IFREG|0755, st_size=935965, ...}) = 0
mmap(NULL, 2338440, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7fc87347f000
mprotect(0x7fc8734b5000, 2093056, PROT_NONE) = 0
mmap(0x7fc8736b4000, 24576, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x35000) = 0x7fc8736b4000
close(3)                                = 0
open("/lib/libpcre.so.1", O_RDONLY|O_CLOEXEC) = 3
read(3, "\177ELF\2\1\1\0\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0\300\23\0\0\0\0\0\0"..., 832) = 832
fstat(3, {st_mode=S_IFREG|0755, st_size=270107, ...}) = 0
mmap(NULL, 2356392, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7fc87323f000
mprotect(0x7fc87327e000, 2097152, PROT_NONE) = 0
mmap(0x7fc87347e000, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x3f000) = 0x7fc87347e000
close(3)                                = 0
open("/lib/libudev.so.1", O_RDONLY|O_CLOEXEC) = 3
read(3, "\177ELF\2\1\1\0\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0@L\0\0\0\0\0\0"..., 832) = 832
fstat(3, {st_mode=S_IFREG|0755, st_size=1088628, ...}) = 0
mmap(NULL, 2173032, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7fc87302c000
mprotect(0x7fc87303d000, 2097152, PROT_NONE) = 0
mmap(0x7fc87323d000, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x11000) = 0x7fc87323d000
close(3)                                = 0
open("/lib/libutil.so.1", O_RDONLY|O_CLOEXEC) = 3
read(3, "\177ELF\2\1\1\0\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0\360\16\0\0\0\0\0\0"..., 832) = 832
fstat(3, {st_mode=S_IFREG|0755, st_size=33117, ...}) = 0
mmap(NULL, 2105600, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7fc872e29000
mprotect(0x7fc872e2b000, 2093056, PROT_NONE) = 0
mmap(0x7fc87302a000, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x1000) = 0x7fc87302a000
close(3)                                = 0
mprotect(0x7fc87302a000, 4096, PROT_READ) = 0
mprotect(0x7fc87323d000, 4096, PROT_READ) = 0
munmap(0x7fc8736ba000, 113424)          = 0
munmap(0x7fc8736d6000, 2296960)         = 0
munmap(0x7fc87347f000, 2338440)         = 0
munmap(0x7fc87323f000, 2356392)         = 0
munmap(0x7fc87302c000, 2173032)         = 0
munmap(0x7fc872e29000, 2105600)         = 0
open("/usr/lib64/gconv/gconv-modules.cache", O_RDONLY) = -1 ENOENT (No such file or directory)
open("/usr/lib64/gconv/gconv-modules", O_RDONLY|O_CLOEXEC) = 3
fstat(3, {st_mode=S_IFREG|0644, st_size=56302, ...}) = 0
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fc8757f2000
read(3, "# GNU libc iconv configuration.\n"..., 4096) = 4096
read(3, "lias\tCSISO141JUSIB1002//\tJUS_I.B"..., 4096) = 4096
read(3, "odule\t\tcost\nalias\tISO-IR-110//\t\t"..., 4096) = 4096
read(3, "9-14//\nalias\tL8//\t\t\tISO-8859-14/"..., 4096) = 4096
read(3, "CSEBCDICES//\t\tEBCDIC-ES//\nalias\t"..., 4096) = 4096
read(3, "IBM284//\nalias\tEBCDIC-CP-ES//\t\tI"..., 4096) = 4096
brk(0x235a000)                          = 0x235a000
read(3, "ias\t864//\t\t\tIBM864//\nalias\tCSIBM"..., 4096) = 4096
read(3, "lias\tCSIBM939//\t\tIBM939//\nmodule"..., 4096) = 4096
read(3, "alias\tcsGB2312//\t\tEUC-CN//\nalias"..., 4096) = 4096
read(3, "//\t\tISO-2022-CN-EXT//\nmodule\tISO"..., 4096) = 4096
read(3, "st\nalias\tISO-IR-55//\t\tISO_5428//"..., 4096) = 4096
read(3, "\tARMSCII-8//\t\tARMSCII-8\t1\n\n#\tfro"..., 4096) = 4096
read(3, "2//\t\tIBM1112\t\t1\n\n#\tfrom\t\t\tto\t\t\tm"..., 4096) = 4096
read(3, "module\tIBM9448//\t\tINTERNAL\t\tIBM9"..., 4096) = 3054
read(3, "", 4096)                       = 0
close(3)                                = 0
munmap(0x7fc8757f2000, 4096)            = 0
futex(0x7fc874af08f8, FUTEX_WAKE_PRIVATE, 2147483647) = 0
write(2, "** Message: Operation not suppor"..., 36** Message: Operation not supported
) = 36
exit_group(0)                           = ?
+++ exited with 0 +++

I've narrowed down the issue to the DBUS_SESSION_BUS_ADDRESS variable not being set.

I would like to know why the above solution requires dbus as there is no mention of this in the glib/gio documentation and is there a download file solution that does not require dbus, or alternatively, can I set DBUS_SESSION_BUS_ADDRESS to something that would make it work regardless of how I switch to another user's session.

Try to `strace` your program. You'll find out which syscalls failed. — Basile Starynkevitch, Feb 03 '13 at 08:37
I've added the strace output whilst running the binary as root. It start to deviate from the line 'mprotect(0x7fc87302a000, 4096, PROT_READ) = 0', and I still cannot determine what could be causing it. — Wayne, Feb 04 '13 at 07:45
I've discovered that this problem occurs when I 'su -' as any other user and not just root. If I log in as another user via GDM, then the problem does not occur. It is only when I su into another user that this problem occurs. I think it is something to do with dbus sessions (I can see extra dbus activity in the strace during a successful execution), but I don't see why dbus should be involved in such an operation. — Wayne, Feb 04 '13 at 08:17
At a guess, the http handling is done via a fuse module, and when you change user the proper fuse backend doesn't get started for some reason- but it does get started when you run a desktop session as that user (i.e. logs in via gdm) — nos, Feb 04 '13 at 09:15

score 4 · Accepted Answer · edited May 23 '17 at 12:34

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Local file access through GIO does not require DBus, but network file access is carried out via the gvfsd, and DBus is used to communicate between your program and the daemon. More technical details can be found in the GNOME 2.22 Release Notes.

The answer given in this question Access another user's D-Bus session should fix your problem.

edited May 23 '17 at 12:34

Community

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answered Mar 18 '13 at 16:26

iain

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why does g_file_copy return Operation not supported when DBUS_SESSION_BUS_ADDRESS is not set

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