Add a --detach option

Allows kitty to detach itself from the controlling terminal. Useful
when launching kitty from a GUI environment with broken stdout/stderr or
when launching from a terminal that you want to close later without
affecting the launched kitty instance.

kitty/data-types.c

@@ -31,6 +31,17 @@ change_wcwidth_wrap(PyObject UNUSED *self, PyObject *use9) {
     Py_RETURN_NONE;
 }
 
+static PyObject*
+redirect_std_streams(PyObject UNUSED *self, PyObject *args) {
+    char *devnull = NULL;
+    if (!PyArg_ParseTuple(args, "s", &devnull)) return NULL;
+    if (freopen(devnull, "r", stdin) == NULL) return PyErr_SetFromErrno(PyExc_EnvironmentError);
+    if (freopen(devnull, "w", stdout) == NULL) return PyErr_SetFromErrno(PyExc_EnvironmentError);
+    if (freopen(devnull, "w", stderr) == NULL)  return PyErr_SetFromErrno(PyExc_EnvironmentError);
+    Py_RETURN_NONE;
+}
+
+
 static PyMethodDef module_methods[] = {
     GL_METHODS
     {"drain_read", (PyCFunction)drain_read, METH_O, ""},
@@ -38,6 +49,7 @@ static PyMethodDef module_methods[] = {
     {"parse_bytes_dump", (PyCFunction)parse_bytes_dump, METH_VARARGS, ""},
     {"read_bytes", (PyCFunction)read_bytes, METH_VARARGS, ""},
     {"read_bytes_dump", (PyCFunction)read_bytes_dump, METH_VARARGS, ""},
+    {"redirect_std_streams", (PyCFunction)redirect_std_streams, METH_VARARGS, ""},
     {"wcwidth", (PyCFunction)wcwidth_wrap, METH_O, ""},
     {"change_wcwidth", (PyCFunction)change_wcwidth_wrap, METH_O, ""},
 #ifndef __APPLE__

kitty/main.py

@@ -33,7 +33,7 @@ except ImportError:
     GLFW_X11_WM_CLASS_NAME = GLFW_X11_WM_CLASS_CLASS = None
 from .layout import all_layouts
 from .shaders import GL_VERSION
-from .utils import safe_print
+from .utils import safe_print, detach
 
 
 defconf = os.path.join(config_dir, 'kitty.conf')
@@ -99,6 +99,13 @@ def option_parser():
         default=False,
         help=_('Output commands received from child process to stdout')
     )
+    if not isosx:
+        a(
+            '--detach',
+            action='store_true',
+            default=False,
+            help=_('Detach from the controlling terminal, if any')
+        )
     a(
         '--replay-commands',
         default=None,
@@ -265,7 +272,11 @@ def main():
     if os.environ.pop('KITTY_LAUNCHED_BY_LAUNCH_SERVICES',
                       None) == '1' and getattr(sys, 'frozen', True):
         os.chdir(os.path.expanduser('~'))
+    if not os.path.isdir(os.getcwd()):
+        os.chdir(os.path.expanduser('~'))
     args = option_parser().parse_args()
+    if getattr(args, 'detach', False):
+        detach()
     if args.cmd:
         exec(args.cmd)
         return

kitty/utils.py

@@ -14,7 +14,7 @@ from functools import lru_cache
 from time import monotonic
 
 from .constants import isosx
-from .fast_data_types import glfw_get_physical_dpi, wcwidth as wcwidth_impl
+from .fast_data_types import glfw_get_physical_dpi, wcwidth as wcwidth_impl, redirect_std_streams
 from .rgb import Color, to_color
 
 
@@ -215,3 +215,14 @@ def open_url(url, program='default'):
         cmd = shlex.split(program)
     cmd.append(url)
     subprocess.Popen(cmd).wait()
+
+
+def detach(fork=True, setsid=True, redirect=True):
+    if fork:
+        # Detach from the controlling process.
+        if os.fork() != 0:
+            raise SystemExit(0)
+    if setsid:
+        os.setsid()
+    if redirect:
+        redirect_std_streams(os.devnull)