cli: check for closed stdout/stderr

dvc/cli/__init__.py

@@ -1,6 +1,7 @@
 """This module provides an entrypoint to the dvc cli and parsing utils."""
 
 import logging
+import sys
 
 # Workaround for CPython bug. See [1] and [2] for more info.
 # [1] https://github.com/aws/aws-cli/blob/1.16.277/awscli/clidriver.py#L55
@@ -48,6 +49,16 @@ def main(argv=None):  # noqa: C901
     from dvc.exceptions import DvcException, NotDvcRepoError
     from dvc.logger import FOOTER, disable_other_loggers
 
+    # NOTE: stderr/stdout may be closed if we are running from dvc.daemon.
+    # On Linux we directly call cli.main after double forking and closing
+    # the copied parent's standard file descriptors. If we make any logging
+    # calls in this state it will cause an exception due to writing to a closed
+    # file descriptor.
+    if sys.stderr.closed:  # pylint: disable=using-constant-test
+        logging.disable()
+    elif sys.stdout.closed:  # pylint: disable=using-constant-test
+        logging.disable(logging.INFO)
+
     args = None
     disable_other_loggers()
 
@@ -68,7 +79,7 @@ def main(argv=None):  # noqa: C901
 
         logger.trace(args)
 
-        if not args.quiet:
+        if not sys.stdout.closed and not args.quiet:
             from dvc.ui import ui
 
             ui.enable()