ui: ignore EIO in write_err Hgs signal handler will catch the signal for example if the terminal hg is running in is closed. That will make it try to warn that it was 'killed', but that might fail with EIO and cause hg to exit with an unhandled exception. Normally nobody cares, but system error handlers such as Fedoras abrt will notice and report https://bugzilla.redhat.com/show_bug.cgi?id=596594 .