Prior to 3.2, /proc/sys/kernel/hostname isn't a pollable file and
sd_event_add_io will return EPERM. Ignore this failure, since it isn't
critical to journald operation.
Reported and tested by user sraue on IRC.
r = sd_event_add_io(s->event, &s->hostname_event_source, s->hostname_fd, 0, dispatch_hostname_change, s);
if (r < 0) {
+ /* kernels prior to 3.2 don't support polling this file. Ignore
+ * the failure. */
+ if (r == -EPERM) {
+ log_warning("Failed to register hostname fd in event loop: %s. Ignoring.",
+ strerror(-r));
+ close_nointr_nofail(s->hostname_fd);
+ s->hostname_fd = -1;
+ return 0;
+ }
+
log_error("Failed to register hostname fd in event loop: %s", strerror(-r));
return r;
}