- A very strange bug has just been found in macOS
- If a Mac is left on for (just over) 49 days, its networking functionality will fail completely
- Apparently the only cure is to reboot, but presumably Apple will now be working on an official fix.
Have you ever wondered what would happen if you left your Mac on for a couple of months at a time? Probably not, but you might be interested to know that if you did, the networking part of the operating system would crash.
Tom’s Hardware reports that Photon wrote a blog post about how it “found a time bomb in macOS’s TCP network,” an explosive element in the code that “detonates after exactly 49 days.”
Well, 49 days, 17 hours, two minutes and 47 seconds to be precise. When macOS has been running continuously for that exact period of time, the operating system will experience an “integer overflow” that “freezes the internal TCP timestamp clock.”
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When that happens, existing TCP network connections don’t expire as they should, they remain frozen in place, and eventually, as Photon explains: “The ephemeral ports are slowly exhausted and eventually no new TCP connections can be established. ICMP (ping) keeps working. Everything else dies.”
In short, networking on Mac becomes completely useless and the only solution is to restart the machine. Yes, the old “turn it off and on again” solution.
Photon, a company that facilitates the creation of artificial intelligence agents, found this bug on the Macs it uses to monitor Apple’s messaging service, and the company successfully reproduced the problem on two systems.
Obviously, this is not a problem that most of you (assuming you have a Mac) have to worry about. No everyday user leaves their machine on for 50 days straight; but in case you are ever inclined to do so, at least you are now warned. This is, of course, more of a technical issue that will affect the servers (running continuously for long periods) and that companies like Photon need to take into account.
The main cause of the problem is, as mentioned, integer overflow. This is where macOS assumes that a counter will only increase in numerical value, when in reality, it returns to zero after 50 days of running, and this is something that has also surprised Microsoft in the past. Photon reminds us that Windows 95 suffered a similar 49.7-day bug in which the kernel’s 32-bit millisecond counter overflowed, which in this case caused the PC to freeze completely.
Photon is apparently working on a fix to avoid having to reboot to repair the Mac, but presumably now that this bug has caught Apple’s attention we should see an official fix before long.
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