When the Internet is offline, what could be causing a Mac to grind to a halt?

[seggy]

I'm trying to work on an iMac Pro running Catalina today. My Internet is b0rked on my main wired link, so I'm reduced to tethering my phone.

One major problem however - when I'm connected to the wired LAN without Internet, the Mac slows to a crawl. It takes about 5 minutes for everything to launch, and continues being incredibly slow to do anything.

When I unplug the LAN cable and am solely on the tethered connection, everything is fine - or as fine as it gets in my current situation.

Any idea why? I just want to know why a non-functioning Internet would cause a Mac to drastically slow down.

I don't have a ton that auto-runs - Cryptomator, Outlook, Calendar, Mail, OneDrive, Magnet, Display Maid, iStat Menus. I also have about a dozen network shares off a NAS that come up on boot.

 

[chscag]

Great question. Same thing has happened to me with my iMac when our internet connection goes down. As soon as I shut off the lan connection, my tethered iPhone connection works normal and the machine resumes its normal speed.

It really screwed up my mind the first time it happened.

 

[jonwatso]

I've had the exact same issue and it ended being one drive.

 

[ssls6]

Make sure your tethered connection has higher priority (top of list) than the ethernet setting in System Prefs/Network.

 

[chrfr]

One major problem however - when I'm connected to the wired LAN without Internet, the Mac slows to a crawl. It takes about 5 minutes for everything to launch, and continues being incredibly slow to do anything.

Catalina checks apps for "notarization" status when they're launched. If there's no internet connection, this doesn't happen, and if there's a properly functioning connection, the process is quick, but if the connection exists but won't contact Apple, there will be a delay in launching.

 

[seggy]

Catalina checks apps for "notarization" status when they're launched. If there's no internet connection, this doesn't happen, and if there's a properly functioning connection, the process is quick, but if the connection exists but won't contact Apple, there will be a delay in launching.

What kind of delay are we talking about in that case?

It was at the point where clicking on an open app to close it takes like 30 seconds.

 

[FNH15]

It’s Mail - if you check Activity Monitor, you’ll see accountd taking up a significant amount of processor resources.

 

[seggy]

I'll check it when I try something similar next time.

Hopefully there isn't a next time - I signed up for leased Ethernet with a DSL & 4G backup back in March and it's now finally scheduled for installation.

 

[TripleB]

In our company we have similar problems as since Catalina. I am IT admin in my company and have been looking for a solution for a long time and I am almost desperate.

Our users can connect to the network, but only have access to the internet after they have authenticated themselves at the firewall. If you don't do that, the Macs become almost uselessly slow. It can take up to 5 minutes to start a program.

The same problem occurs when colleagues connect to public WLANs where you have to authenticate first.
Privately I have the same problem. A MacMini is connected to several audio interfaces in a LAN network without internet access to control the interfaces. The Mac gets so slow that it sometimes takes up to 5 minutes until the "Save As" dialog appears in my DAW.

Apple should consider that the Macs can also be in a network without internet access.

Is there any way to tell the Mac that it has no internet connection?

 

[mj_]

Make sure it doesn't have a default gateway configured.