Linux has no internet

Work down this list. Each step rules out one layer, and the first one that fails is the answer.

1. Is the network gate open?#

The Sandbox tab's Network gate detaches the virtual network card. It is kept across restarts, so an instance you sealed last week is still sealed.

This is by far the most common cause, and it looks exactly like a broken connection: no internet, no local network, SSH not answering. Note that msl shells, the Terminal tab and MSL Files keep working with it closed, because they do not use the network — so "the terminal works but nothing downloads" points straight here.

2. Does the guest have an address?#

In the instance:

ip addr
ip route

You want an address on the main interface and a default route. If there is no address, ask for one:

sudo dhclient -v

3. Can it reach anything by number?#

ping -c 3 1.1.1.1

Working here but not by name means DNS, which is the next step. Failing here with the gate open points at your Mac's own connection — check that the Mac itself is online.

4. Can it resolve names?#

getent hosts deb.debian.org
cat /etc/resolv.conf

"Temporary failure in name resolution" from apt is almost always this. /etc/resolv.conf should name a resolver; if it is empty or points somewhere unreachable, that is the fault.

5. Is the clock right?#

A clock that is badly wrong breaks anything using certificates, which looks like a network problem: downloads fail, apt complains that release files are not valid yet. See The clock is wrong.

What each symptom usually means#