Use qemu's virtconsole for the serial console #2834
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All the latest releases of distributions now have a systemd stub that knows how to read extra kernel command line arguments from SMBIOS (It was backported to CentOS Stream 9), so let's drop the default kernel command line and rely completely on passing the console to use via SMBIOS. This makes sure that users trying to deploy our images on bare metal have a working console. Users that want to access the system via the serial console will have to add the required console= argument themselves.
It cannot be installed on powerpc or s390x.
edk2 now has a virtio serial driver so let's switch to virtconsole for the serial console as it's significantly faster compared to the old ISA serial console.
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I confirm it works: |
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And it's fast: |
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While this does indeed work, for images targeting |
You can configure autologin with systemd credentials these days on a per tty basis. I would always do that instead of the autologin setting. I'll probably remove it at some point. |
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marc-hb
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Until mkosi v24 commit c236c9f7b9c82d3, `mkosi --autologin` used to be applied to four devices: console, tty1, ttyS0 and one architecture-dependent device. mkosi has some QEMU features of its own to boot the image. run_qemu.sh never used any of that. We should probably try (some of) it in the future but I digress. In that mkosi commit, `mkosi/qemu.py` (which we don't use) stopped using `ttyS0` and replaced it with the faster `/dev/hvc0` instead. The image building code (which we DO use!) was updated correspondingly without caring about backwards compatibility and dropped ttyS0 on the floor. Someone noted this in systemd/mkosi#2834 and the recommendation was to switch to systemd credentials: exactly what this commit does. The mkosi maintainer also expressed the possible removal of `--autologin` in the future. Pros: - Completely removes the autologin dependency on the changing mkosi behavior. Compatible with any mkosi version. - Applies to all terminals, zero hardcoded name. - Simpler, clearer and more direct implementation: zero configuration file! - More dynamic: changes and tests do not require rebuilding anything. Cons: - Requires systemd v251 or above (May 2022) - Applies to all terminals but could be more selective when using "per-instance" systemd credentials added in v257 (December 2024) Signed-off-by: Marc Herbert <[email protected]>
stellarhopper
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Feb 12, 2025
Until mkosi v24 commit c236c9f7b9c82d3, `mkosi --autologin` used to be applied to four devices: console, tty1, ttyS0 and one architecture-dependent device. mkosi has some QEMU features of its own to boot the image. run_qemu.sh never used any of that. We should probably try (some of) it in the future but I digress. In that mkosi commit, `mkosi/qemu.py` (which we don't use) stopped using `ttyS0` and replaced it with the faster `/dev/hvc0` instead. The image building code (which we DO use!) was updated correspondingly without caring about backwards compatibility and dropped ttyS0 on the floor. Someone noted this in systemd/mkosi#2834 and the recommendation was to switch to systemd credentials: exactly what this commit does. The mkosi maintainer also expressed the possible removal of `--autologin` in the future. Pros: - Completely removes the autologin dependency on the changing mkosi behavior. Compatible with any mkosi version. - Applies to all terminals, zero hardcoded name. - Simpler, clearer and more direct implementation: zero configuration file! - More dynamic: changes and tests do not require rebuilding anything. Cons: - Requires systemd v251 or above (May 2022) - Applies to all terminals but could be more selective when using "per-instance" systemd credentials added in v257 (December 2024) Signed-off-by: Marc Herbert <[email protected]>
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edk2 now has a virtio serial driver so let's switch to virtconsole
for the serial console as it's significantly faster compared to the
old ISA serial console.