Public bug reported: I ran into a problem with the console argument handling on a physical system with a BMC (Dell R610) and also reproduced the same behavior on a QEMU/KVM VM with multiple serial ports.
The kernel documentation notes that the last entry will https://www.kernel.org/doc/Documentation/ABI/testing/sysfs-tty "What: /sys/class/tty/console/active Shows the list of currently configured console devices, like 'tty1 ttyS0'. The last entry in the file is the active device connected to /dev/console. The file supports poll() to detect virtual console switches." https://elixir.bootlin.com/linux/v4.15.18/source/kernel/printk/printk.c#L1960 "The last preferred console added will be used for kernel messages and stdin/out/err for init." The actual behavior is different and the console specified in the last console argument does not become an active one. As a result, SOL functionality is not possible to use unless only one ttyS<n> argument is specified in the kernel command line arguments. Setting the arguments to only contain the right one results in a proper behavior and I can see rx counters increasing in /proc/tty/driver/serial for the relevant port after I type something via the BMC. $ cat /proc/cmdline BOOT_IMAGE=/vmlinuz-4.15.0-42-generic root=UUID=580a3c58-1040-4c7d-b94f-93230874caf5 ro console=tty0 console=ttyS0,115200 console=ttyS1,115200 journalctl -k | grep ttyS Dec 03 21:42:41 ubuntu kernel: Command line: BOOT_IMAGE=/vmlinuz-4.15.0-42-generic root=UUID=580a3c58-1040-4c7d-b94f-93230874caf5 ro console=tty0 console=ttyS0,115200 console=ttyS1,115200 Dec 03 21:42:41 ubuntu kernel: Kernel command line: BOOT_IMAGE=/vmlinuz-4.15.0-42-generic root=UUID=580a3c58-1040-4c7d-b94f-93230874caf5 ro console=tty0 console=ttyS0,115200 console=ttyS1,115200 Dec 03 21:42:41 ubuntu kernel: console [ttyS0] enabled Dec 03 21:42:41 ubuntu kernel: 00:02: ttyS0 at I/O 0x3f8 (irq = 4, base_baud = 115200) is a 16550A Dec 03 21:42:41 ubuntu kernel: 00:03: ttyS1 at I/O 0x2f8 (irq = 3, base_baud = 115200) is a 16550A Dec 03 21:42:41 ubuntu kernel: tty ttyS3: hash matches Full dmesg: http://paste.ubuntu.com/p/bV2pDc4Hdw/ $ cat /sys/class/tty/console/active ttyS0 tty0 $ sudo cat /proc/tty/driver/serial serinfo:1.0 driver revision: 0: uart:16550A port:000003F8 irq:4 tx:78 rx:0 RTS|DTR 1: uart:16550A port:000002F8 irq:3 tx:0 rx:0 CTS|DSR|CD 2: uart:unknown port:000003E8 irq:4 3: uart:unknown port:000002E8 irq:3 # ... ~~~ GRUB setttings: # the ones that override /etc/default/grub $ cat /etc/default/grub.d/50-curtin-settings.cfg cat: cat: No such file or directory GRUB_CMDLINE_LINUX_DEFAULT="console=tty0 console=ttyS0,115200 console=ttyS1,115200" # disable grub os prober that might find other OS installs. GRUB_DISABLE_OS_PROBER=true GRUB_TERMINAL=console /etc/default/grub: https://paste.ubuntu.com/p/sdWQrY7JwN/ # grub.cfg: http://paste.ubuntu.com/p/zKGTqDh6sR/ # two entries, both with the proper arg and properly sent to the kernel cmdline based on /proc/cmdline grep ttyS grub.cfg linux /vmlinuz-4.15.0-42-generic root=UUID=580a3c58-1040-4c7d-b94f-93230874caf5 ro console=tty0 console=ttyS0,115200 console=ttyS1,115200 linux /vmlinuz-4.15.0-42-generic root=UUID=580a3c58-1040-4c7d-b94f-93230874caf5 ro console=tty0 console=ttyS0,115200 console=ttyS1,115200 ~~~ I managed to reproduce the exact same behavior on a VM with multiple 8250 serial ports. ubuntu@maas-vhost5:~$ cat /sys/class/tty/console/active ttyS0 ubuntu@maas-vhost5:~$ cat /proc/cmdline BOOT_IMAGE=/boot/vmlinuz-4.15.0-42-generic root=UUID=a60217c2-6752-4c69-afb9-55f86a2b6c1d ro console=ttyS0,115200 console=ttyS2,115200 console=ttyS1,115200 ubuntu@maas-vhost5:~$ grep -RP ttyS /boot/grub/grub.cfg linux /boot/vmlinuz-4.15.0-42-generic root=UUID=a60217c2-6752-4c69-afb9-55f86a2b6c1d ro console=ttyS0,115200 console=ttyS2,115200 console=ttyS1,115200 linux /boot/vmlinuz-4.15.0-42-generic root=UUID=a60217c2-6752-4c69-afb9-55f86a2b6c1d ro console=ttyS0,115200 console=ttyS2,115200 console=ttyS1,115200 linux /boot/vmlinuz-4.15.0-39-generic root=UUID=a60217c2-6752-4c69-afb9-55f86a2b6c1d ro console=ttyS0,115200 console=ttyS2,115200 console=ttyS1,115200 # changed to the following config with only ttyS1 present: ubuntu@maas-vhost5:~$ grep -RP ttyS /boot/grub/grub.cfg linux /boot/vmlinuz-4.15.0-42-generic root=UUID=a60217c2-6752-4c69-afb9-55f86a2b6c1d ro console=ttyS1,115200 linux /boot/vmlinuz-4.15.0-42-generic root=UUID=a60217c2-6752-4c69-afb9-55f86a2b6c1d ro console=ttyS1,115200 linux /boot/vmlinuz-4.15.0-39-generic root=UUID=a60217c2-6752-4c69-afb9-55f86a2b6c1d ro console=ttyS1,115200 # 1 tty passed only ubuntu@maas-vhost5:~$ cat /proc/cmdline BOOT_IMAGE=/boot/vmlinuz-4.15.0-42-generic root=UUID=a60217c2-6752-4c69-afb9-55f86a2b6c1d ro console=ttyS1,115200 # now it's shown as active ubuntu@maas-vhost5:~$ cat /sys/class/tty/console/active ttyS1 ubuntu@maas-vhost5:~$ sudo cat /proc/tty/driver/serial serinfo:1.0 driver revision: 0: uart:16550A port:000003F8 irq:4 tx:0 rx:0 CTS|DSR|CD 1: uart:16550A port:000002F8 irq:3 tx:14763 rx:0 RTS|CTS|DTR|DSR|CD 2: uart:16550A port:000003E8 irq:4 tx:0 rx:0 CTS|DSR|CD ~~~~ Relevant code: https://elixir.bootlin.com/linux/v4.15.18/source/kernel/printk/printk.c#L2379 https://elixir.bootlin.com/linux/v4.15.18/source/kernel/printk/printk.c#L1916 https://elixir.bootlin.com/linux/v4.15.18/source/kernel/printk/printk.c#L1961 https://elixir.bootlin.com/linux/v4.15.18/source/kernel/printk/printk.c#L1886 ** Affects: linux (Ubuntu) Importance: Undecided Status: New ** Tags: cpe-onsite -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1807140 Title: The last console= argument is not used by the kernel To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1807140/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
