I have this problem on more than one host, so the specific hardware is not an issue.

Bare metal Ubuntu 12 is not creating a login process on the only serial port, in the default configuration. The serial port works correctly with the firmware. It works correctly with Grub2. I have even connected the serial line to 2 different external client boxes, so the problem is neither the hardware nor the remote client.

When finally booted, the system fails to create the login process.

root@xenpro3:~# ps ax | grep tty

  1229 tty4     Ss+    0:00 /sbin/getty -8 38400 tty4

  1233 tty5     Ss+    0:00 /sbin/getty -8 38400 tty5

  1239 tty2     Ss+    0:00 /sbin/getty -8 38400 tty2

  1241 tty3     Ss+    0:00 /sbin/getty -8 38400 tty3

  1245 tty6     Ss+    0:00 /sbin/getty -8 38400 tty6

  1403 tty1     Ss+    0:00 /sbin/getty -8 38400 tty1

  1996 pts/0    S+     0:00 grep --color=auto tty

root@xenpro3:~# dmesg | grep tty

[    0.000000] Command line: BOOT_IMAGE=/vmlinuz-3.2.0-30-generic root=/dev/mapper/xenpro3-root ro console=ttyS0,115200n8

[    0.000000] Kernel command line: BOOT_IMAGE=/vmlinuz-3.2.0-30-generic root=/dev/mapper/xenpro3-root ro console=ttyS0,115200n8

[    0.000000] console [ttyS0] enabled

[    2.160986] serial8250: ttyS0 at I/O 0x3f8 (irq = 4) is a 16550A

[    2.203396] serial8250: ttyS1 at I/O 0x2f8 (irq = 3) is a 16550A

[    2.263296] 00:08: ttyS0 at I/O 0x3f8 (irq = 4) is a 16550A

[    2.323102] 00:09: ttyS1 at I/O 0x2f8 (irq = 3) is a 16550A

root@xenpro3:~# uname -a

Linux xenpro3 3.2.0-30-generic #48-Ubuntu SMP Fri Aug 24 16:52:48 UTC 2012 x86_64 x86_64 x86_64 GNU/Linux

root@xenpro3:~# 

I have tried putting a ttyS0.conf file in /etc/initab, which solves the problem bare metal but I still cannot get the serial port to work when booting Ubuntu on top of Xen, as domain 0. My serial line output looks like this, when booting Xen

/dev/ttyS0 at 0x03f8 (irq = 4) is a 16550A

 * Exporting directories for NFS kernel daemon...                        [ OK ] 

 * Starting NFS kernel daemon                                            [ OK ] 
SSL tunnels disabled, see /etc/default/stunnel4

[   18.654627] XENBUS: Unable to read cpu state

[   18.659631] XENBUS: Unable to read cpu state

[   18.664398] XENBUS: Unable to read cpu state

[   18.669248] XENBUS: Unable to read cpu state

 * Starting Xen daemons 
                                                 [ OK ] 
mountall: Disconnected from Plymouth

At this point, the serial line is no longer connected to a process. Xen itself is running just fine. Dmesg gives me a long list of

[  120.236841] init: ttyS0 main process ended, respawning

[  120.239717] ttyS0: LSR safety check engaged!

[  130.240265] init: ttyS0 main process (1631) terminated with status 1

[  130.240294] init: ttyS0 main process ended, respawning

[  130.242970] ttyS0: LSR safety check engaged!

which is no surprise because I see

root@xenpro3:~# ls -l /dev/ttyS?

crw-rw---- 1 root tty     4, 64 Nov  7 14:04 /dev/ttyS0

crw-rw---- 1 root dialout 4, 65 Nov  7 14:04 /dev/ttyS1

crw-rw---- 1 root dialout 4, 66 Nov  7 14:04 /dev/ttyS2

crw-rw---- 1 root dialout 4, 67 Nov  7 14:04 /dev/ttyS3

crw-rw---- 1 root dialout 4, 68 Nov  7 14:04 /dev/ttyS4

crw-rw---- 1 root dialout 4, 69 Nov  7 14:04 /dev/ttyS5

crw-rw---- 1 root dialout 4, 70 Nov  7 14:04 /dev/ttyS6

crw-rw---- 1 root dialout 4, 71 Nov  7 14:04 /dev/ttyS7

crw-rw---- 1 root dialout 4, 72 Nov  7 14:04 /dev/ttyS8

crw-rw---- 1 root dialout 4, 73 Nov  7 14:04 /dev/ttyS9

If I manually change the group of /dev/ttyS0 to dialout, it gets changed back. I have made no changes to the default udev rules, so I cannot see where this problem is coming from.

Sincerely,

John