Configure a serial port for a Linux VM

About this task

Perform this task to configure a serial port for a Linux VM. Before you can view console logs from the console of a VM, verify that ttyS0 in kernel boot parameter console=ttyS0,115200 already exists, which means that the VM is configured with a minimum of one serial port.

Restrictions and guidelines

• You must log in to the VM as the root user.

• If the VM uses the ARM architecture and is configured with kernel boot parameters by default, you do not need to re-configure them.

Procedure

• The following procedure uses the CentOS 6 series as an example to modify the menu.lst file of an x86 VM.

  1. Execute the following command to view the files in the /boot/grub directory:

     ls /boot/grub

  2. Execute the following command to open the /boot/grub/menu.lst file with the VI editor:

     vi /boot/grub/menu.lst

  3. Enter i to enter the edit mode.

  4. At the end of the line where the kernel parameter is located, enter a space, and then enter console=ttyS0,115200 console=tty0.

     

  5. Press ESC, enter wq, and then press Enter to save the settings and exit the editor.

  6. Restart the VM.

• The following procedure uses the CentOS 7 series as an example to modify the /default/grub file of an ARM VM.

  1. Execute the following command to view the files in the /etc/default directory:

     ls /etc/default

  2. Execute the following command to open the /etc/default/grub file with the VI editor:

     vi /etc/default/grub

  3. Enter i to enter the edit mode.

  4. Enter GRUB_CMDLINE_LINUX_DEFAULT="console=tty0 console=ttyS0,9600.

  5. Press ESC, enter wq, and then press Enter to save the settings and exit the editor.

  6. Execute the following command to update the grub2 configuration file:

     grub2-mkconfig -o /boot/grub2/grub.cfg

  7. Restart the VM.

• The following tables show the methods for configuring a serial port for different Linux operating systems:

  Table-1 Serial port configuration methods for x86 VMs

  Operating system type	Boot configuration file	Configuration method
  CentOS 5 series CentOS 6 series Red Hat Enterprise Linux 5 series Red Hat Enterprise Linux 6 series	/boot/grub/ menu.lst	Add console=ttyS0,115200 console=tty0 to the end of the kernel parameter line
  CentOS 7 series Red Hat Enterprise Linux 7 series Oracle Enterprise Linux Server 7 series Fedora series EulerOS 2.1	/boot/grub2/grub.cfg	Add console=ttyS0,115200 console=tty0 to the end of the linux16 parameter line
  SUSE Linux Enterprise Server 11 series Oracle Enterprise Linux Server 6 series	/boot/grub/menu.lst	Add console=ttyS0,115200 console=tty0 to the end of the kernel parameter line
  SUSE Linux Enterprise Server 12 series OpenSUSE 13 series OpenSUSE 42 series	/boot/grub2/grub.cfg	Add console=ttyS0,115200 console=tty0 to the end of the linux parameter line
  Debian series Ubuntu 14 series Ubuntu 16 series	/boot/grub/grub.cfg	Add console=ttyS0,115200 console=tty0 to the end of the linux parameter line
  CoreOS series	/usr/share/oem/grub.cfg	Execute the cat /proc/cmdline | grep ttyS0 command to identify whether ttyS0 is configured. If ttyS0 is not configured, configure it as follows: Find the /usr/share/oem/grub.cfg file. If the file does not exist, manually create it. Open the /usr/share/oem/grub.cfg file, and then add set linux_append="console=ttyS0,115200 console=tty0 into the file.

  Table-2 Serial port configuration methods for ARM VMs

  Operating system type	Boot configuration file	Configuration method
  CentOS 7 series Red Hat Enterprise Linux 7 series Fedora series EulerOS 2.8	/boot/grub2/grub.cfg	Add console=ttyS0,115200 console=tty0 to the end of the linux16 parameter line
  SUSE Linux Enterprise Server 12 series SUSE Linux Enterprise Server 15 series	/boot/grub2/grub.cfg	Add console=ttyS0,115200 console=tty0 to the end of the linux parameter line