Oracle Cloud Infrastructure Documentation

Managing Kernels for Oracle Linux Instances

Learn how to manage kernel boot parameters before booting and at runtime and how to use grubby to manage kernels for Oracle Linux instances on Oracle Cloud Infrastructure.

See also: Managing Kernels and System Boot.

Using grubby to Manage Kernels

The grubby tool can be used to read information from and make persistent changes to the grub.cfg file which defines the GRUB configuration for an Oracle Linux instance. Using the grubby command, you can view kernel configuration, specify the default boot kernel, configure extra kernel command line boot parameters, and change the kernel boot (GRUB) menu. See the grubby(8) manual page for more information.

List Installed Kernels and Default Kernel

Use the grubby command to see all kernels installed on an Oracle Linux instance, configuration information about the kernels, which kernel is the default and which kernel is currently running.

  1. From a command line, using administrative privileges connect to the instance using SSH.
  2. List the installed kernels using one of the following options. The list of installed kernels might be different depending on the Oracle Linux version.
    • List the kernels using grubby and the --info=ALL command option to see the boot configuration associated with each installed kernel.
      sudo grubby --info=ALL
      index=0 <<Each boot entry is assigned an index, which is a number that indicates its position in the GRUB menu
kernel="/boot/vmlinuz-5.15.0-305.176.4.el8uek.x86_64" <<Full path to the kernel image
args="ro crashkernel=auto LANG=en_US.UTF-8 console=tty0 console=ttyS0,115200 rd.luks=0 / <<Command-line arguments passed to the kernel when it boots
      rd.md=0 rd.dm=0 rd.lvm.vg=ocivolume rd.lvm.lv=ocivolume/root rd.net.timeout.carrier=5 /
      netroot=iscsi:169.254.0.2:::1:iqn.2015-02.oracle.boot:uefi /
      rd.iscsi.param=node.session.timeo.replacement_timeout=6000 net.ifnames=1 /
      nvme_core.shutdown_timeout=10 ipmi_si.tryacpi=0 ipmi_si.trydmi=0 libiscsi.debug_libiscsi_eh=1 /   
      loglevel=4 ip=dhcp,dhcp6 rd.net.timeout.dhcp=10 crash_kexec_post_notifiers /
      fips=1 boot=UUID=5097b6ba-ed0e-418a-9c2c-fb25d577991f $tuned_params"
root="/dev/mapper/ocivolume-root" <<Root partition device
initrd="/boot/initramfs-5.15.0-305.176.4.el8uek.x86_64.img $tuned_initrd" <<Path to the initial RAM disk (initrd) image
title="Oracle Linux Server (5.15.0-305.176.4.el8uek.x86_64 with Unbreakable Enterprise Kernel) 8.10" <<Title displayed in the GRUB menu at startup
id="7063910fe2979258f8fd66f2fb8b8567-5.15.0-305.176.4.el8uek.x86_64" <<Unique identifier for the boot entry

index=1
kernel="/boot/vmlinuz-4.18.0-553.40.1.el8_10.x86_64"
...
title="Oracle Linux Server (4.18.0-553.40.1.el8_10.x86_64) 8.10"
...

index=2
kernel="/boot/vmlinuz-0-rescue-7063910fe2979258f8fd66f2fb8b8567"
...
title="Oracle Linux Server (0-rescue-7063910fe2979258f8fd66f2fb8b8567 with Unbreakable Enterprise Kernel) 8.10"
...

      From the output of sudo grubby --info=ALL, you can determine what is displayed in kernel boot menu at startup. For example, using the index number and title in the above output, the kernel boot menu would display as follows: 

      Oracle Linux Server (5.15.0-305.176.4.el8uek.x86_64 with Unbreakable Enterprise Kernel) 8.10
Oracle Linux Server (4.18.0-553.40.1.el8_10.x86_64) 8.10
Oracle Linux Server (0-rescue-7063910fe2979258f8fd66f2fb8b8567 with Unbreakable Enterprise Kernel) 8.10
    • List the installed kernels in the /boot directory.
      sudo ls -l /boot/vmlinuz*
      -rwxr-xr-x. 1 root root 13701352 Feb 12 19:33 /boot/vmlinuz-0-rescue-7063910fe2979258f8fd66f2fb8b8567
-rwxr-xr-x. 1 root root 10889384 Feb 11 12:19 /boot/vmlinuz-4.18.0-553.40.1.el8_10.x86_64
-rwxr-xr-x. 1 root root 13701352 Jan 29 04:13 /boot/vmlinuz-5.15.0-305.176.4.el8uek.x86_64
  3. List which kernel is configured as the default kernel to use at boot and its title and position as seen in the kernel boot menu. The default kernel might be different depending on the Oracle Linux version.
    • List default kernel.
      sudo grubby --default-kernel
      /boot/vmlinuz-5.15.0-305.176.4.el8uek.x86_64
    • Check the title of the default kernel.
      sudo grubby --default-title

      The output matches the value seen in the kernel boot menu when starting Oracle Linux 

      Oracle Linux Server (5.15.0-305.176.4.el8uek.x86_64 with Unbreakable Enterprise Kernel) 8.10
    • Find the position of the default kernel in the kernel boot list.
      sudo grubby --default-index
      0
  4. Check which kernel is currently running on the instance. 
    uname -r
    5.15.0-305.176.4.el8uek.x86_64

    The default kernel and the currently running kernel might not be identical because

    • You installed a newer kernel, but you have not rebooted the system
    • During a system reboot, you selected an alternative kernel manually to be the operative kernel
    • You manually updated the default kernel but have not rebooted the system after the update

Change Default Kernel

Use the grubby command to set the default boot kernel in the GRUB 2 configuration.

  1. From a command line, using administrative privileges connect to the instance using SSH.
  2. List default kernel.
    sudo grubby --default-kernel

    For example:

    /boot/vmlinuz-5.15.0-305.176.4.el8uek.x86_64
  3. Use the grubby --set-default command to change the default kernel making sure to specify the full path to the kernel. You can get the kernel path using either of the options in step 2 of Listing Installed Kernels and Default Kernel.

    For example:

    sudo grubby --set-default /boot/vmlinuz-4.18.0-553.40.1.el8_10.x86_64

    The change takes effect immediately and persists across system reboots.

  4. Verify the default kernel change.
    sudo grubby --default-kernel

    For example:

    /boot/vmlinuz-4.18.0-553.40.1.el8_10.x86_64
  5. (Optional) Set the new default kernel to the first position in the kernel boot menu using the grubby --set-default-index command.
    sudo grubby --set-default-index=0
    The new default kernel is displayed first in the kernel boot menu, for example:
    Oracle Linux Server (4.18.0-553.40.1.el8_10.x86_64) 8.10
Oracle Linux Server (5.15.0-305.176.4.el8uek.x86_64 with Unbreakable Enterprise Kernel) 8.10
Oracle Linux Server (0-rescue-7063910fe2979258f8fd66f2fb8b8567 with Unbreakable Enterprise Kernel) 8.10
  6. Reboot the instance to boot with the new default kernel.

Change Kernel Boot Parameters

Use the grubby --update-kernel command to add new arguments, change existing argument values, or remove arguments for a specific kernel or all kernels. Multiple arguments can be specified for each option in a quoted space-separated list. You can add and remove arguments in the same operation. When using the --args option, if an argument already exists the new value replaces the old values.

  1. From a command line, using administrative privileges connect to the instance using SSH.
  2. Use the grubby --update-kernel command to change or add a specific kernel boot argument. For example, update the kernel parameters to change the LANG argument for:
    • all kernels
      sudo grubby --update-kernel=ALL --args LANG=en_GB.UTF-8
    • one kernel
       sudo grubby --update-kernel /boot/vmlinuz-5.4.17-2136.337.5.1.el7uek.x86_64 --args LANG=en_GB.UTF-8
  3. Verify the changes have taken effect.
    sudo grubby --info=ALL
    • all kernels
      index=0
kernel="/boot/vmlinuz-5.4.17-2136.337.5.1.el7uek.x86_64"
args="ro crashkernel=auto console=tty0 console=ttyS0,115200 rd.luks=0 rd.md=0 
   rd.dm=0 rd.lvm.vg=ocivolume rd.lvm.lv=ocivolume/root rd.net.timeout.carrier=5 
   netroot=iscsi:169.254.0.2:::1:iqn.2015-02.oracle.boot:uefi 
   rd.iscsi.param=node.session.timeo.replacement_timeout=6000 
   net.ifnames=1 nvme_core.shutdown_timeout=10 ipmi_si.tryacpi=0 ipmi_si.trydmi=0 
   libiscsi.debug_libiscsi_eh=1 loglevel=4 ip=dhcp,dhcp6 rd.net.timeout.dhcp=10   
   crash_kexec_post_notifiers fips=1 boot=UUID=5097b6ba-ed0e-418a-9c2c-fb25d577991f 
   LANG=en_GB.UTF-8 $tuned_params"
...
index=1
kernel="/boot/vmlinuz-4.18.0-553.40.1.el8_10.x86_64"
args="ro crashkernel=auto console=tty0 console=ttyS0,115200 rd.luks=0 rd.md=0 
   rd.dm=0 rd.lvm.vg=ocivolume rd.lvm.lv=ocivolume/root rd.net.timeout.carrier=5 
   netroot=iscsi:169.254.0.2:::1:iqn.2015-02.oracle.boot:uefi 
   rd.iscsi.param=node.session.timeo.replacement_timeout=6000 net.ifnames=1 
   nvme_core.shutdown_timeout=10 ipmi_si.tryacpi=0 ipmi_si.trydmi=0 libiscsi.debug_libiscsi_eh=1 
   loglevel=4 ip=dhcp,dhcp6 rd.net.timeout.dhcp=10 crash_kexec_post_notifiers 
   fips=1 boot=UUID=5097b6ba-ed0e-418a-9c2c-fb25d577991f 
   LANG=en_GB.UTF-8 $tuned_params"
...
    • one kernel
      index=0
kernel="/boot/vmlinuz-5.4.17-2136.337.5.1.el7uek.x86_64"
args="ro crashkernel=auto console=tty0 console=ttyS0,115200 rd.luks=0 rd.md=0 
   rd.dm=0 rd.lvm.vg=ocivolume rd.lvm.lv=ocivolume/root rd.net.timeout.carrier=5 
   netroot=iscsi:169.254.0.2:::1:iqn.2015-02.oracle.boot:uefi 
   rd.iscsi.param=node.session.timeo.replacement_timeout=6000 
   net.ifnames=1 nvme_core.shutdown_timeout=10 ipmi_si.tryacpi=0 ipmi_si.trydmi=0 
   libiscsi.debug_libiscsi_eh=1 loglevel=4 ip=dhcp,dhcp6 rd.net.timeout.dhcp=10   
   crash_kexec_post_notifiers fips=1 boot=UUID=5097b6ba-ed0e-418a-9c2c-fb25d577991f 
   LANG=en_GB.UTF-8 $tuned_params"
...
index=1
kernel="/boot/vmlinuz-4.18.0-553.40.1.el8_10.x86_64"
args="ro crashkernel=auto console=tty0 console=ttyS0,115200 rd.luks=0 rd.md=0 
   rd.dm=0 rd.lvm.vg=ocivolume rd.lvm.lv=ocivolume/root rd.net.timeout.carrier=5 
   netroot=iscsi:169.254.0.2:::1:iqn.2015-02.oracle.boot:uefi 
   rd.iscsi.param=node.session.timeo.replacement_timeout=6000 net.ifnames=1 
   nvme_core.shutdown_timeout=10 ipmi_si.tryacpi=0 ipmi_si.trydmi=0 libiscsi.debug_libiscsi_eh=1 
   loglevel=4 ip=dhcp,dhcp6 rd.net.timeout.dhcp=10 crash_kexec_post_notifiers 
   fips=1 boot=UUID=5097b6ba-ed0e-418a-9c2c-fb25d577991f 
   LANG=en_US.UTF-8 $tuned_params"
...
  4. Reboot the instance to boot with the new kernel configuration.
Tip

To change kernel boot parameters without grubby, edit the /etc/default/grub file directly and modify boot parameter settings in the GRUB_CMDLINE_LINUX definition. For example, change LANG=en_US.UTF-8 to LANG=en_GB.UTF-8:
GRUB_CMDLINE_LINUX="crashkernel=auto LANG=en_GB.UTF-8 console=tty0 console=ttyS0
,115200 rd.luks=0 rd.md=0 rd.dm=0 rd.lvm.vg=ocivolume rd.lvm.lv=ocivolume/root r
d.net.timeout.carrier=5 netroot=iscsi:169.254.0.2:::1:iqn.2015-02.oracle.boot:ue
fi rd.iscsi.param=node.session.timeo.replacement_timeout=6000 net.ifnames=1 nvme
_core.shutdown_timeout=10 ipmi_si.tryacpi=0 ipmi_si.trydmi=0 libiscsi.debug_libi
scsi_eh=1 loglevel=4 ip=dhcp,dhcp6 rd.net.timeout.dhcp=10 crash_kexec_post_notif
iers"
For the changes to take effect at the next system reboot, rebuild the GRUB 2 configuration: 
sudo grub2-mkconfig -o /boot/grub2/grub.cfg