Why does grub2-mkconfig command not reflect configuration change in /etc/default/grub?

Solution Verified - Updated

Environment

  • Red Hat Enterprise Linux 7
  • grub2

Issue

  • Why does grub2-mkconfig command not reflect configuration change in /etc/default/grub?

  • There are multiple same parameters in /etc/default/grub. The latest parameter is only affected.

    $ /cat etc/default/grub 
GRUB_TIMEOUT=5
GRUB_DEFAULT=1
GRUB_DISABLE_SUBMENU=true
GRUB_TERMINAL_OUTPUT="console"
GRUB_CMDLINE_LINUX="crashkernel=512M"  <--- This option is not present on boot line
GRUB_DISABLE_RECOVERY="true"
GRUB_CMDLINE_LINUX="audit=1"           <--- This option is only one present at boot time

Resolution

  • This is an expected behavior. If there exist multiple same parameters, the latest one is only reflected. Because grub2-mkconfig command is a shell script. The last parameter in duplicate parameters is valid.
    The parameters need to be consolidated in each line. For example,

    • Invalid configuration.

      
$ /cat etc/default/grub 
      
GRUB_TIMEOUT=5
      
GRUB_DEFAULT=1
      
GRUB_DISABLE_SUBMENU=true
      
GRUB_TERMINAL_OUTPUT="console"
      
GRUB_CMDLINE_LINUX="crashkernel=512M"  <--- This line is not used, is replaced by...
      
GRUB_DISABLE_RECOVERY="true"
      
GRUB_CMDLINE_LINUX="audit=1"           <--- by this line, the last GRUB_CMDLINE_LINUX instance

    • Valid configuration

      
$ /cat etc/default/grub 
      
GRUB_TIMEOUT=5
      
GRUB_DEFAULT=1
      
GRUB_DISABLE_SUBMENU=true
      
GRUB_TERMINAL_OUTPUT="console"
      
GRUB_CMDLINE_LINUX="crashkernel=512M audit=1"  <--- The line is merged and properly handled.
      
GRUB_DISABLE_RECOVERY="true"

Root Cause

  • /etc/default/grub file is used by grub2-mkconfig command which is a shell script. These parameters need to be aligned with bash grammar.
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