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Diffstat (limited to 'docs/grub.texi')
| -rw-r--r-- | docs/grub.texi | 67 |
1 files changed, 63 insertions, 4 deletions
diff --git a/docs/grub.texi b/docs/grub.texi index 0f2ab91fc..2adfa97be 100644 --- a/docs/grub.texi +++ b/docs/grub.texi @@ -1214,10 +1214,11 @@ GRUB is configured using @file{grub.cfg}, usually located under need to write the whole thing by hand. @menu -* Simple configuration:: Recommended for most users -* Shell-like scripting:: For power users and developers -* Multi-boot manual config:: For non-standard multi-OS scenarios -* Embedded configuration:: Embedding a configuration file into GRUB +* Simple configuration:: Recommended for most users +* Root Identifcation Heuristics:: Summary on how the root file system is identified. +* Shell-like scripting:: For power users and developers +* Multi-boot manual config:: For non-standard multi-OS scenarios +* Embedded configuration:: Embedding a configuration file into GRUB @end menu @@ -1425,6 +1426,17 @@ the Linux kernel, using a @samp{root=UUID=...} kernel parameter. This is usually more reliable, but in some cases it may not be appropriate. To disable the use of UUIDs, set this option to @samp{true}. +@item GRUB_DISABLE_LINUX_PARTUUID +If @command{grub-mkconfig} cannot identify the root filesystem via its +universally-unique indentifier (UUID), @command{grub-mkconfig} can use the UUID +of the partition containing the filesystem to identify the root filesystem to +the Linux kernel via a @samp{root=PARTUUID=...} kernel parameter. This is not +as reliable as using the filesystem UUID, but is more reliable than using the +Linux device names. When @samp{GRUB_DISABLE_LINUX_PARTUUID} is set to +@samp{false}, the Linux kernel version must be 2.6.37 (3.10 for systems using +the MSDOS partition scheme) or newer. This option defaults to @samp{true}. To +enable the use of partition UUIDs, set this option to @samp{false}. + @item GRUB_DISABLE_RECOVERY If this option is set to @samp{true}, disable the generation of recovery mode menu entries. @@ -1556,6 +1568,53 @@ edit the scripts in @file{/etc/grub.d} directly. menu entries; simply type the menu entries you want to add at the end of that file, making sure to leave at least the first two lines intact. +@node Root Identifcation Heuristics +@section Root Identifcation Heuristics +If the target operating system uses the Linux kernel, @command{grub-mkconfig} +attempts to identify the root file system via a heuristic algoirthm. This +algorithm selects the identification method of the root file system by +considering three factors. The first is if an initrd for the target operating +system is also present. The second is @samp{GRUB_DISABLE_LINUX_UUID} and if set +to @samp{true}, prevents @command{grub-mkconfig} from identifying the root file +system by its UUID. The third is @samp{GRUB_DISABLE_LINUX_PARTUUID} and if set +to @samp{true}, prevents @command{grub-mkconfig} from identifying the root file +system via the UUID of its enclosing partition. If the variables are assigned +any other value, that value is considered equivalent to @samp{false}. The +variables are also considered to be set to @samp{false} if they are not set. + +When booting, the Linux kernel will delegate the task of mounting the root +filesystem to the initrd. Most initrd images determine the root file system by +checking the Linux kernel's command-line for the @samp{root} key and use its +value as the identification method of the root file system. To improve the +reliability of booting, most initrd images also allow the root file system to be +identified by its UUID. Because of this behavior, the @command{grub-mkconfig} +command will set @samp{root} to @samp{root=UUID=...} to provide the initrd with +the filesystem UUID of the root file system. + +If no initrd is detected or @samp{GRUB_DISABLE_LINUX_UUID} is set to @samp{true} +then @command{grub-command} will identify the root filesystem by setting the +kernel command-line variable @samp{root} to @samp{root=PARTUUID=...} unless +@samp{GRUB_DISABLE_LINUX_PARTUUID} is also set to @samp{true}. If +@samp{GRUB_DISABLE_LINUX_PARTUUID} is also set to @samp{true}, +@command{grub-command} will identify by its Linux device name. + +The following table summarizes the behavior of the @command{grub-mkconfig} +command. + +@multitable {detected} {GRUB_DISABLE_LINUX_PARTUUID} {GRUB_DISABLE_LINUX_UUID} {Linux Root} +@headitem Initrd detected @tab GRUB_DISABLE_LINUX_PARTUUID Set To @tab GRUB_DISABLE_LINUX_UUID Set To @tab Linux Root ID Method +@item false @tab false @tab false @tab part UUID +@item false @tab false @tab true @tab part UUID +@item false @tab true @tab false @tab dev name +@item false @tab true @tab true @tab dev name +@item true @tab false @tab false @tab fs UUID +@item true @tab false @tab true @tab part UUID +@item true @tab true @tab false @tab fs UUID +@item true @tab true @tab true @tab dev name +@end multitable + +Remember, @samp{GRUB_DISABLE_LINUX_PARTUUID} and @samp{GRUB_DISABLE_LINUX_UUID} +are also considered to be set to @samp{false} when they are unset. @node Shell-like scripting @section Writing full configuration files directly |