GRUB: Add PARTUUID Detection Support
cover GRUB: Add PARTUUID Detection Support
Hello,
This is a request to add PARTUUID detection support grub-probe for MBR and GPT partition schemes. The Linux kernel supports mounting the root filesystem by Linux device name or by the Partition [GU]UID. GRUB's mkconfig, however, currently only supports specifying the rootfs in the kernel command-line by Linux device name unless an initramfs is also present. When an initramfs is present GRUB's mkconfig will set the kernel's root parameter value to either the Linux device name or to the filesystem [GU]UID.
Therefore, the only way to protect a Linux system from failing to boot when its Linux storage device names change is to either manually edit grub.cfg or /etc/default/grub and append root=PARTUUID=xxx to the command-line or create an initramfs that understands how to mount devices by filesystem [G]UID and let grub-mkconfig pass the filesystem [GU]UID to the initramfs.
The goal of this patch set is to enable root=PARTUUID=xxx support in grub-mkconfig, so that users don't have to manually edit /etc/default/grub or grub.cfg, or create an initramfs for the sole purpose of having a robust bootloader configuration for Linux.
Thanks,
Nicholas Vinson
Nicholas Vinson (2):
Add PARTUUID detection support to grub-probe
Update grub script template files
grub-core/partmap/gpt.c | 2 ++ grub-core/partmap/msdos.c | 12 ++++++++-- include/grub/partition.h | 9 +++++++- util/grub-mkconfig.in | 2 ++ util/grub-probe.c | 58 +++++++++++++++++++++++++++++++++++++++++++++++ util/grub.d/10_linux.in | 11 +++++++-- 6 files changed, 89 insertions(+), 5 deletions(-)
Signature · 1 line
2.9.0
PATCH 1/2 Add PARTUUID detection support to grub-probe
Add PARTUUID detection to grub-probe. The grub-probe utility is used by grub-mkconfig to determine the filesystem [GU]UID, so updating it to be able to return partition [GU]UIDs seemed like the natural choice. The other obvious choice was to rely on Linux userland tools and /dev file structure which would added to the runtime dependencies of grub-probe.
--- grub-core/partmap/gpt.c | 2 ++ grub-core/partmap/msdos.c | 12 ++++++++-- include/grub/partition.h | 9 +++++++- util/grub-probe.c | 58 +++++++++++++++++++++++++++++++++++++++++++++++ 4 files changed, 78 insertions(+), 3 deletions(-)
grub-core/partmap/gpt.c +2 -0
@@ -99,6 +99,8 @@ grub_gpt_partition_map_iterate (grub_disk_t disk,if (grub_memcmp (&grub_gpt_partition_type_empty, &entry.type,sizeof (grub_gpt_partition_type_empty))) { +grub_memcpy (part.guid.gpt, entry.guid,sizeof (part.guid.gpt)); +/* Calculate the first block and the size of the partition. */ part.start =grub_le_to_cpu64 (entry.start) << sector_log; part.len = (grub_le_to_cpu64 (entry.end)
grub-core/partmap/msdos.c +10 -2
@@ -169,6 +169,13 @@ grub_partition_msdos_iterate (grub_disk_t disk,if (mbr.entries[i].flag &0x7f )return grub_error (GRUB_ERR_BAD_PART_TABLE ,"bad boot flag" ); +/* +* Copy off the NT Disk signature. Linux uses this to compute the +* PARTUUID. The disk signature is 440 bytes in and 4 bytes long. +*/ +if (p.offset ==0 ) +grub_memcpy (p.guid.mbr, mbr.code +440 ,sizeof (p.guid.mbr)); +/* Analyze DOS partitions. */ for (p.index =0 ; p.index <4 ; p.index++) {
@@ -191,7 +198,7 @@ grub_partition_msdos_iterate (grub_disk_t disk,if (!grub_msdos_partition_is_empty (e->type) && !grub_msdos_partition_is_extended (e->type)) { - p.number++; + p.guid.mbr[4 ] = ++p.number;if (hook (disk, &p, hook_data))return grub_errno;
@@ -199,7 +206,7 @@ grub_partition_msdos_iterate (grub_disk_t disk,else if (p.number <3 )/* If this partition is a logical one, shouldn't increase the partition number. */ - p.number++; + p.guid.mbr[4 ] = ++p.number; }/* Find an extended partition. */
@@ -209,6 +216,7 @@ grub_partition_msdos_iterate (grub_disk_t disk,if (grub_msdos_partition_is_extended (e->type)) { + p.guid.mbr[4 ] =4 + i;// logical partitions start with 4. p.offset = ext_offset + (grub_le_to_cpu32 (e->start) << (disk->log_sector_size -GRUB_DISK_SECTOR_BITS ));
include/grub/partition.h +8 -1
@@ -66,6 +66,13 @@ struct grub_partition/* The partition number. */ int number; +/* Unique partition GUID. */ +union + { +grub_uint8_t gpt[16 ]; +grub_uint8_t mbr[5 ]; + } guid; +/* The start sector (relative to parent). */ grub_disk_addr_t start;
@@ -84,7 +91,7 @@ struct grub_partition/* The type partition map. */ grub_partition_map_t partmap; -/* The type of partition whne it's on MSDOS. +/* The type of partition when it's on MSDOS. Used for embedding detection. */ grub_uint8_t msdostype; };
util/grub-probe.c +58 -0
76 lines not on this page · raw message
Signature · 1 line
2.9.0
PATCH 2/2 Update grub script template files
In reply to Nicholas VinsonUpdate grub-mkconfig.in and 10_linux.in to support grub-probe's new partuuid target.
--- util/grub-mkconfig.in | 2 ++ util/grub.d/10_linux.in | 11 +++++++++-- 2 files changed, 11 insertions(+), 2 deletions(-)
util/grub-mkconfig.in +2 -0
@@ -134,6 +134,7 @@ fi # Device containing our userland. Typically used for root= parameter. GRUB_DEVICE="`${grub_probe} --target=device /`" GRUB_DEVICE_UUID="`${grub_probe} --device ${GRUB_DEVICE} --target=fs_uuid 2> /dev/null`" || true +GRUB_DEVICE_PARTUUID="`${grub_probe} --device ${GRUB_DEVICE} --target=partuuid 2> /dev/null`" || true # Device containing our /boot partition. Usually the same as GRUB_DEVICE. GRUB_DEVICE_BOOT="`${grub_probe} --target=device /boot`"
@@ -182,6 +183,7 @@ if [ "x${GRUB_ACTUAL_DEFAULT}" = "xsaved" ] ; then GRUB_ACTUAL_DEFAULT="`"${grub # override them. export GRUB_DEVICE \ GRUB_DEVICE_UUID \ + GRUB_DEVICE_PARTUUID \ GRUB_DEVICE_BOOT \ GRUB_DEVICE_BOOT_UUID \ GRUB_FS \
util/grub.d/10_linux.in +9 -2
@@ -220,8 +220,15 @@ while [ "x$list" != "x" ] ; do gettext_printf "Found initrd image: %s\n" "${dirname}/${initrd}" >&2 elif test -z "${initramfs}" ; then # "UUID=" and "ZFS=" magic is parsed by initrd or initramfs. Since there's - # no initrd or builtin initramfs, it can't work here. - linux_root_device_thisversion=${GRUB_DEVICE} + # no initrd or builtin initramfs, it can't work here. However, if + # GRUB_DEVICE_PARTUUID is not empty we can use that here if + # GRUD_DISABLE_LINUX_UUID is not set to true. + if [ "x${GRUB_DISABLE_LINUX_UUID}" != "xtrue" ] + && [ "x${GRUB_DEVICE_PARTUUID}" != "x" ]; then + linux_root_device_thisversion="PARTUUID=${GRUB_DEVICE_PARTUUID}" + else + linux_root_device_thisversion=${GRUB_DEVICE} + fi fi if [ "x$is_top_level" = xtrue ] && [ "x${GRUB_DISABLE_SUBMENU}" != xy ]; then
Signature · 1 line
2.9.0
Re: [GRUB PARTUUID PATCH 2/2] Update grub script template files
Thanks,
Nicholas Vinson
---
util/grub.d/10_linux.in +1 -1
@@ -224,11 +224,11 @@ while [ "x$list" != "x" ] ; do elif test -z "${initramfs}" ; then # "UUID=" and "ZFS=" magic is parsed by initrd or initramfs. Since there's # no initrd or builtin initramfs, it can't work here. However, if # GRUB_DEVICE_PARTUUID is not empty we can use that here if # GRUD_DISABLE_LINUX_UUID is not set to true. - if [ "x${GRUB_DISABLE_LINUX_UUID}" != "xtrue" ] + if [ "x${GRUB_DISABLE_LINUX_UUID}" != "xtrue" ] \ && [ "x${GRUB_DEVICE_PARTUUID}" != "x" ]; then linux_root_device_thisversion="PARTUUID=${GRUB_DEVICE_PARTUUID}" else linux_root_device_thisversion=${GRUB_DEVICE} fi
Re: [GRUB PARTUUID PATCH 2/2] Update grub script template files
My apologies. It looks like most of my reply was cut-off when this email was sent. I'm pasting the missing part below.
Thanks,
Nicholas Vinson
Quoted 3 lines
I found a minor error in my original patch for 10_linux.in. I created the patch below to fix it. My apologies for not noticing it in the original submission.
Quoted 23 lines · Nicholas Vinson
Thanks,
Nicholas VinsonSigned-off-by Nicholas Vinson <[email protected]>---
util/grub.d/10_linux.in +1
-1@@ -224,11 +224,11 @@ while [ "x$list" != "x" ] ; do elif test -z "${initramfs}" ; then # "UUID=" and "ZFS=" magic is parsed by initrd or initramfs. Since there's # no initrd or builtin initramfs, it can't work here. However, if # GRUB_DEVICE_PARTUUID is not empty we can use that here if # GRUD_DISABLE_LINUX_UUID is not set to true. - if [ "x${GRUB_DISABLE_LINUX_UUID}" != "xtrue" ] + if [ "x${GRUB_DISABLE_LINUX_UUID}" != "xtrue" ] \ && [ "x${GRUB_DEVICE_PARTUUID}" != "x" ]; then linux_root_device_thisversion="PARTUUID=${GRUB_DEVICE_PARTUUID}" else linux_root_device_thisversion=${GRUB_DEVICE} fi
Re: [GRUB PARTUUID PATCH 1/2] Add PARTUUID detection support to grub-probe
In reply to Nicholas Vinson20.06.2016 04:37, Nicholas Vinson пишет:
Quoted 90 lines
Add PARTUUID detection to grub-probe. The grub-probe utility is used by grub-mkconfig to determine the filesystem [GU]UID, so updating it to be able to return partition [GU]UIDs seemed like the natural choice. The other obvious choice was to rely on Linux userland tools and /dev file structure which would added to the runtime dependencies of grub-probe.
Signed-off-by Nicholas Vinson <[email protected]>--- grub-core/partmap/gpt.c | 2 ++ grub-core/partmap/msdos.c | 12 ++++++++-- include/grub/partition.h | 9 +++++++- util/grub-probe.c | 58 +++++++++++++++++++++++++++++++++++++++++++++++ 4 files changed, 78 insertions(+), 3 deletions(-)grub-core/partmap/gpt.c +2
-0@@ -99,6 +99,8 @@ grub_gpt_partition_map_iterate (grub_disk_t disk,if (grub_memcmp (&grub_gpt_partition_type_empty, &entry.type,sizeof (grub_gpt_partition_type_empty))) { +grub_memcpy (part.guid.gpt, entry.guid,sizeof (part.guid.gpt)); +/* Calculate the first block and the size of the partition. */ part.start =grub_le_to_cpu64 (entry.start) << sector_log; part.len = (grub_le_to_cpu64 (entry.end)grub-core/partmap/msdos.c +10
-2@@ -169,6 +169,13 @@ grub_partition_msdos_iterate (grub_disk_t disk,if (mbr.entries[i].flag &0x7f )return grub_error (GRUB_ERR_BAD_PART_TABLE ,"bad boot flag" ); +/* +* Copy off the NT Disk signature. Linux uses this to compute the +* PARTUUID. The disk signature is 440 bytes in and 4 bytes long. +*/ +if (p.offset ==0 ) +grub_memcpy (p.guid.mbr, mbr.code +440 ,sizeof (p.guid.mbr)); +/* Analyze DOS partitions. */ for (p.index =0 ; p.index <4 ; p.index++) {@@ -191,7 +198,7 @@ grub_partition_msdos_iterate (grub_disk_t disk,if (!grub_msdos_partition_is_empty (e->type) && !grub_msdos_partition_is_extended (e->type)) { - p.number++; + p.guid.mbr[4 ] = ++p.number;if (hook (disk, &p, hook_data))return grub_errno;@@ -199,7 +206,7 @@ grub_partition_msdos_iterate (grub_disk_t disk,else if (p.number <3 )/* If this partition is a logical one, shouldn't increase the partition number. */ - p.number++; + p.guid.mbr[4 ] = ++p.number; }/* Find an extended partition. */ @@ -209,6 +216,7 @@ grub_partition_msdos_iterate (grub_disk_t disk,if (grub_msdos_partition_is_extended (e->type)) { + p.guid.mbr[4 ] =4 + i;// logical partitions start with 4. p.offset = ext_offset + (grub_le_to_cpu32 (e->start) << (disk->log_sector_size -GRUB_DISK_SECTOR_BITS ));include/grub/partition.h +7
-0@@ -66,6 +66,13 @@ struct grub_partition/* The partition number. */ int number; +/* Unique partition GUID. */ +union + { +grub_uint8_t gpt[16 ]; +grub_uint8_t mbr[5 ]; + } guid; +/* The start sector (relative to parent). */ grub_disk_addr_t start;
include/grub/partition.h struct grub_partition · line 97
Quoted 8 lines
include/grub/partition.h +1
-1@@ -84,7 +91,7 @@ struct grub_partition/* The type partition map. */ grub_partition_map_t partmap; -/* The type of partition whne it's on MSDOS. +/* The type of partition when it's on MSDOS. Used for embedding detection. */ grub_uint8_t msdostype; };
As long as this is used by grub-probe only there is no need to bloat boot time code.
Quoted 74 lines
util/grub-probe.c +51
-0@@ -62,6 +62,7 @@ enum {PRINT_DRIVE ,PRINT_DEVICE ,PRINT_PARTMAP , +PRINT_PARTUUID ,PRINT_ABSTRACTION ,PRINT_CRYPTODISK_UUID , PRINT_HINT_STR,@@ -85,6 +86,7 @@ static const char *targets[] = [PRINT_DRIVE] = "drive", [PRINT_DEVICE] = "device", [PRINT_PARTMAP] = "partmap", + [PRINT_PARTUUID] = "partuuid", [PRINT_ABSTRACTION] = "abstraction", [PRINT_CRYPTODISK_UUID] = "cryptodisk_uuid", [PRINT_HINT_STR] = "hints_string",@@ -617,6 +619,62 @@ probe (const char *path, char **device_names, char delim)else if (print ==PRINT_CRYPTODISK_UUID )probe_cryptodisk_uuid (dev->disk, delim); +else if (print ==PRINT_PARTUUID && dev->disk->partition) + { +grub_uint8_t be_guid[16 ]; +int i; +int guid_len; +if (strcmp (dev->disk->partition->partmap->name,"gpt" ) ==0 ) + { + guid_len =sizeof (dev->disk->partition->guid.gpt); +/** +* The GUID disk format is LE(4) LE(2) LE(2) BE(8). +* where LE(n) means n-bytes little-endian formatted and +* BE(n) means n-bytes big-endian formatted. +*/ +for (i =3 ; i >=0 ; i--) + { + be_guid[3 - i] = dev->disk->partition->guid.gpt[i]; + } +for (i =1 ; i >=0 ; i--) + { + be_guid[5 - i] = dev->disk->partition->guid.gpt[i +4 ]; + be_guid[7 - i] = dev->disk->partition->guid.gpt[i +6 ]; + } +for (i =7 ; i >=0 ; i--) + { + be_guid[i +8 ] = dev->disk->partition->guid.gpt[i +8 ]; + } + } +else if (strcmp (dev->disk->partition->partmap->name,"msdos" ) ==0 ) + { + guid_len =sizeof (dev->disk->partition->guid.mbr); +/* +* First 4 bytes are in LE order and need to be swapped them to BE +* order. +*/ +for (i =3 ; i >=0 ; i--) + { + be_guid[3 - i] = dev->disk->partition->guid.mbr[i]; + } +/* Adjust the last number so that it is 1-indexed. */ + be_guid[4 ] = dev->disk->partition->guid.mbr[4 ] +1 ; + } +for (i =0 ; i < guid_len; i++) + { +switch (i) + { +case 4 : +case 6 : +case 8 : +case 10 :
util/grub-probe.c probe (const char *path, char **device_names, char delim) · line 680
Quoted 10 lines
util/grub-probe.c +7
-0+printf ("-" ); +default : +printf ("%02x" , be_guid[i]); + } + } +putchar (delim); + }else if (print ==PRINT_PARTMAP )/* Check if dev->disk itself is contained in a partmap. */ probe_partmap (dev->disk, delim);
You can simply read partition table and build UUID in place. See PRINT_GPT_PARTTYPE as example.
Re: [GRUB PARTUUID PATCH 2/2] Update grub script template files
In reply to Nicholas Vinson20.06.2016 04:37, Nicholas Vinson пишет:
Quoted 35 lines
Update grub-mkconfig.in and 10_linux.in to support grub-probe's new partuuid target.
Signed-off-by Nicholas Vinson <[email protected]>--- util/grub-mkconfig.in | 2 ++ util/grub.d/10_linux.in | 11 +++++++++-- 2 files changed, 11 insertions(+), 2 deletions(-)util/grub-mkconfig.in +2
-0@@ -134,6 +134,7 @@ fi # Device containing our userland. Typically used for root= parameter. GRUB_DEVICE="`${grub_probe} --target=device /`" GRUB_DEVICE_UUID="`${grub_probe} --device ${GRUB_DEVICE} --target=fs_uuid 2> /dev/null`" || true +GRUB_DEVICE_PARTUUID="`${grub_probe} --device ${GRUB_DEVICE} --target=partuuid 2> /dev/null`" || true # Device containing our /boot partition. Usually the same as GRUB_DEVICE. GRUB_DEVICE_BOOT="`${grub_probe} --target=device /boot`"@@ -182,6 +183,7 @@ if [ "x${GRUB_ACTUAL_DEFAULT}" = "xsaved" ] ; then GRUB_ACTUAL_DEFAULT="`"${grub # override them. export GRUB_DEVICE \ GRUB_DEVICE_UUID \ + GRUB_DEVICE_PARTUUID \ GRUB_DEVICE_BOOT \ GRUB_DEVICE_BOOT_UUID \ GRUB_FS \util/grub.d/10_linux.in +0
-0@@ -220,8 +220,15 @@ while [ "x$list" != "x" ] ; do gettext_printf "Found initrd image: %s\n" "${dirname}/${initrd}" >&2
util/grub.d/10_linux.in while [ "x$list" != "x" ] ; do · line 228
Quoted 10 lines
util/grub.d/10_linux.in +6
-2elif test -z "${initramfs}" ; then # "UUID=" and "ZFS=" magic is parsed by initrd or initramfs. Since there's - # no initrd or builtin initramfs, it can't work here. - linux_root_device_thisversion=${GRUB_DEVICE} + # no initrd or builtin initramfs, it can't work here. However, if + # GRUB_DEVICE_PARTUUID is not empty we can use that here if + # GRUD_DISABLE_LINUX_UUID is not set to true. + if [ "x${GRUB_DISABLE_LINUX_UUID}" != "xtrue" ] + && [ "x${GRUB_DEVICE_PARTUUID}" != "x" ]; then + linux_root_device_thisversion="PARTUUID=${GRUB_DEVICE_PARTUUID}"
Well, PARTUUID appeared first in 2.6.37 and MSDOS "UUID" in 3.10. Unfortunately we have no way to check for it, even as fragile as stored kernel config. So I am not sure we should do it by default. And if we add some extra knob to turn it on, as you mentioned yourself, you can simply add root=PARTUUID=xxx to stored kernel command line.
One more consideration is that reinstalling in existing partition will invalidate FS UUID stored in grub.cfg which is arguably the right thing because you now have something different there, but PARTUUID will most likely remain the same.
Quoted 7 lines
util/grub.d/10_linux.in +3
-0+ else + linux_root_device_thisversion=${GRUB_DEVICE} + fi fi if [ "x$is_top_level" = xtrue ] && [ "x${GRUB_DISABLE_SUBMENU}" != xy ]; then
Re: [GRUB PARTUUID PATCH 2/2] Update grub script template files
Quoted 44 lines · Andrei Borzenkov
20.06.2016 04:37, Nicholas Vinson пишет:
Quoted 43 lines
Update grub-mkconfig.in and 10_linux.in to support grub-probe's new partuuid target.
Signed-off-by Nicholas Vinson <[email protected]>--- util/grub-mkconfig.in | 2 ++ util/grub.d/10_linux.in | 11 +++++++++-- 2 files changed, 11 insertions(+), 2 deletions(-)util/grub-mkconfig.in +2
-0@@ -134,6 +134,7 @@ fi # Device containing our userland. Typically used for root= parameter. GRUB_DEVICE="`${grub_probe} --target=device /`" GRUB_DEVICE_UUID="`${grub_probe} --device ${GRUB_DEVICE} --target=fs_uuid 2> /dev/null`" || true +GRUB_DEVICE_PARTUUID="`${grub_probe} --device ${GRUB_DEVICE} --target=partuuid 2> /dev/null`" || true # Device containing our /boot partition. Usually the same as GRUB_DEVICE. GRUB_DEVICE_BOOT="`${grub_probe} --target=device /boot`"@@ -182,6 +183,7 @@ if [ "x${GRUB_ACTUAL_DEFAULT}" = "xsaved" ] ; then GRUB_ACTUAL_DEFAULT="`"${grub # override them. export GRUB_DEVICE \ GRUB_DEVICE_UUID \ + GRUB_DEVICE_PARTUUID \ GRUB_DEVICE_BOOT \ GRUB_DEVICE_BOOT_UUID \ GRUB_FS \util/grub.d/10_linux.in +4
-2@@ -220,8 +220,15 @@ while [ "x$list" != "x" ] ; do gettext_printf "Found initrd image: %s\n" "${dirname}/${initrd}" >&2 elif test -z "${initramfs}" ; then # "UUID=" and "ZFS=" magic is parsed by initrd or initramfs. Since there's - # no initrd or builtin initramfs, it can't work here. - linux_root_device_thisversion=${GRUB_DEVICE} + # no initrd or builtin initramfs, it can't work here. However, if + # GRUB_DEVICE_PARTUUID is not empty we can use that here if + # GRUD_DISABLE_LINUX_UUID is not set to true. + if [ "x${GRUB_DISABLE_LINUX_UUID}" != "xtrue" ]
Quoted 8 lines
util/grub.d/10_linux.in while [ "x$list" != "x" ] ; do · line 228
Quoted 2 lines
util/grub.d/10_linux.in +2
-0+ && [ "x${GRUB_DEVICE_PARTUUID}" != "x" ]; then + linux_root_device_thisversion="PARTUUID=${GRUB_DEVICE_PARTUUID}"Well, PARTUUID appeared first in 2.6.37 and MSDOS "UUID" in 3.10. Unfortunately we have no way to check for it, even as fragile as stored kernel config. So I am not sure we should do it by default. And if we add some extra knob to turn it on, as you mentioned yourself, you can simply add root=PARTUUID=xxx to stored kernel command line.
I've done that using /etc/default/grub and it works, but you end up with two root=... entries in your kernel command line. I could have gone back and edited the grub.cfg to clean up the command-line.
I will adjust the logic so that using PARTUUID is an opt-in feature instead of an opt-out feature. Downstream distributions would then be able to adjust GRUB's defaults in their own packaging and turn this feature on by default if it made sense for them to do so.
Quoted 5 lines
One more consideration is that reinstalling in existing partition will invalidate FS UUID stored in grub.cfg which is arguably the right thing because you now have something different there, but PARTUUID will most likely remain the same.
I am sorry, but I am not sure I understand the issue you are raising here.
If I boot Linux without an initramfs, I must specify where the root partition (or device, if the device has no partitions) is. GRUB currently does this by setting root to something like '/dev/sda3'. That said, this is a Linux limitation not GRUB's. Linux is unable to use the FS UUID this early in the boot process.
If I have an initramfs, I *may* be able to use the FS UUID. In this case, it all depends on the implementation of my initramfs. However, GRUB's current behavior is to assume that all initramfs implementations understand how to handle UUIDs, that the UUID is the FS UUID, and are able to mount rootfs properly.
I have no interest in debating if that behavior is correct or not, nor do I have any interest in changing it. As currently written, my patch should favor the FS UUID when an initramfs is detected, the PARTUUID when it is not, and the Linux device naming scheme when the UUID feature is disabled or the PARTUUID could not be found.
The rationale for favoring PARTUUID over the linux device name is because the PARTUUID would allow a system to boot if the device with the root partition is ever renamed. In other words, if the device was sda when grub.cfg was created, but somehow became sdb (or the other way around), the system would sill be able to boot because the kernel would still be able to find /sbin/init. Whereas with the linux device name, the boot would fail because it would be looking at the wrong device for /sbin/init (FS UUID provides the same protections, but in theory allows use to reorder partitions on a single device and still boot successfully without having to regenerate the grub.cfg).
If there is something I am missing, let me know, so I can address it.
Thanks,
Nicholas Vinson
Quoted 9 lines
Quoted 8 lines
util/grub.d/10_linux.in +3
-0+ else + linux_root_device_thisversion=${GRUB_DEVICE} + fi fi if [ "x$is_top_level" = xtrue ] && [ "x${GRUB_DISABLE_SUBMENU}" != xy ]; then