I have 2 (soon to be more) independent OSes. Right now it is just CentOS 6.6 and 7, but will be adding several more.I can boot CentOS 7 cleanly, but 6.6 will not boot. The error is:error: no such device (long UUID here)error: unknown filesystemFYI, the disk is GPT, partitioned with gdisk/parted. There is a /boot for 7 on /dev/sda2 and another one for 6.6 on /dev/sda9. Both have the full /boot/grub2/ directory (not that it should matter), and identical grub2.cfg. The working 7 one (sda2) is formatted xfs. The unsuccessful 6.6 one (sda9) fails with ext2, ext4 or xfs. Going into grub command-line, I try to list the partitions. It sees all of the partitions, but cannot see a filesystem on anything but sda2:grub> ls (hd0,2)      Partition hd0,2: Filesystem type xfs, UUID 97df.... - Partition start at 2048 KiB - Total size 512000 KiBgrub> ls (hd0,9)      Partition hd0,9: No known filesystem detected - Partition start at 279393720 KiB - Total size 495616 KiBBooting into 7, I can mount sda9 directly, all looks good.Partition table from parted:(parted) pModel: DELL PERC H730 Mini (scsi)Disk /dev/sda: 8397GBSector size (logical/physical): 512B/512BPartition Table: gptDisk Flags:Number  Start   End     Size    File system  Name            Flags 1      1049kB  2097kB  1049kB                               bios_grub 2      2097kB  526MB   524MB   xfs 3      526MB   537GB   537GB                                lvm 4      537GB   1074GB  537GB                                lvm 5      1074GB  1504GB  430GB                                lvm 6      1504GB  1933GB  430GB                                lvm 7      1933GB  2324GB  391GB                                lvm 8      2324GB  2861GB  537GB                Linux LVM       lvm 9      2861GB  2861GB  508MB   xfs          centos_66_boot10      2861GB  2961GB  99.5GB               centos_66_root  lvm11      2961GB  2971GB  9999MB               smart_data112      2971GB  3071GB  100GB                smart_data2(nothing on the smart_* partitions, to be used for alternate app stuff).If you prefer from gdisk:Disk /dev/sda: 16401301504 sectors, 7.6 TiBLogical sector size: 512 bytesDisk identifier (GUID): 5B41D43E-6D17-4E34-9068-E66BD3753D70Partition table holds up to 128 entriesFirst usable sector is 34, last usable sector is 16401301470Partitions will be aligned on 2048-sector boundariesTotal free space is 10403256253 sectors (4.8 TiB)Number  Start (sector)    End (sector)  Size       Code  Name   1            2048            4095   1024.0 KiB  EF02   2            4096         1028095   500.0 MiB   0700   3         1028096      1049612287   500.0 GiB   8E00   4      1049612288      2098196479   500.0 GiB   8E00   5      2098196480      2937065471   400.0 GiB   8E00   6      2937065472      3775934463   400.0 GiB   8E00   7      3775934464      4539299839   364.0 GiB   8E00   8      4539299840      5587875839   500.0 GiB   8E00  Linux LVM   9      5587875840      5588867071   484.0 MiB   0700  centos_66_boot  10      5588867072      5783203839   92.7 GiB    8E00  centos_66_root  11      5783203840      5802733567   9.3 GiB     0700  smart_boot  12      5802733568      5998047231   93.1 GiB    BF00  smart_dataRelevant parts of /boot/grub2/grub.cfg:menuentry 'CentOS Linux 7 (Core), with Linux 3.10.0-229.14.1.el7.x86_64' --class rhel fedora --class gnu-linux --class gnu --class os --unrestricted $menuentry_id_option 'gnulinux-3.10.0-229.14.1.el7.x86_64-advanced-d171cb6d-c39b-45d5-b09a-33f641c3f397' {        load_video        set gfxpayload=keep        insmod gzio        insmod part_gpt        insmod xfs        set root='hd0,gpt2'        if [ x$feature_platform_search_hint = xy ]; then          search --no-floppy --fs-uuid --set=root --hint-bios=hd0,gpt2 --hint-efi=hd0,gpt2 --hint-baremetal=ahci0,gpt2 --hint='hd0,gpt2'  97dfd142-3423-459a-a39e-9a6099b3e5fc        else          search --no-floppy --fs-uuid --set=root 97dfd142-3423-459a-a39e-9a6099b3e5fc        fi        linux16 /vmlinuz-3.10.0-229.14.1.el7.x86_64 root=/dev/mapper/root-lv_root ro rd.lvm.lv=root/lv_root rd.lvm.lv=centos/swap crashkernel=auto rhgb quiet        initrd16 /initramfs-3.10.0-229.14.1.el7.x86_64.img}    menuentry 'CentOS release 6.6 (Final) (on /dev/mapper/vg_centos6-lv_centos6_root)' --class gnu-linux --class gnu --class os $menuentry_id_option 'osprober-gnulinux-simple-b5002a5f-a521-423c-bae5-82e0aefe5e17' {        insmod part_gpt        insmod xfs        set root='hd0,gpt9'        if [ x$feature_platform_search_hint = xy ]; then          search --no-floppy --fs-uuid --set=root --hint-bios=hd0,gpt9 --hint-efi=hd0,gpt9 --hint-baremetal=ahci0,gpt9 --hint='hd0,gpt9'  5715cdc8-9d49-49c3-814f-eb887d69b7d4        else          search --no-floppy --fs-uuid --set=root 5715cdc8-9d49-49c3-814f-eb887d69b7d4        fi        linux /vmlinuz-2.6.32-504.el6.x86_64 root=/dev/dm-5        initrd /initramfs-2.6.32-504.el6.x86_64.img}I also tried alternate partition codes for sda9, nothing works. What am I missing?For what it's worth, grub2 version:# rpm -qi grub2Name        : grub2Epoch       : 1Version     : 2.02Release     : 0.17.0.1.el7.centos.4Architecture: x86_64Install Date: Mon 26 Oct 2015 05:48:42 PM ISTGroup       : System Environment/BaseSize        : 7394739License     : GPLv3+Signature   : RSA/SHA256, Wed 23 Sep 2015 07:13:19 PM IDT, Key ID 24c6a8a7f4a80eb5Source RPM  : grub2-2.02-0.17.0.1.el7.centos.4.src.rpmBuild Date  : Wed 23 Sep 2015 05:51:07 PM IDTBuild Host  : kbuilder.dev.centos.orgRelocations : (not relocatable)URL         : http://www.gnu.org/software/grub/Summary     : Bootloader with support for Linux, Multiboot and moreAt request of commenter, output:# file -s /dev/sda9/dev/sda9: SGI XFS filesystem data (blksz 4096, inosz 256, v2 dirs)# file -s /dev/sda2/dev/sda2: SGI XFS filesystem data (blksz 4096, inosz 256, v2 dirs)And grub2-probe seems content with both:# grub2-probe --device /dev/sda2xfs# grub2-probe --device /dev/sda9xfsgrub2-fstest also seems to return cleanly for those partitions:# grub2-fstest -vvv -r /dev/sda2 /dev/sda ls -- -lDevice proc: Filesystem type procfs - Sector size 512B - Total size 0KiBDevice loop0: No known filesystem detected - Sector size 512B - Total size 8200650752KiB    Partition loop0,gpt12: No known filesystem detected - Partition start at 2901366784KiB - Total size 97656832KiB    Partition loop0,gpt11: No known filesystem detected - Partition start at 2891601920KiB - Total size 9764864KiB    Partition loop0,gpt10: No known filesystem detected - Partition start at 2794433536KiB - Total size 97168384KiB    Partition loop0,gpt9: Filesystem type xfs, UUID b5c911d7-4f55-46da-80fd-d956bad72234 - Partition start at 2793937920KiB - Total size 495616KiB    Partition loop0,gpt8: No known filesystem detected - Partition start at 2269649920KiB - Total size 524288000KiB    Partition loop0,gpt7: No known filesystem detected - Partition start at 1887967232KiB - Total size 381682688KiB    Partition loop0,gpt6: No known filesystem detected - Partition start at 1468532736KiB - Total size 419434496KiB    Partition loop0,gpt5: No known filesystem detected - Partition start at 1049098240KiB - Total size 419434496KiB    Partition loop0,gpt4: No known filesystem detected - Partition start at 524806144KiB - Total size 524292096KiB    Partition loop0,gpt3: No known filesystem detected - Partition start at 514048KiB - Total size 524292096KiB    Partition loop0,gpt2: Filesystem type xfs, UUID 97dfd142-3423-459a-a39e-9a6099b3e5fc - Partition start at 2048KiB - Total size 512000KiB    Partition loop0,gpt1: No known filesystem detected - Partition start at 1024KiB - Total size 1024KiBHelp?
grub2 cannot see filesystem on alternate /boot partition
grub2;dual boot;bootable