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I installed Centos7 on my HDD while I have windows installed on my SSD.
When I tried to set up dual boot. Grub is malfunctioning for some reason.

EVEN ON MY BIOS PAGE, MY WINDOWS INSTALLED SSD IS NOT SHOWN

I'm going to put some outputs from commands...

[root@localhost ~]# lsblk

NAME            MAJ:MIN RM   SIZE RO TYPE MOUNTPOINT

sda               8:0    0 232.9G  0 disk 

├─sda1            8:1    0    16M  0 part 

├─sda2            8:2    0  69.5G  0 part /run/media/root/02B22DB8B22DB159

├─sda3            8:3    0   495M  0 part /run/media/root/6A74253174250185

└─sda4            8:4    0 162.9G  0 part /run/media/root/SSD

sdb               8:16   0   1.8T  0 disk 

├─sdb1            8:17   0   200M  0 part /boot/efi

├─sdb2            8:18   0     1G  0 part /boot

├─sdb3            8:19   0   299G  0 part 

│ ├─centos-root 253:0    0    50G  0 lvm  /

│ ├─centos-swap 253:1    0   7.9G  0 lvm  [SWAP]

│ └─centos-home 253:2    0 241.1G  0 lvm  /home

├─sdb4            8:20   0 635.2G  0 part 

├─sdb5            8:21   0   290G  0 part 

├─sdb6            8:22   0    10G  0 part 

└─sdb7            8:23   0 627.3G  0 part 

And,

[root@localhost ~]# blkid

/dev/sdb1: SEC_TYPE="msdos" UUID="00CB-5870" TYPE="vfat" PARTLABEL="EFI System Partition" PARTUUID="538f6163-4854-46cf-bd70-e3ea7ae00e50" 

/dev/sdb2: UUID="31b39370-d28b-4056-936d-6f86e7bdff12" TYPE="xfs" PARTUUID="c6abf287-12fc-493c-8813-0d9ac1f86087" 

/dev/sdb3: UUID="Q3eIEQ-QsNH-Zot4-GAH0-kKxs-VnQD-glFPGv" TYPE="LVM2_member" PARTUUID="5a473279-5580-4ede-95e8-bf4f4930e1e9" 

/dev/sdb4: LABEL="Important backups" UUID="4266C56266C55777" TYPE="ntfs" PARTLABEL="Basic data partition" PARTUUID="9564925e-0dc1-499c-8ad0-60237843896d" 

/dev/sdb5: LABEL="CentOS" UUID="400E2FE40E2FD1A8" TYPE="ntfs" PARTLABEL="Basic data partition" PARTUUID="2f7116de-0313-4b51-8e94-f199e5c04dc2" 

/dev/sdb6: LABEL="Google" UUID="684A81EC4A81B6FA" TYPE="ntfs" PARTLABEL="Basic data partition" PARTUUID="ddda345b-177a-4783-9701-b0bc84caa267" 

/dev/sdb7: LABEL="Stuff" UUID="FE440BC1440B7C21" TYPE="ntfs" PARTLABEL="Basic data partition" PARTUUID="8d2e7aea-1010-44d5-b246-0b8383ce97c5" 

/dev/sda2: UUID="02B22DB8B22DB159" TYPE="ntfs" PARTLABEL="Basic data partition" PARTUUID="aed8e955-ab05-44aa-832d-b6259f6c7e17" 

/dev/sda3: UUID="6A74253174250185" TYPE="ntfs" PARTUUID="96ab56d1-1ac8-4e39-b82c-03fa4ae14ebd" 

/dev/sda4: LABEL="SSD" UUID="24009939009912C2" TYPE="ntfs" PARTLABEL="Basic data partition" PARTUUID="95d41118-4f6c-46ca-9c20-fd05b28a638e" 

/dev/mapper/centos-root: UUID="cbaa94ca-fb50-4c15-b9b2-6fcaa63f5086" TYPE="xfs" 

/dev/mapper/centos-swap: UUID="6d44bbd7-d20c-45f9-9cac-9186989e8f3a" TYPE="swap" 

/dev/mapper/centos-home: UUID="1c40e7f3-c1be-41e4-a971-b26f5812760c" TYPE="xfs" 

/dev/sda1: PARTLABEL="Microsoft reserved partition" PARTUUID="abf7e6f3-a94a-41e8-bae3-482932bc56fa" 

as you can see, I have the windows partitions mounted

However, when I run os-prober,

[root@localhost ~]# os-prober

[root@localhost ~]# 

It returns nothing...
So I tried manually editing grub like:

[root@localhost etc]# vim grub2-efi.cfg

#

# DO NOT EDIT THIS FILE

#

# It is automatically generated by grub2-mkconfig using templates

# from /etc/grub.d and settings from /etc/default/grub

#



### BEGIN /etc/grub.d/00_header ###

set pager=1



if [ -s $prefix/grubenv ]; then

  load_env

fi

if [ "${next_entry}" ] ; then

   set default="${next_entry}"

   set next_entry=

   save_env next_entry

   set boot_once=true

else

   set default="${saved_entry}"

fi



if [ x"${feature_menuentry_id}" = xy ]; then

  menuentry_id_option="--id"

else

  menuentry_id_option=""

fi



export menuentry_id_option



if [ "${prev_saved_entry}" ]; then

  set saved_entry="${prev_saved_entry}"

  save_env saved_entry

  set prev_saved_entry=

  save_env prev_saved_entry

  set boot_once=true

fi



function savedefault {

  if [ -z "${boot_once}" ]; then

    saved_entry="${chosen}"

    save_env saved_entry

  fi

}



function load_video {

  if [ x$feature_all_video_module = xy ]; then

    insmod all_video

  else

    insmod efi_gop

    insmod efi_uga

    insmod ieee1275_fb

    insmod vbe

    insmod vga

    insmod video_bochs

    insmod video_cirrus

  fi

}



terminal_output console

if [ x$feature_timeout_style = xy ] ; then

  set timeout_style=menu

  set timeout=5

# Fallback normal timeout code in case the timeout_style feature is

# unavailable.

else

  set timeout=5

fi

### END /etc/grub.d/00_header ###



### BEGIN /etc/grub.d/00_tuned ###

set tuned_params=""

set tuned_initrd=""

### END /etc/grub.d/00_tuned ###



### BEGIN /etc/grub.d/01_users ###

if [ -f ${prefix}/user.cfg ]; then

  source ${prefix}/user.cfg

  if [ -n "${GRUB2_PASSWORD}" ]; then

    set superusers="root"

    export superusers

    password_pbkdf2 root ${GRUB2_PASSWORD}

  fi

fi

### END /etc/grub.d/01_users ###



### BEGIN /etc/grub.d/10_linux ###

menuentry 'CentOS Linux (3.10.0-693.el7.x86_64) 7 (Core)' --class centos --class gnu-linux --class gnu --class os --unrestricted $menuentry_id_option 'gnulinux-3.10.0-693.el7.x86_64-advanced-cbaa94ca-fb50-4c15-b9b2-6fcaa63f5086' {

    load_video

    set gfxpayload=keep

    insmod gzio

    insmod part_gpt

    insmod xfs

    set root='hd1,gpt2'

    if [ x$feature_platform_search_hint = xy ]; then

      search --no-floppy --fs-uuid --set=root --hint-bios=hd1,gpt2 --hint-efi=hd1,gpt2 --hint-baremetal=ahci1,gpt2  31b39370-d28b-4056-936d-6f86e7bdff12

    else

      search --no-floppy --fs-uuid --set=root 31b39370-d28b-4056-936d-6f86e7bdff12

    fi

    linuxefi /vmlinuz-3.10.0-693.el7.x86_64 root=/dev/mapper/centos-root ro crashkernel=auto rd.lvm.lv=centos/root rd.lvm.lv=centos/swap rhgb quiet 

    initrdefi /initramfs-3.10.0-693.el7.x86_64.img

}

menuentry 'CentOS Linux (0-rescue-b6e43f208d5e496e9f3478a7c353da78) 7 (Core)' --class centos --class gnu-linux --class gnu --class os --unrestricted $menuentry_id_option 'gnulinux-0-rescue-b6e43f208d5e496e9f3478a7c353da78-advanced-cbaa94ca-fb50-4c15-b9b2-6fcaa63f5086' {

    load_video

    insmod gzio

    insmod part_gpt

    insmod xfs

    set root='hd1,gpt2'

    if [ x$feature_platform_search_hint = xy ]; then

      search --no-floppy --fs-uuid --set=root --hint-bios=hd1,gpt2 --hint-efi=hd1,gpt2 --hint-baremetal=ahci1,gpt2  31b39370-d28b-4056-936d-6f86e7bdff12

    else

      search --no-floppy --fs-uuid --set=root 31b39370-d28b-4056-936d-6f86e7bdff12

    fi

    linuxefi /vmlinuz-0-rescue-b6e43f208d5e496e9f3478a7c353da78 root=/dev/mapper/centos-root ro crashkernel=auto rd.lvm.lv=centos/root rd.lvm.lv=centos/swap rhgb quiet 

    initrdefi /initramfs-0-rescue-b6e43f208d5e496e9f3478a7c353da78.img

}

if [ "x$default" = 'CentOS Linux (3.10.0-693.el7.x86_64) 7 (Core)' ]; then default='Advanced options for CentOS Linux>CentOS Linux (3.10.0-693.el7.x86_64) 7 (Core)'; fi;

### END /etc/grub.d/10_linux ###



### BEGIN /etc/grub.d/20_linux_xen ###

### END /etc/grub.d/20_linux_xen ###



### BEGIN /etc/grub.d/20_ppc_terminfo ###

### END /etc/grub.d/20_ppc_terminfo ###



### BEGIN /etc/grub.d/30_os-prober ###

### END /etc/grub.d/30_os-prober ###



### BEGIN /etc/grub.d/40_custom ###

# This file provides an easy way to add custom menu entries.  Simply type the

# menu entries you want to add after this comment.  Be careful not to change

# the 'exec tail' line above.

menuentry "Windows10" {

    insmod ntfs

    insmod ntldr

    insmod part_msdos

    insmod search_fs_uuid

    search --fs-uuid --no-floppy --set=root 6A74253174250185

    ntldr /bootmgr

}

### END /etc/grub.d/40_custom ###



### BEGIN /etc/grub.d/41_custom ###

if [ -f  ${config_directory}/custom.cfg ]; then

  source ${config_directory}/custom.cfg

elif [ -z "${config_directory}" -a -f  $prefix/custom.cfg ]; then

  source $prefix/custom.cfg;

fi

### END /etc/grub.d/41_custom ###

And When I select Windows10 at the GRUB screen,

It shows

error: file `/EFI/centos/x86_64-efi/ntfs.mod' not found.

error: file `/EFI/centos/x86_64-efi/ntldr.mod' not found.

error: no such device: 6A74253174250185.

error: can't find command `ntldr`



Press any key to continue...

** I have ntfs3g installed.

[root@localhost ~]# rpm -qa | grep ntfs

ntfs-3g-2017.3.23-6.el7.x86_64

** Result of fdisk -l

[root@localhost ~]# fdisk -l



Disk /dev/sda: 250.1 GB, 250059350016 bytes, 488397168 sectors

Units = sectors of 1 * 512 = 512 bytes

Sector size (logical/physical): 512 bytes / 512 bytes

I/O size (minimum/optimal): 512 bytes / 512 bytes

Disk label type: dos

Disk identifier: 0x00000000



   Device Boot      Start         End      Blocks   Id  System

/dev/sda1               1  4294967295  2147483647+  ee  GPT

WARNING: fdisk GPT support is currently new, and therefore in an experimental phase. Use at your own discretion.



Disk /dev/sdb: 2000.4 GB, 2000398934016 bytes, 3907029168 sectors

Units = sectors of 1 * 512 = 512 bytes

Sector size (logical/physical): 512 bytes / 4096 bytes

I/O size (minimum/optimal): 4096 bytes / 4096 bytes

Disk label type: gpt

Disk identifier: 7579DF4B-DDA7-4CEC-89B9-7D196B2E0516





#         Start          End    Size  Type            Name

 1         2048       411647    200M  EFI System      EFI System Partition

 2   3277879296   3279976447      1G  Microsoft basic 

 3   3279976448   3907028991    299G  Linux LVM       

 4      1161216   1333180415  635.2G  Microsoft basic Basic data partition

 5   1333180416   1941350399    290G  Microsoft basic Basic data partition

 6   1941352448   1962323967     10G  Microsoft basic Basic data partition

 7   1962326016   3277879295  627.3G  Microsoft basic Basic data partition



Disk /dev/mapper/centos-root: 53.7 GB, 53687091200 bytes, 104857600 sectors

Units = sectors of 1 * 512 = 512 bytes

Sector size (logical/physical): 512 bytes / 4096 bytes

I/O size (minimum/optimal): 4096 bytes / 4096 bytes





Disk /dev/mapper/centos-swap: 8455 MB, 8455716864 bytes, 16515072 sectors

Units = sectors of 1 * 512 = 512 bytes

Sector size (logical/physical): 512 bytes / 4096 bytes

I/O size (minimum/optimal): 4096 bytes / 4096 bytes





Disk /dev/mapper/centos-home: 258.9 GB, 258901803008 bytes, 505667584 sectors

Units = sectors of 1 * 512 = 512 bytes

Sector size (logical/physical): 512 bytes / 4096 bytes

I/O size (minimum/optimal): 4096 bytes / 4096 bytes

• 
  

  Disable the package/ remove - ntfs-3g-2017.3.23-6.el7.x86_64.

  
  
  

  (NTFS-3g-2017.3.23-6.el7.x86_64 mostly being used for handling windows servers, chances this could be causing the issue)

  
  



• Restart your system < os-prober < update-grub

(use those commands with sudo to get the root access)