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Btrfs/Native System Root Guide
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This exercise is an update to the original example for re-basing a Gentoo installation's root filesystem to use btrfs found here. In this case, the existing system is a mirror set using two 2TB drives at /dev/sda and /dev/sdb. Two fresh 2TB drives have been added at /dev/sdc and /dev/sdd. In the original exercise, the mdadm array was kept to mirror the /boot partitions on the two drives, while the rest of the partitions were converted to btrfs subvolumes.
This second exercise explores the use of GRUB2 to fully convert the mirror set to use the multi-volume functionality of btrfs, implementing /boot as a mirrored btrfs filesystem and forgoing the need to use an initramfs file on /boot to provide early userspace mounting of the root subvolume. We also will be using the gptfdisk ebuild tools to make a GPT based partition table on the new mirror set in place of a legacy MBR table.
One of the lessons learned here is that GRUB2 (2.00_p5107-r2 here) and the current kernel (3.10.25 here) are not quite up to the job of directly booting a filesystem in a btrfs subvolume, at least, not one in a multi-disc set. However it is able to find a simple filesystem on the default volume of a multi-disc set.
Partitioning
Emerge gptfdisk if you don't already have it. It provides the gdisk, sgdisk, and cgdisk utilities for manipulating GPT partitions. These correspond to the legacy fdisk, sfdisk, and cfdisk utilities for MBR tables.
We followed the write up on GRUB2 here to put together the following GPT scheme that GRUB2 can use and got it working after a false start or two.
root #cgdisk cgdisk 0.8.6
Disk Drive: /dev/sdc
Size: 3907029168, 1.8 TiB
Part. # Size Partition Type Partition Name
----------------------------------------------------------------
1.8 TiB free space
[ Align ] [ Backup ] [ Help ] [ Load ] [ New ] [ Quit ] [ Verify ] [ Write ]
(Choosing new)
First sector (40-3907029134, default = 40): 2048
Size in sectors or {KMGTP} (default = 3907027087): 6144
Hex code or GUID (L to show codes, Enter = 8300): EF02
Enter new partition name, or <Enter> to use the current name:
grub2biosboot
(resulting display)
cgdisk 0.8.6
Disk Drive: /dev/sdc
Size: 3907029168, 1.8 TiB
Part. # Size Partition Type Partition Name
----------------------------------------------------------------
1007.0 KiB free space
1 3.0 MiB BIOS boot partition grub2biosboot
1.8 TiB free space
[ Align ] [ Backup ] [ Help ] [ Load ] [ New ] [ Quit ] [ Verify ] [ Write ]
(arrowing to highlight the 1.8TiB freespace entry and choosing New)
First sector (8192-3907029134, default = 8192):
Size in sectors or {KMGTP} (default = 3907020943): 500M
Hex code or GUID (L to show codes, Enter = 8300):
Enter new partition name, or <Enter> to use the current name:
boot
(resulting display)
cgdisk 0.8.6
Disk Drive: /dev/sdc
Size: 3907029168, 1.8 TiB
Part. # Size Partition Type Partition Name
----------------------------------------------------------------
1007.0 KiB free space
1 3.0 MiB BIOS boot partition grub2biosboot
2 500.0 MiB Linux filesystem boot
1.8 TiB free space
[ Align ] [ Backup ] [ Help ] [ Load ] [ New ] [ Quit ] [ Verify ] [ Write ]
(arrowing to highlight the 1.8TiB freespace entry again and choosing New)
First sector (1032192-3907029134, default = 1032192):
Size in sectors or {KMGTP} (default = 3905996943):
Hex code or GUID (L to show codes, Enter = 8300):
Enter new partition name, or <Enter> to use the current name:
root
(resulting display)
cgdisk 0.8.6
Disk Drive: /dev/sdc
Size: 3907029168, 1.8 TiB
Part. # Size Partition Type Partition Name
----------------------------------------------------------------
1007.0 KiB free space
1 3.0 MiB BIOS boot partition grub2biosboot
2 500.0 MiB Linux filesystem boot
3 1.8 TiB Linux filesystem root
[ Align ] [ Backup ] [ Help ] [ Load ] [ New ] [ Quit ] [ Verify ] [ Write ]
The grub2biosboot partition was what got missed on the first round and thus got added later.
- 1007.0KiB free space - Will eventually get the boot record and leave enough of a gap for GRUB2 to park its BIOS.
- biosboot - The partition type 0xEF02 (BIOS boot partition) must be set in order for GRUB2 to find it and use it. Some web pages suggest using EF00 (EFI System), but this will not work with the current version of GRUB2. The bare minimum for this size is 1mb, but some pages suggest using at least 2 MBs. We err on the side of caution and future bloat.
- boot - GRUB2 will take about 32mb more of /boot than you may be used to so the usual suggestion of 200mb in days past is now more like 300mb - 500mb depending on how many kernels and initramfs filesystems you like to keep around. Set the partition type to the default which is 0x8300 for Linux.
- root - We took the default for size to allocate the rest of the drive to the root partition. Once again the type is set to 0x8300.
The resulting table looks like the following in gdisk:
root #gdisk /dev/sdcGPT fdisk (gdisk) version 0.8.6 Partition table scan: MBR: protective BSD: not present APM: not present GPT: present Found valid GPT with protective MBR; using GPT. Command (? for help): p Disk /dev/sdc: 3907029168 sectors, 1.8 TiB Logical sector size: 512 bytes Disk identifier (GUID): A5C43D4A-ED5A-4173-BDC0-5D632C0BAEEF Partition table holds up to 128 entries First usable sector is 34, last usable sector is 3907029134 Partitions will be aligned on 2048-sector boundaries Total free space is 2014 sectors (1007.0 KiB) Number Start (sector) End (sector) Size Code Name 1 2048 8191 3.0 MiB EF02 grub2biosboot 2 8192 1032191 500.0 MiB 8300 boot 3 1032192 3907029134 1.8 TiB 8300 root Command (? for help):
Note
You may not see the "MBR: protective" indication in the output unless an MBR has been written to the drive at least once.
You may not see the "MBR: protective" indication in the output unless an MBR has been written to the drive at least once.
Repeat the same partitioning on /dev/sdd. Similar to sfdisk, the sgdisk utility has the ability to dump the GPT table to a file and then reload that. However the output is binary, so we just went ahead and used cgdisk to create the same layout on /dev/sdd.
Filesystem creation
Since this is a two disk simple mirror, we specify raid1 for both metadata and data when making the two filesystems. If you have more than two drives, the current stable versions of kernel (3.10.25) and btrfs-progs (3.12-r1) now also make raid5 and raid6 available for options alongside raid1 and raid10.
root #mkfs -t btrfs -L BOOT -m raid1 -d raid1 /dev/sdc2 /dev/sdd2SMALL VOLUME: forcing mixed metadata/data groups
WARNING! - Btrfs v3.12 IS EXPERIMENTAL
WARNING! - see http://btrfs.wiki.kernel.org before using
Turning ON incompat feature 'mixed-bg': mixed data and metadata block groups
Turning ON incompat feature 'extref': increased hardlink limit per file to 65536
Created a data/metadata chunk of size 8388608
adding device /dev/sdd2 id 2
fs created label BTBOOT on /dev/sdc2
nodesize 4096 leafsize 4096 sectorsize 4096 size 1000.00MiB
Btrfs v3.12
root #mkfs -t btrfs -L BTROOT -m raid1 -d raid1 /dev/sdc3 /dev/sdd3
WARNING! - Btrfs v3.12 IS EXPERIMENTAL
WARNING! - see http://btrfs.wiki.kernel.org before using
Turning ON incompat feature 'extref': increased hardlink limit per file to 65536
adding device /dev/sdd3 id 2
fs created label BTROOT on /dev/sdc3
nodesize 16384 leafsize 16384 sectorsize 4096 size 3.64TiB
Root Volume
We mount the default volume for the root partition on /mnt/newmirror but will be putting the actual contents into subvolumes with different btrfs features enabled or disabled.
root #mkdir /mnt/newmirrorroot #mount -t btrfs -o defaults,noatime,compress=lzo,autodefrag /dev/sdc3 /mnt/newmirror
The new root filesystem will go onto a subvolume (activeroot) which is created on the mirror and then mounted to /mnt/newroot
root #mkdir /mnt/newroot
root #btrfs subvol create /mnt/newmirror/activeroot
root #mount -t btrfs -o defaults,noatime,compress=lzo,autodefrag,subvol=activeroot /dev/sdc3 /mnt/newroot
We mount the existing root filesystem to /mnt/rawroot and use tar to transfer things over while avoiding the dynamic stuff.
root #mkdir /mnt/rawroot
root #mount --bind / /mnt/rawroot
root #cd /mnt/rawroot
root #tar cvpf - . | (cd /mnt/newroot; tar xpf -)40 or so gb worth of stuff in the output log goes by
Boot volume
At this point /mnt/newroot/boot and the mountpoints for the other subvolumes we will be creating are already in place from the tar. We keep the mount options simple for /mnt/newroot/boot.
root #mount -t btrfs -o defaults,noatime /dev/sdc1 /mnt/newroot/boot
root #cd /boot
root #tar cvpf - . | (cd /mnt/newroot/boot; tar xpf -)short and sweet output log goes by
Other volumes
/home is an obvious candidate for a subvolume, but they are easy to create and manage so you will probably have others. In our example we have the following:
- /home
- /distfiles - It doesn't do any good to enable compression strategies for a directory which just has compressed tarballs for the most part.
- /vm - Keeping your virtual machine store in a separate volume eases snapshotting and migrations. We will enable compression here. At various points in btrfs history the use of autodefrag had impacts and issues on VM performance.
- /vmcrypt - If the VM uses drive encryption, the whole compression strategy gets blown out of the water.
root #btrfs subvol create /mnt/newmirror/homeroot #mount -t btrfs -o defaults,noatime,compress=lzo,autodefrag,subvol=home /dev/sdc3 /mnt/newroot/homeroot #btrfs subvol create /mnt/newmirror/distfilesroot #mount -t btrfs -o defaults,noatime,autodefrag,subvol=distfiles /dev/sdc3 /mnt/newroot/distfilesroot #btrfs subvol create /mnt/newmirror/vmroot #mount -t btrfs -o defaults,noatime,compress=lzo,autodefrag,subvol=vm /dev/sdc3 /mnt/newroot/vmroot #btrfs subvol create /mnt/newmirror/vmcryptroot #mount -t btrfs -o defaults,noatime,autodefrag,subvol=vmcrypt /dev/sdc3 /mnt/newroot/vmcryptThis process takes place overnight and a good bit of the next day, so we will gloss over it
Chrooting into /mnt/newroot
We will chroot into the new root filesystem for the next set of steps:
- Edit the fstab
- Update the kernel to use an embedded initram filesystem
- Install grub2 in place of grub0.97
Pre-chroot preparation
We do the usual prelims to allow GRUB to find things when installing.
root #mount --bind /dev /mnt/newroot/devroot #mount -t proc none /mnt/newroot/proc
Edit your mtab to look something like this:
FILE
/mnt/newroot/etc/mtabthe new root and boot as they will look to grub/dev/sdc3 / btrfs rw,noatime,compress=lzo,autodefrag,subvol=activeroot 0 0 /dev/sdc2 /boot btrfs rw,noatime 0 0
root #chroot /mnt/newroot /bin/bashroot #env-update>>> Regenerating /etc/ld.so.cache...
root #source /etc/profileUpdating fstab
We edit our new fstab to make it look something like this:
FILE
/etc/fstabedited in the chroot so is actually /mnt/newroot/etc/fstab# /etc/fstab: static file system information. # # noatime turns off atimes for increased performance (atimes normally aren't # needed; notail increases performance of ReiserFS (at the expense of storage # efficiency). It's safe to drop the noatime options if you want and to # switch between notail / tail freely. # # The root filesystem should have a pass number of either 0 or 1. # All other filesystems should have a pass number of 0 or greater than 1. # # See the manpage fstab(5) for more information. # # <fs> <mountpoint> <type> <opts> <dump/pass> /dev/sr0 /mnt/cdrom auto ro,noauto,users 0 0 # glibc 2.2 and above expects tmpfs to be mounted at /dev/shm for # POSIX shared memory (shm_open, shm_unlink). # (tmpfs is a dynamically expandable/shrinkable ramdisk, and will # use almost no memory if not populated with files) shm /dev/shm tmpfs nodev,nosuid,noexec 0 0 >>> Regenerating /etc/ld.so.cache... LABEL=BTROOT /mnt/btrfsmirror btrfs defaults,noatime,compress=lzo,autodefrag 0 0 LABEL=BTROOT / btrfs defaults,noatime,compress=lzo,autodefrag,subvol=activeroot 0 0 LABEL=BTROOT /home btrfs defaults,noatime,compress=lzo,autodefrag,subvol=home 0 0 LABEL=BTROOT /distfiles btrfs defaults,noatime,autodefrag,subvol=distfiles 0 0 LABEL=BTROOT /vm btrfs defaults,noatime,compress=lzo,autodefrag,subvol=vm 0 0 LABEL=BTROOT /vmcrypt btrfs defaults,noatime,autodefrag,subvol=vmcrypt 0 0 LABEL=BTBOOT /boot btrfs defaults,noatime 0 0
Embedding an initram filesystem
As we noted in the introduction, the current kernel and GRUB2 combination appear to work fine at least when searching for and mounting the simple /boot mirror btrfs filesystem in the default volume. However we put our new root in a subvolume in order to take advantage of snapshotting and rollback of root as necessary. To do that, we will follow the guide for Early Userspace Mounting again but will also draw upon one of its references in order to have the kernel build process make the archive and then embed it in the resulting bzImage file. This lets us make grub2_mkconfig do all of the heavy lifting without having to do a custom stanza in /etc/grub.d/40_custom.
root #cd /usr/src/linuxroot #chmod +x usr/gen_init_cpio scripts/gen_initramfs_list.shRun menuconfig to use devtmpfs and to specify an initramfs_list that will be used to put an initramfs into the bzImage:
KERNEL
General setup ---> [*] Initial RAM filesystem and RAM disk (initramfs/initrd) support (/usr/src/linux/initramfs/initramfs_list) Initramfs source file(s) Device Drivers ---> Generic Driver Options ---> -*- Maintain a devtmpfs filesystem to mount at /dev [*] Automount devtmpfs at /dev, after the kernel mounted the rootfs
root #cd initramfsinitramfs_list
We don't want to bloat the bzImage too much so only add the essential busybox, filesystem tools and the nano editor. Use ldd to figure out any dependencies of additional commands that you might add.
FILE
/usr/src/linux/initramfs/initramfs_listFile and attributes list to be used by kernel when doing the embed# directory structure dir /proc 755 0 0 dir /usr 755 0 0 dir /bin 755 0 0 dir /sys 755 0 0 dir /var 755 0 0 dir /lib64 755 0 0 dir /sbin 755 0 0 dir /mnt 755 0 0 dir /mnt/root 755 0 0 dir /mnt/boot 755 0 0 dir /etc 755 0 0 dir /root 700 0 0 dir /dev 755 0 0 # busybox file /bin/busybox /bin/busybox 755 0 0 # # fsck deps # file /sbin/fsck /sbin/fsck 755 0 0 file /lib64/libmount.so.1 /lib64/libmount.so.1 755 0 0 file /lib64/libblkid.so.1 /lib64/libblkid.so.1 755 0 0 file /lib64/libc.so.6 /lib64/libc.so.6 755 0 0 file /lib64/libuuid.so.1 /lib64/libuuid.so.1 755 0 0 file /lib64/ld-linux-x86-64.so.2 /lib64/ld-linux-x86-64.so.2 755 0 0 # # fsck.ext3 and added deps # file /sbin/fsck.ext3 /sbin/fsck.ext3 755 0 0 file /lib64/libext2fs.so.2 /lib64/libext2fs.so.2 755 0 0 file /lib64/libcom_err.so.2 /lib64/libcom_err.so.2 755 0 0 file /lib64/libe2p.so.2 /lib64/libe2p.so.2 755 0 0 file /lib64/libpthread.so.0 /lib64/libpthread.so.0 755 0 0 # # btrfs utils and added deps # file /sbin/btrfs /sbin/btrfs 755 0 0 file /sbin/btrfs-convert /sbin/btrfs-convert 755 0 0 file /sbin/btrfs-debug-tree /sbin/btrfs-debug-tree 755 0 0 file /sbin/btrfs-find-root /sbin/btrfs-find-root 755 0 0 file /sbin/btrfs-image /sbin/btrfs-image 755 0 0 file /sbin/btrfs-map-logical /sbin/btrfs-map-logical 755 0 0 file /sbin/btrfs-show-super /sbin/btrfs-show-super 755 0 0 file /sbin/btrfs-zero-log /sbin/btrfs-zero-log 755 0 0 file /sbin/btrfsck /sbin/btrfsck 755 0 0 file /sbin/btrfstune /sbin/btrfstune 755 0 0 file /sbin/mkfs.btrfs /sbin/mkfs.btrfs 755 0 0 file /lib64/libz.so.1 /lib64/libz.so.1 755 0 0 file /lib64/liblzo2.so.2 /usr/lib64/liblzo2.so.2 755 0 0 # # Nano editor and added deps # file /sbin/nano /usr/bin/nano 755 0 0 file /lib64/libncursesw.so.5 /lib64/libncursesw.so.5 755 0 0 file /lib64/libdl.so.2 /lib64/libdl.so.2 755 0 0 # # mknod and added deps # file /sbin/mknod /bin/mknod 755 0 0 # # more viewer # file /sbin/more /bin/more 755 0 0 # # init script # file /init /usr/src/linux/initramfs/init 755 0 0 # # fstab # file /etc/fstab /usr/src/linux/initramfs/fstab 644 0 0
init script alternatives
We started with the init script from the previous exercise but have modified it to create two alternatives. The first should parse the /proc/cmdline to pull the information needed to mount root. It thus doesn't need to use the embedded fstab, but you can place a copy of your normal one in the initramfs directory in case you are dumped to the rescue shell.
The second is a basic mount script that uses an embedded fstab to explicitly spell out the mount entries for root and boot. We resorted to using this when we ran into problems with the init stage and then found that grub2 was not letting busybox open the console device.
/proc/cmdline parsing init script
This has not yet been shown to work during an actual boot, but the logic was tested against busybox on a running system.
FILE
/usr/src/linux/initramfs/init#!/bin/busybox sh rescue_shell() { echo "$@" echo "Something went wrong. Dropping you to a shell." busybox --install -s exec /bin/sh } get_opt() { echo "$@" | cut -d "=" -f 2 } mount_root() { ro="" root="" rootflags="" rootfstype="btrfs" # # This scan is probably not necessary, especially if the grub2 stanzas have put # enough info in /proc/cmdline to find root # echo "Scanning for btrfs filesystems..." /sbin/btrfs device scan /sbin/btrfs fi show for i in $(cat /proc/cmdline); do case $i in root\=*) root=${i:5} ;; ro) ro="ro" ;; rootflags\=*) rootflags=${i:10} ;; rootfstype\=*) rootfstype=$(get_opt $i) ;; esac done case $root in UUID\=*) root="-U ${root:5}" ;; LABEL\=*) root="-L ${root:6}" ;; esac if [[ ${ro} == "ro" ]] ; then if [[ ${rootflags} != "" ]] ; then rootflags="ro,${rootflags}" else rootflags="ro" fi fi echo "mounting /mnt/root" mount -t ${rootfstype} -o ${rootflags} ${root} /mnt/root } # # temporarily mount proc and sys # mount -t proc none /proc mount -t sysfs none /sys mount -t devtmpfs none /dev # # disable kernel messages from popping onto the screen # echo 0 > /proc/sys/kernel/printk # # clear the screen # clear # # mount rootfs on /mnt/root # mount_root || rescue_shell "Error mounting root with /proc/cmdline=$(cat /proc/cmdline)" # # If you are curious about the environment in effect at root, uncomment out these. # The rootfs must not be mounted readonly though. # #cat /proc/mounts >/mnt/root/root/mounts.txt #ls -l / >/mnt/root/root/lsroot.txt #ls -l /dev >/mnt/root/root/lsdev.txt #env >/mnt/root/root/env.txt echo "All done. Switching to real root." # # clean up. The init process will remount proc sys and dev later # umount /proc umount /sys umount /dev # # switch to the real root and execute init # exec switch_root /mnt/root /sbin/init
Basic mount init script
This basic fstab based mount version and the accompanying fstab appears to work:
FILE
/usr/src/linux/initramfs/init#!/bin/busybox sh rescue_shell() { echo "$@" echo "Something went wrong. Dropping you to a shell." busybox --install -s exec /bin/sh } mount_root() { echo "scanning for btrfs filesystems.... will take about 5-10 seconds" # # earlier versions of btrfs required devices on scan. As of around 0.19.11 or so # this now is a syntax error. Also specifying the device= options in the fstab for # the root subvolume probably make this unnecessary now # # /sbin/btrfs device scan /dev/sda /dev/sdb /sbin/btrfs device scan echo "mounting /mnt/root" mount /mnt/root } # temporarily mount proc and sys mount -t proc none /proc mount -t sysfs none /sys mount -t devtmpfs none /dev # disable kernel messages from popping onto the screen echo 0 > /proc/sys/kernel/printk # clear the screen clear # mounting rootfs on /mnt/root mount_root || rescue_shell "Error with uuidlabel_root" cat /proc/mounts >/mnt/root/root/mounts.txt ls -l / >/mnt/root/root/lsroot.txt ls -l /dev >/mnt/root/root/lsdev.txt env >/mnt/root/root/env.txt echo "All done. Switching to real root." # clean up. The init process will remount proc sys and dev later umount /proc umount /sys umount /dev # switch to the real root and execute init exec switch_root /mnt/root /sbin/init
FILE
/usr/src/linux/initramfs/fstabvery specific fstab/dev/sda3 /mnt/root btrfs device=/dev/sda3,device=/dev/sdb3,defaults,noatime,compress=lzo,autodefrag,subvol=activeroot 0 0 /dev/sda2 /mnt/boot btrfs device=/dev/sda2,device=/dev/sdb2,defaults,noatime 0 0
Debug boot environment files
It was interesting to see what the environment inside the kernel looks like.
FILE
/root/mounts.txtResult of "cat /proc/mounts"rootfs / rootfs rw 0 0 none /proc proc rw,relatime 0 0 none /sys sysfs rw,relatime 0 0 none /dev devtmpfs rw,relatime,size=12328636k,nr_inodes=3082159,mode=755 0 0 /dev/sda3 /mnt/root btrfs rw,noatime,compress=lzo,space_cache,autodefrag 0 0
FILE
/root/lsroot.txtResult of "ls -l /" shows our initramfs as roottotal 24 drwxr-xr-x 2 0 0 0 Feb 20 22:21 bin drwxr-xr-x 8 0 0 3480 Mar 5 21:48 dev -rwxr-xr-x 1 0 0 191 Feb 20 20:36 doit drwxr-xr-x 2 0 0 0 Mar 5 21:48 etc -rwxr-xr-x 1 0 0 1286 Feb 20 22:21 init drwxr-xr-x 2 0 0 0 Feb 20 22:21 lib64 -rwxr-xr-x 1 0 0 14480 Jan 23 23:17 libdl.so.2 drwxr-xr-x 4 0 0 0 Feb 20 22:21 mnt dr-xr-xr-x 168 0 0 0 Mar 5 21:48 proc drwx------ 2 0 0 0 Feb 20 22:21 root drwxr-xr-x 2 0 0 0 Feb 20 22:21 sbin dr-xr-xr-x 12 0 0 0 Mar 5 21:48 sys drwxr-xr-x 2 0 0 0 Feb 20 22:21 usr drwxr-xr-x 2 0 0 0 Feb 20 22:21 var
FILE
/root/lsdev.txtwhat devtmpfs gives us for device tree"total 0 crw------- 1 0 0 14, 4 Mar 5 21:48 audio crw------- 1 0 0 10, 235 Mar 5 21:48 autofs drwxr-xr-x 2 0 0 160 Mar 5 21:48 bsg crw------- 1 0 0 10, 234 Mar 5 21:48 btrfs-control drwxr-xr-x 3 0 0 60 Mar 5 21:48 bus crw------- 1 0 0 5, 1 Mar 5 21:48 console drwxr-xr-x 14 0 0 300 Mar 5 21:48 cpu crw------- 1 0 0 10, 57 Mar 5 21:48 cpu_dma_latency crw------- 1 0 0 10, 62 Mar 5 21:48 dlm-control crw------- 1 0 0 10, 61 Mar 5 21:48 dlm-monitor crw------- 1 0 0 10, 60 Mar 5 21:48 dlm_plock crw------- 1 0 0 14, 3 Mar 5 21:48 dsp crw-rw-rw- 1 0 0 1, 7 Mar 5 21:48 full crw------- 1 0 0 247, 0 Mar 5 21:48 hidraw0 crw------- 1 0 0 247, 1 Mar 5 21:48 hidraw1 crw------- 1 0 0 10, 228 Mar 5 21:48 hpet drwxr-xr-x 2 0 0 280 Mar 5 21:48 input crw------- 1 0 0 1, 2 Mar 5 21:48 kmem crw-r--r-- 1 0 0 1, 11 Mar 5 21:48 kmsg crw------- 1 0 0 10, 237 Mar 5 21:48 loop-control brw------- 1 0 0 7, 0 Mar 5 21:48 loop0 brw------- 1 0 0 7, 1 Mar 5 21:48 loop1 brw------- 1 0 0 7, 2 Mar 5 21:48 loop2 brw------- 1 0 0 7, 3 Mar 5 21:48 loop3 brw------- 1 0 0 7, 4 Mar 5 21:48 loop4 brw------- 1 0 0 7, 5 Mar 5 21:48 loop5 brw------- 1 0 0 7, 6 Mar 5 21:48 loop6 brw------- 1 0 0 7, 7 Mar 5 21:48 loop7 drwxr-xr-x 2 0 0 60 Mar 5 21:48 mapper crw------- 1 0 0 10, 227 Mar 5 21:48 mcelog crw------- 1 0 0 10, 58 Mar 5 21:48 megadev0 crw------- 1 0 0 1, 1 Mar 5 21:48 mem crw------- 1 0 0 14, 0 Mar 5 21:48 mixer crw------- 1 0 0 10, 221 Mar 5 21:48 mpt2ctl crw------- 1 0 0 10, 222 Mar 5 21:48 mpt3ctl crw------- 1 0 0 10, 220 Mar 5 21:48 mptctl crw------- 1 0 0 10, 56 Mar 5 21:48 network_latency crw------- 1 0 0 10, 55 Mar 5 21:48 network_throughput crw-rw-rw- 1 0 0 1, 3 Mar 5 21:48 null crw------- 1 0 0 10, 144 Mar 5 21:48 nvram crw------- 1 0 0 1, 12 Mar 5 21:48 oldmem crw------- 1 0 0 1, 4 Mar 5 21:48 port crw-rw-rw- 1 0 0 5, 2 Mar 5 21:48 ptmx brw------- 1 0 0 1, 0 Mar 5 21:48 ram0 brw------- 1 0 0 1, 1 Mar 5 21:48 ram1 brw------- 1 0 0 1, 10 Mar 5 21:48 ram10 brw------- 1 0 0 1, 11 Mar 5 21:48 ram11 brw------- 1 0 0 1, 12 Mar 5 21:48 ram12 brw------- 1 0 0 1, 13 Mar 5 21:48 ram13 brw------- 1 0 0 1, 14 Mar 5 21:48 ram14 brw------- 1 0 0 1, 15 Mar 5 21:48 ram15 brw------- 1 0 0 1, 2 Mar 5 21:48 ram2 brw------- 1 0 0 1, 3 Mar 5 21:48 ram3 brw------- 1 0 0 1, 4 Mar 5 21:48 ram4 brw------- 1 0 0 1, 5 Mar 5 21:48 ram5 brw------- 1 0 0 1, 6 Mar 5 21:48 ram6 brw------- 1 0 0 1, 7 Mar 5 21:48 ram7 brw------- 1 0 0 1, 8 Mar 5 21:48 ram8 brw------- 1 0 0 1, 9 Mar 5 21:48 ram9 crw-rw-rw- 1 0 0 1, 8 Mar 5 21:48 random crw------- 1 0 0 254, 0 Mar 5 21:48 rtc0 brw------- 1 0 0 8, 0 Mar 5 21:48 sda brw------- 1 0 0 8, 1 Mar 5 21:48 sda1 brw------- 1 0 0 8, 2 Mar 5 21:48 sda2 brw------- 1 0 0 8, 3 Mar 5 21:48 sda3 brw------- 1 0 0 8, 16 Mar 5 21:48 sdb brw------- 1 0 0 8, 17 Mar 5 21:48 sdb1 brw------- 1 0 0 8, 18 Mar 5 21:48 sdb2 brw------- 1 0 0 8, 19 Mar 5 21:48 sdb3 brw------- 1 0 0 8, 32 Mar 5 21:48 sdc brw------- 1 0 0 8, 33 Mar 5 21:48 sdc1 brw------- 1 0 0 8, 34 Mar 5 21:48 sdc2 brw------- 1 0 0 8, 35 Mar 5 21:48 sdc3 brw------- 1 0 0 8, 48 Mar 5 21:48 sdd brw------- 1 0 0 8, 49 Mar 5 21:48 sdd1 brw------- 1 0 0 8, 50 Mar 5 21:48 sdd2 brw------- 1 0 0 8, 51 Mar 5 21:48 sdd3 crw------- 1 0 0 14, 1 Mar 5 21:48 sequencer crw------- 1 0 0 14, 8 Mar 5 21:48 sequencer2 crw------- 1 0 0 21, 0 Mar 5 21:48 sg0 crw------- 1 0 0 21, 1 Mar 5 21:48 sg1 crw------- 1 0 0 21, 2 Mar 5 21:48 sg2 crw------- 1 0 0 21, 3 Mar 5 21:48 sg3 crw------- 1 0 0 21, 4 Mar 5 21:48 sg4 drwxr-xr-x 2 0 0 180 Mar 5 21:48 snd brw------- 1 0 0 11, 0 Mar 5 21:48 sr0 crw------- 1 0 0 10, 59 Mar 5 21:48 tgt crw-rw-rw- 1 0 0 5, 0 Mar 5 21:48 tty crw------- 1 0 0 4, 0 Mar 5 21:48 tty0 crw------- 1 0 0 4, 1 Mar 5 21:48 tty1 crw------- 1 0 0 4, 10 Mar 5 21:48 tty10 crw------- 1 0 0 4, 11 Mar 5 21:48 tty11 crw------- 1 0 0 4, 12 Mar 5 21:48 tty12 crw------- 1 0 0 4, 13 Mar 5 21:48 tty13 crw------- 1 0 0 4, 14 Mar 5 21:48 tty14 crw------- 1 0 0 4, 15 Mar 5 21:48 tty15 crw------- 1 0 0 4, 16 Mar 5 21:48 tty16 crw------- 1 0 0 4, 17 Mar 5 21:48 tty17 crw------- 1 0 0 4, 18 Mar 5 21:48 tty18 crw------- 1 0 0 4, 19 Mar 5 21:48 tty19 crw------- 1 0 0 4, 2 Mar 5 21:48 tty2 crw------- 1 0 0 4, 20 Mar 5 21:48 tty20 crw------- 1 0 0 4, 21 Mar 5 21:48 tty21 crw------- 1 0 0 4, 22 Mar 5 21:48 tty22 crw------- 1 0 0 4, 23 Mar 5 21:48 tty23 crw------- 1 0 0 4, 24 Mar 5 21:48 tty24 crw------- 1 0 0 4, 25 Mar 5 21:48 tty25 crw------- 1 0 0 4, 26 Mar 5 21:48 tty26 crw------- 1 0 0 4, 27 Mar 5 21:48 tty27 crw------- 1 0 0 4, 28 Mar 5 21:48 tty28 crw------- 1 0 0 4, 29 Mar 5 21:48 tty29 crw------- 1 0 0 4, 3 Mar 5 21:48 tty3 crw------- 1 0 0 4, 30 Mar 5 21:48 tty30 crw------- 1 0 0 4, 31 Mar 5 21:48 tty31 crw------- 1 0 0 4, 32 Mar 5 21:48 tty32 crw------- 1 0 0 4, 33 Mar 5 21:48 tty33 crw------- 1 0 0 4, 34 Mar 5 21:48 tty34 crw------- 1 0 0 4, 35 Mar 5 21:48 tty35 crw------- 1 0 0 4, 36 Mar 5 21:48 tty36 crw------- 1 0 0 4, 37 Mar 5 21:48 tty37 crw------- 1 0 0 4, 38 Mar 5 21:48 tty38 crw------- 1 0 0 4, 39 Mar 5 21:48 tty39 crw------- 1 0 0 4, 4 Mar 5 21:48 tty4 crw------- 1 0 0 4, 40 Mar 5 21:48 tty40 crw------- 1 0 0 4, 41 Mar 5 21:48 tty41 crw------- 1 0 0 4, 42 Mar 5 21:48 tty42 crw------- 1 0 0 4, 43 Mar 5 21:48 tty43 crw------- 1 0 0 4, 44 Mar 5 21:48 tty44 crw------- 1 0 0 4, 45 Mar 5 21:48 tty45 crw------- 1 0 0 4, 46 Mar 5 21:48 tty46 crw------- 1 0 0 4, 47 Mar 5 21:48 tty47 crw------- 1 0 0 4, 48 Mar 5 21:48 tty48 crw------- 1 0 0 4, 49 Mar 5 21:48 tty49 crw------- 1 0 0 4, 5 Mar 5 21:48 tty5 crw------- 1 0 0 4, 50 Mar 5 21:48 tty50 crw------- 1 0 0 4, 51 Mar 5 21:48 tty51 crw------- 1 0 0 4, 52 Mar 5 21:48 tty52 crw------- 1 0 0 4, 53 Mar 5 21:48 tty53 crw------- 1 0 0 4, 54 Mar 5 21:48 tty54 crw------- 1 0 0 4, 55 Mar 5 21:48 tty55 crw------- 1 0 0 4, 56 Mar 5 21:48 tty56 crw------- 1 0 0 4, 57 Mar 5 21:48 tty57 crw------- 1 0 0 4, 58 Mar 5 21:48 tty58 crw------- 1 0 0 4, 59 Mar 5 21:48 tty59 crw------- 1 0 0 4, 6 Mar 5 21:48 tty6 crw------- 1 0 0 4, 60 Mar 5 21:48 tty60 crw------- 1 0 0 4, 61 Mar 5 21:48 tty61 crw------- 1 0 0 4, 62 Mar 5 21:48 tty62 crw------- 1 0 0 4, 63 Mar 5 21:48 tty63 crw------- 1 0 0 4, 7 Mar 5 21:48 tty7 crw------- 1 0 0 4, 8 Mar 5 21:48 tty8 crw------- 1 0 0 4, 9 Mar 5 21:48 tty9 crw------- 1 0 0 4, 64 Mar 5 21:48 ttyS0 crw------- 1 0 0 4, 65 Mar 5 21:48 ttyS1 crw------- 1 0 0 4, 66 Mar 5 21:48 ttyS2 crw------- 1 0 0 4, 67 Mar 5 21:48 ttyS3 crw-rw-rw- 1 0 0 1, 9 Mar 5 21:48 urandom crw------- 1 0 0 248, 0 Mar 5 21:48 usbmon0 crw------- 1 0 0 248, 1 Mar 5 21:48 usbmon1 crw------- 1 0 0 248, 2 Mar 5 21:48 usbmon2 crw------- 1 0 0 248, 3 Mar 5 21:48 usbmon3 crw------- 1 0 0 248, 4 Mar 5 21:48 usbmon4 crw------- 1 0 0 248, 5 Mar 5 21:48 usbmon5 crw------- 1 0 0 248, 6 Mar 5 21:48 usbmon6 crw------- 1 0 0 248, 7 Mar 5 21:48 usbmon7 crw------- 1 0 0 248, 8 Mar 5 21:48 usbmon8 crw------- 1 0 0 7, 0 Mar 5 21:48 vcs crw------- 1 0 0 7, 1 Mar 5 21:48 vcs1 crw------- 1 0 0 7, 128 Mar 5 21:48 vcsa crw------- 1 0 0 7, 129 Mar 5 21:48 vcsa1 crw------- 1 0 0 10, 63 Mar 5 21:48 vga_arbiter crw-rw-rw- 1 0 0 1, 5 Mar 5 21:48 zero
FILE
/root/env.txtbarebones root environmentHOME=/ TERM=linux BOOT_IMAGE=/kernel-3.10.25-gentoo PWD=/
Rebuilding kernel
root #cd /usr/src/linuxroot #make -j7 bzImage(the scripts and cpio generation are actually done pretty early on if you've already built your kernel at least once) make[1]: Nothing to be done for `all'. CHK include/generated/uapi/linux/version.h HOSTCC scripts/kallsyms HOSTCC scripts/pnmtologo . . HOSTCC usr/gen_init_cpio CHK include/generated/compile.h CC init/main.o AS arch/x86/ia32/ia32entry.o GEN usr/initramfs_data.cpio . . Setup is 17100 bytes (padded to 17408 bytes). System is 11728 kB CRC 8262ef09 Kernel: arch/x86/boot/bzImage is ready (#3)
Our kernel just got about 3-4mb bigger as a result.
root #make -j7 modulesroot #make modules_installroot #cp .config /boot/config-3.10.25-gentooroot #cp System.map /boot/System.map-3.10.25-gentooroot #cd arch/x86_64/bootroot #cp bzImage /boot/kernel-3.10.25-gentooRunning grub2_mkconfig
The mkconfig will have a problem probing the multi-device set as follows:
root #grub2-mkconfig -o /boot/grub/grub.cfgGenerating grub.cfg ... /usr/sbin/grub2-probe: error: cannot find a GRUB drive for /dev/sdc3 /dev/sdd3. Check your device.map. Found linux image: /boot/kernel-3.10.25-gentoo /usr/sbin/grub2-probe: error: cannot find a GRUB drive for /dev/sdc3 /dev/sdd3. Check your device.map. done
This will also cause grub2-install to error out unless we uncomment and specify the GRUB_DEVICE=/dev/sdc3 in /etc/default/grub. When we googled around for this, we found a number of pages such as Fedora bug reports that suggested a patch with bash arrays and jiggered quotes in a GRUB2 script. However it doesn't appear that this patch has gotten far enough upstream or resolved to everyone's liking for Gentoo stable to pick it up yet.
We also uncomment and force GRUB_TERM=console since other pages suggest that there may be issues with GRUB2 using a framebuffer and then running the proprietary nvidia-driver for X11 later on. This may also be true for recent xf86-video-ati driver versions where we are activating a framebuffer before the GPU firmware gets loaded later on from /lib/firmware.
FILE
/etc/default/grubEdited /mnt/newroot/etc/default/grub config file# Copyright 1999-2013 Gentoo Foundation # Distributed under the terms of the GNU General Public License v2 # $Header: /var/cvsroot/gentoo-x86/sys-boot/grub/files/grub.default-2,v 1.4 2013/09/21 18:10:55 floppym Exp $ # # To populate all changes in this file you need to regenerate your # grub configuration file afterwards: # 'grub2-mkconfig -o /boot/grub/grub.cfg' # # See the grub info page for documentation on possible variables and # their associated values. GRUB_DISTRIBUTOR="Gentoo" GRUB_DEFAULT=0 GRUB_HIDDEN_TIMEOUT=0# Copyright 1999-2013 Gentoo Foundation # Distributed under the terms of the GNU General Public License v2 # $Header: /var/cvsroot/gentoo-x86/sys-boot/grub/files/grub.default-2,v 1.4 2013/09/21 18:10:55 floppym Exp $ # # To populate all changes in this file you need to regenerate your # grub configuration file afterwards: # 'grub2-mkconfig -o /boot/grub/grub.cfg' # # See the grub info page for documentation on possible variables and # their associated values. GRUB_DISTRIBUTOR="Gentoo" GRUB_DEFAULT=0 GRUB_HIDDEN_TIMEOUT=0 GRUB_HIDDEN_TIMEOUT_QUIET=true GRUB_TIMEOUT=10 # GRUB_DEVICE forces the initial root device, bypassing the autodetect GRUB_DEVICE=/dev/sdc3 # Append parameters to the linux kernel command line #GRUB_CMDLINE_LINUX="rootfstype=btrfs rootflags=device=/dev/sda2,device=/dev/sdb2,subvol=btroot" # Append parameters to the linux kernel command line for non-recovery entries #GRUB_CMDLINE_LINUX_DEFAULT="" # Uncomment to disable graphical terminal (grub-pc only) GRUB_TERMINAL=console # The resolution used on graphical terminal. # Note that you can use only modes which your graphic card supports via VBE. # You can see them in real GRUB with the command `vbeinfo'. #GRUB_GFXMODE=640x480 # Path to theme spec txt file. # The starfield is by default provided with use truetype. # NOTE: when enabling custom theme, ensure you have required font/etc. #GRUB_THEME="/boot/grub/themes/starfield/theme.txt" # Background image used on graphical terminal. # Can be in various bitmap formats. #GRUB_BACKGROUND="/boot/grub/mybackground.png" # Uncomment if you don't want GRUB to pass "root=UUID=xxx" parameter to kernel #GRUB_DISABLE_LINUX_UUID=true # Uncomment to disable generation of recovery mode menu entries #GRUB_DISABLE_RECOVERY=true GRUB_HIDDEN_TIMEOUT_QUIET=true GRUB_TIMEOUT=10 # GRUB_DEVICE forces the initial root device, bypassing the autodetect GRUB_DEVICE=/dev/sdc3 # Append parameters to the linux kernel command line #GRUB_CMDLINE_LINUX="rootfstype=btrfs rootflags=device=/dev/sda2,device=/dev/sdb2,subvol=btroot" # Append parameters to the linux kernel command line for non-recovery entries #GRUB_CMDLINE_LINUX_DEFAULT="" # Uncomment to disable graphical terminal (grub-pc only) GRUB_TERMINAL=console # The resolution used on graphical terminal. # Note that you can use only modes which your graphic card supports via VBE. # You can see them in real GRUB with the command `vbeinfo'. #GRUB_GFXMODE=640x480 # Path to theme spec txt file. # The starfield is by default provided with use truetype. # NOTE: when enabling custom theme, ensure you have required font/etc. #GRUB_THEME="/boot/grub/themes/starfield/theme.txt" # Background image used on graphical terminal. # Can be in various bitmap formats. #GRUB_BACKGROUND="/boot/grub/mybackground.png" # Uncomment if you don't want GRUB to pass "root=UUID=xxx" parameter to kernel #GRUB_DISABLE_LINUX_UUID=true # Uncomment to disable generation of recovery mode menu entries #GRUB_DISABLE_RECOVERY=true
After the edit the mkconfig now runs without any issues.
root #grub2-mkconfig -o /boot/grub/grub.cfgGenerating grub.cfg ... Found linux image: /boot/kernel-3.10.25-gentoo done
The resulting grub.cfg file will specify the filesystems by uuid since we let that setting default in /etc/default/grub. We can do a sanity check as follows and compare the results.
root #btrfs fi showLabel: BTROOT uuid: 6b9d480d-fd9f-4514-98ad-84d0ace72c90
Total devices 2 FS bytes used 125.48GiB
devid 1 size 1.82TiB used 128.03GiB path /dev/sdc3
devid 2 size 1.82TiB used 128.01GiB path /dev/sdd3
Label: BTBOOT uuid: 3dd38cf0-7591-4d26-9334-84e9f2dafddf
Total devices 2 FS bytes used 27.41MiB
devid 1 size 500.00MiB used 308.00MiB path /dev/sdc2
devid 2 size 500.00MiB used 296.00MiB path /dev/sdd2
Btrfs v3.12
FILE
/boot/grub/grub.cfggenerated /mnt/newroot/boot/grub/grub.cfg file# # 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 ### if [ -s $prefix/grubenv ]; then load_env fi if [ "${next_entry}" ] ; then set default="${next_entry}" set next_entry= save_env next_entry set boot_once=true else set default="0" fi if [ x"${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_input console terminal_output console if sleep --interruptible 0 ; then set timeout=10 fi ### END /etc/grub.d/00_header ### ### BEGIN /etc/grub.d/10_linux ### menuentry 'Gentoo GNU/Linux' --class gentoo --class gnu-linux --class gnu --class os $menuentry_id_option 'gnulinux-simple-6b9d480d-fd9f-4514-98ad-84d0ace72c90' { load_video set gfxpayload=keep insmod gzio insmod part_gpt insmod part_gpt insmod btrfs set root='hd2,gpt2' if [ x$feature_platform_search_hint = xy ]; then search --no-floppy --fs-uuid --set=root 3dd38cf0-7591-4d26-9334-84e9f2dafddf else search --no-floppy --fs-uuid --set=root 3dd38cf0-7591-4d26-9334-84e9f2dafddf fi echo 'Loading Linux 3.10.25-gentoo ...' linux /kernel-3.10.25-gentoo root=UUID=6b9d480d-fd9f-4514-98ad-84d0ace72c90 ro rootflags=subvol=activeroot } submenu 'Advanced options for Gentoo GNU/Linux' $menuentry_id_option 'gnulinux-advanced-6b9d480d-fd9f-4514-98ad-84d0ace72c90' { menuentry 'Gentoo GNU/Linux, with Linux 3.10.25-gentoo' --class gentoo --class gnu-linux --class gnu --class os $menuentry_id_option 'gnulinux-3.10.25-gentoo-advanced-6b9d480d-fd9f-4514-98ad-84d0ace72c90' { load_video set gfxpayload=keep insmod gzio insmod part_gpt insmod part_gpt insmod btrfs set root='hd2,gpt2' if [ x$feature_platform_search_hint = xy ]; then search --no-floppy --fs-uuid --set=root 3dd38cf0-7591-4d26-9334-84e9f2dafddf else search --no-floppy --fs-uuid --set=root 3dd38cf0-7591-4d26-9334-84e9f2dafddf fi echo 'Loading Linux 3.10.25-gentoo ...' linux /kernel-3.10.25-gentoo root=UUID=6b9d480d-fd9f-4514-98ad-84d0ace72c90 ro rootflags=subvol=activeroot } menuentry 'Gentoo GNU/Linux, with Linux 3.10.25-gentoo (recovery mode)' --class gentoo --class gnu-linux --class gnu --class os $menuentry_id_option 'gnulinux-3.10.25-gentoo-recovery-6b9d480d-fd9f-4514-98ad-84d0ace72c90' { load_video set gfxpayload=keep insmod gzio insmod part_gpt insmod part_gpt insmod btrfs set root='hd2,gpt2' if [ x$feature_platform_search_hint = xy ]; then search --no-floppy --fs-uuid --set=root 3dd38cf0-7591-4d26-9334-84e9f2dafddf else search --no-floppy --fs-uuid --set=root 3dd38cf0-7591-4d26-9334-84e9f2dafddf fi echo 'Loading Linux 3.10.25-gentoo ...' linux /kernel-3.10.25-gentoo root=UUID=6b9d480d-fd9f-4514-98ad-84d0ace72c90 ro single rootflags=subvol=activeroot } } ### END /etc/grub.d/10_linux ### ### BEGIN /etc/grub.d/20_linux_xen ### ### END /etc/grub.d/20_linux_xen ### ### 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. ### 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 ###
The set root='hd2,gpt2' statements in the grub.cfg file will be wrong once we remove the original drive set and make the new set /dev/sda and /dev/sdb. However the if-then-else statements right after do a search for the correct UUID for the BTBOOT filesystem and thus will correct the root.
Installing the MBR
We need to run grub2-install on both drives.
root #grub2-install /dev/sdcInstallation finished. No error reported.
root #grub2-install /dev/sddInstallation finished. No error reported.
With the MBR's installed, we also want to go back and re-edit the /etc/default/grub file to reset the GRUB_DEVICE=/dev/sda3 before we forget. It may be a while before we run grub2-mkconfig again to update for a new kernel.