linux下的 btrfs¶
btrfs的功能¶
写时复制 copy on right功能使得非常时候做快照。
子卷功能可以更方便的分区。以及添加新设备。
使用¶
btrfs filesystem du -s /path/to/subvolume
BTRFS(8) BTRFS BTRFS(8)
NAME
btrfs - a toolbox to manage btrfs filesystems
SYNOPSIS
btrfs [global options] <group> [<group>...] <command> [options] [<args>]
DESCRIPTION
The btrfs utility is a toolbox for managing btrfs filesystems. There
are command groups to work with subvolumes, devices, for whole filesys‐
tem or other specific actions. See section COMMANDS.
There are also standalone tools for some tasks like btrfs-convert(8) or
btrfstune(8) that were separate historically and/or haven't been merged
to the main utility. See section STANDALONE TOOLS for more details.
For other topics (mount options, etc) please refer to the separate man‐
ual page btrfs(5).
COMMAND SYNTAX
Any command name can be shortened so long as the shortened form is unam‐
biguous, however, it is recommended to use full command names in
scripts. All command groups have their manual page named btrfs-<group>.
For example: it is possible to run btrfs sub snaps instead of btrfs sub‐
volume snapshot. But btrfs file s is not allowed, because file s may be
interpreted both as filesystem show and as filesystem sync.
If the command name is ambiguous, the list of conflicting options is
printed.
Sizes, both upon input and output, can be expressed in either SI or
IEC-I units (see numfmt(1)) with the suffix B appended. All numbers
will be formatted according to the rules of the C locale (ignoring the
shell locale, see locale(7)).
For an overview of a given command use btrfs command --help or btrfs
[command...] help --full to print all available options for all com‐
mands.
There are global options that are passed between btrfs and the group
name and affect behaviour not specific to the command, e.g. verbosity or
the type of the output:
btrfs -q subvolume create ...
btrfs --dry-run subvolume create ...
--format <format>
if supported by the command, print subcommand output in that for‐
mat (text, json)
-v|--verbose
increase verbosity of the subcommand
-q|--quiet
print only errors
--log <level>
set log level (default, info, verbose, debug, quiet)
The remaining options are relevant only for the main tool:
--help print condensed help for all subcommands
--version
print version string
COMMANDS
balance
Balance btrfs filesystem chunks across single or several devices.
See btrfs-balance(8) for details.
check Do off-line check on a btrfs filesystem. See btrfs-check(8) for
details.
device Manage devices managed by btrfs, including add/delete/scan and so
on. See btrfs-device(8) for details.
filesystem
Manage a btrfs filesystem, including label setting/sync and so
on. See btrfs-filesystem(8) for details.
inspect-internal
Debug tools for developers/hackers. See
btrfs-inspect-internal(8) for details.
property
Get/set a property from/to a btrfs object. See btrfs-property(8)
for details.
qgroup Manage quota group(qgroup) for btrfs filesystem. See
btrfs-qgroup(8) for details.
quota Manage quota on btrfs filesystem like enabling/rescan and etc.
See btrfs-quota(8) and btrfs-qgroup(8) for details.
receive
Receive subvolume data from stdin/file for restore and etc. See
btrfs-receive(8) for details.
replace
Replace btrfs devices. See btrfs-replace(8) for details.
rescue Try to rescue damaged btrfs filesystem. See btrfs-rescue(8) for
details.
restore
Try to restore files from a damaged btrfs filesystem. See
btrfs-restore(8) for details.
scrub Scrub a btrfs filesystem. See btrfs-scrub(8) for details.
send Send subvolume data to stdout/file for backup and etc. See
btrfs-send(8) for details.
subvolume
Create/delete/list/manage btrfs subvolume. See
btrfs-subvolume(8) for details.
STANDALONE TOOLS
New functionality could be provided using a standalone tool. If the
functionality proves to be useful, then the standalone tool is declared
obsolete and its functionality is copied to the main tool. Obsolete
tools are removed after a long (years) depreciation period.
Tools that are still in active use without an equivalent in btrfs:
btrfs-convert
in-place conversion from ext2/3/4 filesystems to btrfs
btrfstune
tweak some filesystem properties on a unmounted filesystem
btrfs-select-super
rescue tool to overwrite primary superblock from a spare copy
btrfs-find-root
rescue helper to find tree roots in a filesystem
For space-constrained environments, it's possible to build a single bi‐
nary with functionality of several standalone tools. This is following
the concept of busybox where the file name selects the functionality.
This works for symlinks or hardlinks. The full list can be obtained by
btrfs help --box.
EXIT STATUS
btrfs returns a zero exit status if it succeeds. Non zero is returned in
case of failure.
AVAILABILITY
btrfs is part of btrfs-progs. Please refer to the documentation at ‐
https://btrfs.readthedocs.io.
SEE ALSO
btrfs(5), btrfs-balance(8), btrfs-check(8), btrfs-convert(8),
btrfs-device(8), btrfs-filesystem(8), btrfs-inspect-internal(8),
btrfs-property(8), btrfs-qgroup(8), btrfs-quota(8), btrfs-receive(8),
btrfs-replace(8), btrfs-rescue(8), btrfs-restore(8), btrfs-scrub(8),
btrfs-send(8), btrfs-subvolume(8), btrfstune(8), mkfs.btrfs(8)
6.14 Mar 27, 2025 BTRFS(8)
快照¶
用timeshift和snapper做快照。子卷布局
ID 257 gen 96108 top level 5 path @home
ID 318 gen 105959 top level 257 path @home/username
ID 268 gen 96108 top level 318 path @home/username/.snapshots
ID 269 gen 96108 top level 268 path @home/username/.snapshots/1/snapshot
ID 258 gen 105883 top level 5 path @root
ID 259 gen 105850 top level 5 path @cache
ID 260 gen 105959 top level 5 path @log
ID 261 gen 105942 top level 5 path @tmp
ID 262 gen 98722 top level 5 path @opt
ID 273 gen 96108 top level 262 path @opt/.snapshots
ID 274 gen 96108 top level 258 path @root/.snapshots
ID 285 gen 96433 top level 274 path @root/.snapshots/1/snapshot
ID 290 gen 105959 top level 5 path @
ID 519 gen 96445 top level 268 path @home/username/.snapshots/2/snapshot
ID 536 gen 103272 top level 5 path timeshift-btrfs/snapshots/2025-04-21_12-54-20/@
ID 537 gen 104133 top level 5 path timeshift-btrfs/snapshots/2025-04-21_20-12-43/@
即根目录用timeshift备份，并且回滚过一次（从@的ID可以看出来，不是安装时创建的256），而/home/username,/home/root,/home/opt用snapper做了几个快照
timeshift 备份根目录¶
注意btrfs的子卷布局，根目录必须是@，例如
ID 257 gen 96108 top level 5 path @home
ID 258 gen 105883 top level 5 path @root
ID 259 gen 105850 top level 5 path @cache
ID 260 gen 105930 top level 5 path @log
ID 261 gen 105928 top level 5 path @tmp
ID 262 gen 98722 top level 5 path @opt
ID 290 gen 105929 top level 5 path @
snapper 备份子卷¶
参考：
snapper更加灵活。首先创建一个snapper的配置文件
sudo snapper -c [name of config] create-config [path-to-subvol]
例如对根目录的备份配置，snapper默认配置名是root
sudo snapper -c root create-config /
snapper默认会创建子卷/.snapshots，似乎是opensuse风格的，把它调整成一般的布局
sudo umount /.snapshots
sudo rm -r /.snapshots
sudo btrfs subvolume delete /.snapshots
sudo mkdir /.snapshots
sudo mount -o subvol=/ /dev/nvme0n1p1 /mnt
sudo btrfs subvolume create /mnt/@snapshots
可以对其他子卷做同样的操作，比如对/opt (@opt),/root (@root)。
对用户目录，首先有@home子卷挂载/home，然后用
useradd
Usage: useradd [options] LOGIN
useradd -D
useradd -D [options]
Options:
--btrfs-subvolume-home use BTRFS subvolume for home directory
选项创建@home/user_name子卷挂载用户家目录/home/user_name。这样再用上述方法可以对特定用户的家目录做快照。子卷会像
从快照中恢复¶
对snapper创建的/的快照，复杂的手动方法，要从live
USB开始，就是安装arch时的live系统
sudo mount /dev/nvme0n1p6 /mnt
cd /mnt
sudo mv /mnt/@ /mnt/@.broken
sudo btrfs subvolume snapshot /mnt/@snapshots/{number}/snapshot /mnt/@
sudo btrfs subvolume delete /mnt/@.broken
不进入live系统的方法，看上去很危险，最好回滚后立刻重启
sudo mount -o subvol=/ /dev/nvme0n1p1 /mnt
sudo btrfs subvolume snapshot /mnt/@ /mnt/@bad
sudo btrfs subvolume delete /mnt/@
sudo btrfs subvolume snapshot /mnt/@snapshots/要恢复的快照号/snapshot /mnt/@
可以用脚本完成回滚（来自这里）
#!/bin/sh
set -e
if [[ x"$1" == x ]]; then
echo "No snapshot number given." 1>&2
echo "Usage: rollback [snapshot to rollback]" 1>&2
exit 1
fi
root_dev=`findmnt -n -o SOURCE / | sed 's/\[.*\]//g'`
root_subvol=`findmnt -n -o SOURCE / | sed 's/.*\[\(.*\)\].*/\1/'`
echo ">= Rollback to #$1 on device $root_dev"
# create snapshot before
sudo snapper create --read-only --type single -d "Before rollback to #$1" --userdata important=yes
sudo mount -o subvol=/ $root_dev /mnt
# check enviornment
if [[ x"$root_subvol" == x/@ ]]; then
echo "Warning: Not run in a snapshot, a subvolume @old will be created. You should consider remove it after reboot." 1>&2
if [[ -d /mnt/@old ]]; then
echo "Found last @old, remove it."
sudo btrfs subvolume delete /mnt/@old >/dev/null
fi
sudo mv /mnt/@ /mnt/@old
else
sudo btrfs subvolume delete /mnt/@ >/dev/null
fi
sudo btrfs subvolume snapshot /mnt/@snapshots/$1/snapshot /mnt/@ >/dev/null
sudo umount /mnt
其他子卷的snapper快照，直接用
snapper -c [config] rollback [number]
对于timeshift，直接gui操作就行。
回滚后最好立刻重启。