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如何擦除/擦除所有 ext4 元数据，而不仅仅是文件系统签名 53 ef？

tag-icon • tag-icon ext4 delete superblock
如何擦除/擦除所有 ext4 元数据，而不仅仅是文件系统签名 53 ef？

我想将存在 ext4 文件系统结构的分区的所有位（超级块、元数据、日志等）清零，而不仅仅是wipefs.

我可以使用实用程序快速将文件内容清零shred，但不能将元数据清零。在支持 的块设备上TRIM/DISCARD，这很容易，因为我可以blkdiscard在整个分区上快速运行。

然而，在不可用的大型旋转 HDD 上TRIM/DISCARD，将所有位设为 0 要么成为一个耗时的过程，要么意味着销毁/重新生成磁盘加密密钥（在自加密驱动器上），这意味着丢失整个驱动器，而不仅仅是 ext4 分区。

除了阅读mke2fs代码并wipe2fs基于它创建一个想象的工具之外，是否还有另一种方法可以快速擦除所有 ext4 超级块/元数据？

答案1

我几年前写了这篇文章，作为脚本化远程安装的一部分，以删除所有超级块，以便后续 mkfs 不会在无人值守安装过程中询问“您真的想这样做吗...”问题。测试仅限于具有 2 个分区的单个设备。

# Overwrite any existing superblocks for the filesystem on each partition
#
# Zero out the superblock where the filesystems will be. If we don't do this,
# when we reimage a disk mkfs will see the superblocks of the filesystem which
# may have previously been here and and ask for a y/n confirmation before
# proceeding which requires more manual intervention (see disk geometry below)
# This gets a little complicated since the mkfs scatters superblocks across the
# partition to protect against failure so you just can't just zero out the
# beginning of the partition.
# Note that fdisk reports in units of 512 byte blocks (-u) ($FD_BS) but
# the file system may have different blocksize ($FS_BS). When we dd seek to zero
# out the superblock, we need to seek X file system blocks (in FS_BS) from
# the beginning of the partition (in FD_BS) so we use the FS_MULT to help make
# the math more obvious.

overwriteAnySuperblocks() {

fdisk -u -l ${TGTDEV} | grep -v EFI |
        sed -n '/^\//{ s/\*/ /; p}' | # only line that start with /, delete '*'
    while read PART FIRST_BLOCK IGNORE_REST_OF_LINE
    do
        FD_BS=512   # fdisk reports in 512 byte blocks
        echo "Partition $PART starts at $FIRST_BLOCK fdisk blocks" >&2
        # get the file system block size - may be a 4k file system
        FS_BS=$(dumpe2fs "${PART}" 2>/dev/null |
                sed -n '/^Block size/s/^Block size: *\([0-9]*$\)/\1/p')
        echo "File system block size from dumpe2fs - FS_BS=$FS_BS" >&2
        [[ -z "${FS_BS}" ]] && continue # no filesystem on this partition
        # file system block as a multiple of 512 byte blocks
        FS_MULT=$(( FS_BS / FD_BS ))
        echo "File system block size $FS_BS is $FS_MULT x $FD_BS fdisk blocks" >&2
        # zero out the beginning of each partition
        # zero out backup superblocks
        dumpe2fs "${PART}" 2>/dev/null |
            sed -n '/superblock/s/^.*block at \([0-9]*\).*/\1/p' |
            while read SUPERBLOCK
            do
                echo "Zeroing superblock at FS $SUPERBLOCK" >&2
                #echo dd if=/dev/zero of=${TGTDEV} bs=${FD_BS} \
                #    seek=$((${FIRST_BLOCK}+(${SUPERBLOCK}*${FS_MULT}))) \
                #    count=2048
                dd if=/dev/zero of=${TGTDEV} bs=${FD_BS} \
                    seek=$(( FIRST_BLOCK + (SUPERBLOCK*FS_MULT) )) \
                    count=2048
            done
    done

}

答案2

我们过去只是简单地在分区的第一个块上添加零

dd if=/dev/zero bs=512 count=512 of=/dev/your_partition

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