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分区设备不存在，但存在于 fdisk -l 上

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分区设备不存在，但存在于 fdisk -l 上

在 Centos 7.7 上我运行命令：

# dd if=/dev/zero of=/root/500MB.img bs=1M count=500
500+0 records in
500+0 records out
524288000 bytes (524 MB) copied, 0.374844 s, 1.4 GB/s
# losetup --all
# losetup /dev/loop0 ./500MB.img
# losetup --all
/dev/loop0: [64768]:33575036 (/root/500MB.img)
# fdisk -l /dev/loop0

Disk /dev/loop0: 524 MB, 524288000 bytes, 1024000 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
# fdisk /dev/loop0
[here set partition]
# fdisk -l /dev/loop0

Disk /dev/loop0: 524 MB, 524288000 bytes, 1024000 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: 0x2b7a6a60

      Device Boot      Start         End      Blocks   Id  System
/dev/loop0p1            2048     1023999      510976   83  Linux
#

但是系统中不存在 /dev/loop0p1：

# pvcreate /dev/loop0p1
  Device /dev/loop0p1 not found.
# ls -ld /dev/loop0p1
ls: cannot access /dev/loop0p1: No such file or directory
# kpartx -l /dev/loop0
loop0p1 : 0 1021952 /dev/loop0 2048
# ls -ld /dev/loop0p1
ls: cannot access /dev/loop0p1: No such file or directory

仅存在循环磁盘设备：

# ls -ld /dev/loop0
brw-rw----. 1 root disk 7, 0 Apr 23 09:31 /dev/loop0

“fdisk -l”上显示的分区在哪里？

更新：由于斯蒂芬·基特的提示已修复。运行所有步骤来修复：

# losetup -d /dev/loop0
# losetup --all
# ls /dev/loop0
/dev/loop0
# fdisk -l /dev/loop0
fdisk: cannot open /dev/loop0: Inappropriate ioctl for device
# fdisk -l ./500MB.img

Disk ./500MB.img: 524 MB, 524288000 bytes, 1024000 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: 0x2b7a6a60

      Device Boot      Start         End      Blocks   Id  System
./500MB.img1            2048     1023999      510976   83  Linux
# losetup -P /dev/loop0 ./500MB.img
# losetup --all
/dev/loop0: [64768]:33575036 (/root/500MB.img)
# ls -ld /dev/loop0*
brw-rw----. 1 root disk   7, 0 Apr 23 10:16 /dev/loop0
brw-rw----. 1 root disk 259, 0 Apr 23 10:16 /dev/loop0p1
#

答案1

你需要告诉内核扫描分区；一种方法是使用losetup，假设您的分区表是在安装设备之前写入的：

  • fdisk在你的图像上运行
  • fdisk -l检查图像上的分区表
  • 将-P选项添加到losetup：losetup -P /dev/loop0 ./500MB.img

最后一步将扫描循环设备中的分区，您将看到/dev/loop0p1.

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