如何制作ubuntu系统（使用Ubuntu制作ext4文件系统）

本文基于Ubuntu 18.04系统，在U盘中制作ext4文件系统。在嵌入式调试中，可以从U盘中挂载文件系统。

# 1、查看U盘设备目录
root@ubuntu:/home/run/code# ls /dev/sd
sda   sda1  sdb   sdb1 (U盘)

# 2、卸载
root@ubuntu:/home/run/code# umount /dev/sdb1

# 3、格式化为ext4文件系统，并添加卷标‘rootfs’
root@ubuntu:/home/run/code# mkfs.ext4 -L rootfs /dev/sdb1
mke2fs 1.44.1 (24-Mar-2018)
Creating filesystem with 7864059 4k blocks and 1966080 inodes
Filesystem UUID: d20aee9e-3ada-4f3e-b806-9bbad7209362
Superblock backups stored on blocks:
        32768, 98304, 163840, 229376, 294912, 819200, 884736, 1605632, 2654208,
        4096000

Allocating group tables: done
Writing inode tables: done
Creating journal (32768 blocks): done
Writing superblocks and filesystem accounting information:

done

root@ubuntu:/home/run/code#

# 4、重新拔插U盘

# 5、拷贝已有文件系统映像ubuntu_rootfs.img
root@ubuntu:/home/run/code# file ubuntu_rootfs.img
ubuntu_rootfs.img: Linux rev 1.0 ext4 filesystem data, UUID=faf10ee9-7e64-4826-98cc-239708736642, volume name "rootfs" (extents) (64bit) (large files) (huge files)

root@ubuntu:/home/run/code# mkdir testimg
root@ubuntu:/home/run/code# mount ubuntu_rootfs.img testimg/
root@ubuntu:/home/run/code# cd testimg/
root@ubuntu:/home/run/code/testimg# ls
bin  boot  dev  etc  home  lib  lost+found  media  opt  proc  root  run  sbin  srv  sys  system  tmp  usr  var  vendor
root@ubuntu:/home/run/code/testimg# mount /dev/sdb1 /tmp/
root@ubuntu:/home/run/code/testimg# cp -rf * /tmp/

# 6、卸载
root@ubuntu:/home/run/code/testimg# umount /tmp

如果原有U盘有多个分区，可以使用fdisk命令删除或创建分区，流程如下：

root@ubuntu:/home/run/code# fdisk /dev/sdc

Welcome to fdisk (util-linux 2.31.1).
Changes will remain in memory only, until you decide to write them.
Be careful before using the write command.


Command (m for help): m  ## 1、帮助

Help:

  Generic
   d   delete a partition
   F   list free unpartitioned space
   l   list known partition types
   n   add a new partition
   p   print the partition table
   t   change a partition type
   v   verify the partition table
   i   print information about a partition

  Misc
   m   print this menu
   x   extra functionality (experts only)

  Script
   I   load disk layout from sfdisk script file
   O   dump disk layout to sfdisk script file

  Save & Exit
   w   write table to disk and exit
   q   quit without saving changes

  Create a new label
   g   create a new empty GPT partition table
   G   create a new empty SGI (IRIX) partition table
   o   create a new empty DOS partition table
   s   create a new empty Sun partition table


Command (m for help): p  ## 2、显示分区
Disk /dev/sdc: 30 GiB, 32212254720 bytes, 62914560 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
Disklabel type: gpt
Disk identifier: 23000000-0000-4C4A-8000-699000005ABB

Device       Start      End  Sectors Size Type
/dev/sdc1    16384    24575     8192   4M unknown
/dev/sdc2    24576    32767     8192   4M unknown
/dev/sdc3    32768    98303    65536  32M unknown
/dev/sdc4    98304   163839    65536  32M unknown
/dev/sdc5   163840   229375    65536  32M unknown
/dev/sdc6   229376  4323327  4093952   2G unknown
/dev/sdc7  4323328 62914495 58591168  28G unknown

Command (m for help): d               ## 3、删除分区7-1
Partition number (1-7, default 7): 7

Partition 7 has been deleted.

Command (m for help): d
Partition number (1-6, default 6):

Partition 6 has been deleted.

Command (m for help): d
Partition number (1-5, default 5):

Partition 5 has been deleted.

Command (m for help): d
Partition number (1-4, default 4):

Partition 4 has been deleted.

Command (m for help): d
Partition number (1-3, default 3):

Partition 3 has been deleted.

Command (m for help): d
Partition number (1,2, default 2): d
Value out of range.
Partition number (1,2, default 2):

Partition 2 has been deleted.

Command (m for help): d
Selected partition 1
Partition 1 has been deleted.

Command (m for help): p                   ## 4、显示分区
Disk /dev/sdc: 30 GiB, 32212254720 bytes, 62914560 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
Disklabel type: gpt
Disk identifier: 23000000-0000-4C4A-8000-699000005ABB

Command (m for help): n                  ## 5、新建分区1
Partition number (1-128, default 1):
First sector (34-62914526, default 2048):
Last sector, +sectors or +size{K,M,G,T,P} (2048-62914526, default 62914526):

Created a new partition 1 of type 'Linux filesystem' and of size 30 GiB.
Partition #1 contains a ext4 signature.

Do you want to remove the signature? [Y]es/[N]o: y

The signature will be removed by a write command.

Command (m for help): p
Disk /dev/sdc: 30 GiB, 32212254720 bytes, 62914560 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
Disklabel type: gpt
Disk identifier: 23000000-0000-4C4A-8000-699000005ABB

Device     Start      End  Sectors Size Type
/dev/sdc1   2048 62914526 62912479  30G Linux filesystem

Filesystem/RAID signature on partition 1 will be wiped.

Command (m for help): w             ## 6、保存退出
The partition table has been altered.
Calling ioctl() to re-read partition table.
Syncing disks.

root@ubuntu:/home/run/code#