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Ali Razmdideh
Asked: 2019-05-12 07:38:04 +0800 CST

如何在启动时使用服务设置循环设备？

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我正在使用以下命令为 VM 原始映像备份文件设置循环设备：

sudo losetup /dev/loop0 "/home/asus/VirtualBox VMs/Windows RAW/Windows 10.img"

它工作正常。

$ losetup -l
NAME       SIZELIMIT OFFSET AUTOCLEAR RO BACK-FILE                                            DIO LOG-SEC
/dev/loop0         0      0         0  0 /home/asus/VirtualBox VMs/Windows RAW/Windows 10.img   0     512

但我想让这个更改永久化，所以我创建了这个.sevice在启动时运行：

$ cat /etc/systemd/system/loops-setup.service
[Unit]
Description=Setup loop devices
DefaultDependencies=no
Conflicts=umount.target
Before=local-fs.target
After=systemd-udev-settle.service
Required=systemd-udev-settle.service

[Service]
Type=oneshot
ExecStart=/sbin/losetup /dev/loop0 "/home/asus/VirtualBox VMs/Windows RAW/Windows 10.img"
ExecStop=/sbin/losetup -d /dev/loop0
TimeoutSec=60
RemainAfterExit=yes

[Install]
WantedBy=local-fs.target
Also=systemd-udev-settle.service

此服务也可以手动启动：

sudo systemctl start loops-setup

但它在启动时无法启动，并显示此错误：

May 11 19:57:17 ubuntu losetup[308]: losetup: /dev/loop0: failed to set up loop device: No such file or directory

我猜是因为服务的层次结构，我应该改变Before和After选择，但我不知道该怎么做。

提前致谢。

mount services systemd loop-device

1 个回答

  1. Best Answer

    这个问题是由两个原因引起的：

    1.正如@CharlesGreen提到的systemd-udev-settle.service无法激活：

    $ sudo systemctl enable systemd-udev-settle.service
The unit files have no installation config (WantedBy=, RequiredBy=, Also=,
Alias= settings in the [Install] section, and DefaultInstance= for template
units). This means they are not meant to be enabled using systemctl.

Possible reasons for having this kind of units are:
• A unit may be statically enabled by being symlinked from another unit's
  .wants/ or .requires/ directory.
• A unit's purpose may be to act as a helper for some other unit which has
  a requirement dependency on it.
• A unit may be started when needed via activation (socket, path, timer,
  D-Bus, udev, scripted systemctl call, ...).
• In case of template units, the unit is meant to be enabled with some
  instance name specified.

    因此，此服务保持非活动状态：

    $ sudo systemctl status systemd-udev-settle.service
● systemd-udev-settle.service - udev Wait for Complete Device Initialization
   Loaded: loaded (/usr/lib/systemd/system/systemd-udev-settle.service; static; vendor preset: disabled)
   Active: inactive (dead)
     Docs: man:udev(7)
           man:systemd-udevd.service(8)

    2.第二个问题是losetup命令需要访问home分区才能设置Windows 10.img。并且这个分区在启动时没有挂载。

    因此以这种方式更改服务，解决了问题：

    [Unit]
Description=Setup loop devices
DefaultDependencies=no
Conflicts=umount.target
Before=local-fs.target
After=systemd-udevd.service home.mount
Required=systemd-udevd.service

[Service]
Type=oneshot
ExecStart=/sbin/losetup /dev/loop0 "/home/asus/VirtualBox VMs/Windows RAW/Windows 10.img"
ExecStop=/sbin/losetup -d /dev/loop0
TimeoutSec=60
RemainAfterExit=yes

[Install]
WantedBy=local-fs.target
Also=systemd-udevd.service
    • 2

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