| Boot time creation of mapped devices |
| =================================== |
| |
| It is possible to configure a device mapper device to act as the root |
| device for your system in two ways. |
| |
| The first is to build an initial ramdisk which boots to a minimal |
| userspace which configures the device, then pivot_root(8) in to it. |
| |
| For simple device mapper configurations, it is possible to boot directly |
| using the following kernel command line: |
| |
| dm="<name> <uuid> <ro>,table line 1,...,table line n" |
| |
| name = the name to associate with the device |
| after boot, udev, if used, will use that name to label |
| the device node. |
| uuid = may be 'none' or the UUID desired for the device. |
| ro = may be "ro" or "rw". If "ro", the device and device table will be |
| marked read-only. |
| |
| Each table line may be as normal when using the dmsetup tool except for |
| two variations: |
| 1. Any use of commas will be interpreted as a newline |
| 2. Quotation marks cannot be escaped and cannot be used without |
| terminating the dm= argument. |
| |
| Unless renamed by udev, the device node created will be dm-0 as the |
| first minor number for the device-mapper is used during early creation. |
| |
| Example |
| ======= |
| |
| - Booting to a linear array made up of user-mode linux block devices: |
| |
| dm="lroot none 0, 0 4096 linear 98:16 0, 4096 4096 linear 98:32 0" \ |
| root=/dev/dm-0 |
| |
| Will boot to a rw dm-linear target of 8192 sectors split across two |
| block devices identified by their major:minor numbers. After boot, udev |
| will rename this target to /dev/mapper/lroot (depending on the rules). |
| No uuid was assigned. |