1Boot time creation of mapped devices 2=================================== 3 4It is possible to configure a device mapper device to act as the root 5device for your system in two ways. 6 7The first is to build an initial ramdisk which boots to a minimal 8userspace which configures the device, then pivot_root(8) in to it. 9 10For simple device mapper configurations, it is possible to boot directly 11using the following kernel command line: 12 13dm="<name> <uuid> <ro>,table line 1,...,table line n" 14 15name = the name to associate with the device 16 after boot, udev, if used, will use that name to label 17 the device node. 18uuid = may be 'none' or the UUID desired for the device. 19ro = may be "ro" or "rw". If "ro", the device and device table will be 20 marked read-only. 21 22Each table line may be as normal when using the dmsetup tool except for 23two variations: 241. Any use of commas will be interpreted as a newline 252. Quotation marks cannot be escaped and cannot be used without 26 terminating the dm= argument. 27 28Unless renamed by udev, the device node created will be dm-0 as the 29first minor number for the device-mapper is used during early creation. 30 31Example 32======= 33 34- Booting to a linear array made up of user-mode linux block devices: 35 36 dm="lroot none 0, 0 4096 linear 98:16 0, 4096 4096 linear 98:32 0" \ 37 root=/dev/dm-0 38 39Will boot to a rw dm-linear target of 8192 sectors split across two 40block devices identified by their major:minor numbers. After boot, udev 41will rename this target to /dev/mapper/lroot (depending on the rules). 42No uuid was assigned. 43