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Documentation: add pointer to name_to_dev_t for root= values

Update kernel-parameters.txt to point users to the authoritative comment
for name_to_dev_t.  In addition, updates other places where some
name_to_dev_t behavior was discussed.  All other references to root=
appear to be for explicit sample usage or just side comments when
discussing other kernel parameters.

Signed-off-by: Will Drewry <>
Cc: Kay Sievers <>
Cc: Randy Dunlap <>
Cc: Namhyung Kim <>
Cc: Trond Myklebust <>
Cc: Jens Axboe <>
Signed-off-by: Andrew Morton <>
Signed-off-by: Linus Torvalds <>
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1 parent 2af1416 commit f2d34fd9435c7e60cb5189d036efe9abfc911862 @redpig redpig committed with torvalds Aug 3, 2011
Showing with 25 additions and 3 deletions.
  1. +10 −3 Documentation/frv/booting.txt
  2. +1 −0 Documentation/kernel-parameters.txt
  3. +14 −0 Documentation/m68k/kernel-options.txt
@@ -106,13 +106,20 @@ separated by spaces:
To use the first on-chip serial port at baud rate 115200, no parity, 8
bits, and no flow control.
- (*) root=/dev/<xxxx>
+ (*) root=<xxxx>
- This specifies the device upon which the root filesystem resides. For
- example:
+ This specifies the device upon which the root filesystem resides. It
+ may be specified by major and minor number, device path, or even
+ partition uuid, if supported. For example:
/dev/nfs NFS root filesystem
/dev/mtdblock3 Fourth RedBoot partition on the System Flash
+ PARTUUID=00112233-4455-6677-8899-AABBCCDDEEFF/PARTNROFF=1
+ first partition after the partition with the given UUID
+ 253:0 Device with major 253 and minor 0
+ Authoritative information can be found in
+ "Documentation/kernel-parameters.txt".
(*) rw
@@ -2245,6 +2245,7 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
ro [KNL] Mount root device read-only on boot
root= [KNL] Root filesystem
+ See name_to_dev_t comment in init/do_mounts.c.
rootdelay= [KNL] Delay (in seconds) to pause before attempting to
mount the root filesystem
@@ -129,6 +129,20 @@ decimal 11 is the major of SCSI CD-ROMs, and the minor 0 stands for
the first of these. You can find out all valid major numbers by
looking into include/linux/major.h.
+In addition to major and minor numbers, if the device containing your
+root partition uses a partition table format with unique partition
+identifiers, then you may use them. For instance,
+"root=PARTUUID=00112233-4455-6677-8899-AABBCCDDEEFF". It is also
+possible to reference another partition on the same device using a
+known partition UUID as the starting point. For example,
+if partition 5 of the device has the UUID of
+00112233-4455-6677-8899-AABBCCDDEEFF then partition 3 may be found as
+ PARTUUID=00112233-4455-6677-8899-AABBCCDDEEFF/PARTNROFF=-2
+Authoritative information can be found in
2.2) ro, rw

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