RAMSIZE linux command manual

RDEV(8)                   Linux Programmer's Manual                   RDEV(8)

       rdev - query/set image root device, RAM disk size, or video mode

       rdev [ -rvh ] [ -o offset ] [ image [ value [ offset ] ] ]
       rdev [ -o offset ] [ image [ root_device [ offset ] ] ]
       ramsize [ -o offset ] [ image [ size [ offset ] ] ]
       vidmode [ -o offset ] [ image [ mode [ offset ] ] ]
       rootflags [ -o offset ] [ image [ flags [ offset ] ] ]

       With no arguments, rdev outputs an /etc/mtab line for the current root
       file system.  With no arguments, ramsize, vidmode, and rootflags print
       usage information.

       In  a  bootable  image for the Linux kernel on i386, there are several
       pairs of bytes which specify the root device, the video mode, and  the
       size of the RAM disk.  These pairs of bytes, by default, begin at off-
       set 504 (decimal) in the kernel image:

               498 Root flags
              (500 and 502 Reserved)
               504 RAM Disk Size
               506 VGA Mode
               508 Root Device
              (510 Boot Signature)

       rdev will change these values.

       Typical values for the image parameter, which is a bootable Linux ker-
       nel image, might be:


       When  using the rdev command, the root_device parameter might be some-
       thing like:


       One may also specify the device by a comma-separated pair  of  decimal
       integers major,minor.

       For  the ramsize command, the size parameter specifies the size of the
       RAM disk in kilobytes.

       For the rootflags command, the flags parameter contains extra informa-
       tion  used  when  mounting  root.   Currently the only effect of these
       flags is to force the kernel to mount the root filesystem in  readonly
       mode if flags is non-zero.

       For the vidmode command, the mode parameter specifies the video mode:

              -3 = Prompt
              -2 = Extended VGA
              -1 = Normal VGA
               0 = as if "0" was pressed at the prompt
               1 = as if "1" was pressed at the prompt
               2 = as if "2" was pressed at the prompt
               n = as if "n" was pressed at the prompt

       If the value is not specified, the image will be examined to determine
       the current settings.

       -r     Causes rdev to act like ramsize.

       -R     Causes rdev to act like rootflags.

       -v     Causes rdev to act like vidmode.

       -h     Provides help.

       The rdev utility, when used other than to find a name for the  current
       root  device, is an ancient hack that works by patching a kernel image
       at a magic offset with magic numbers. It does not  work  on  architec-
       tures  other  than  i386.  Its use is strongly discouraged. Use a boot
       loader like SysLinux or LILO instead.

       At offset 502 there used to be the device number of  the  swap  device
       (in  Linux 0.12), and "rdev -s" or "swapdev" would set this.  However,
       since Linux 0.95 this constant is not used any longer,  and  the  swap
       device is specified using the swapon() system call.

       Originally by Werner Almesberger (almesber@nessie.cs.id.ethz.ch)
       Modified by Peter MacDonald (pmacdona@sanjuan.UVic.CA)
       rootflags support added by Stephen Tweedie (sct@dcs.ed.ac.uk)

Linux 0.99                     20 November 1993                       RDEV(8)