ramdisk(7D) Devices ramdisk(7D)NAME
ramdisk - RAM disk device driver
SYNOPSIS
ramdisk@0:diskname
DESCRIPTION
The ramdisk driver supports numerous ramdisk devices that are created by the system during the boot process (see boot(1M)) or during nor-
mal system operation (see ramdiskadm(1M) for more information).
DEVICE SPECIAL FILES
Each ramdisk can be accessed either as a block device or as a raw device. When accessed as a block device, the normal buffering
mechanism is used when reading from and writing to the device, without regard to physical disk records. Accessing the ramdisk as a raw
device enables direct transmission between the disk and the read or write buffer. A single read or write call usually results in a single
I/O operation, meaning that raw I/O is more efficient when many bytes are transmitted. You can find block files names in /dev/ramdisk. Raw
file names are found in /dev/rramdisk.
There are no alignment or length restrictions on I/O requests to either block or character devices.
ERRORS
EFAULT The argument features a bad address.
EINVAL Invalid argument. EIO. An I/O error occurred.
EPERM Cannot create or delete a ramdisk without write permission on /dev/ramdiskctl.
ENOTTY The device does not support the requested ioctl function.
ENXIO The device did not exist during opening.
EBUSY Cannot exclusively open /dev/ramdiskctl. One or more ramdisks are still open.
EEXIST A ramdisk with the indicated name already exists.
EAGAIN Cannot allocate resource for ramdisk. Try again later.
FILES
/dev/ramdisk/diskname
Block device for ramdisk named diskname.
/dev/rramdisk/diskname
Raw device for ramdisk name diskname
/kernel/drv/ramdisk
32-bit driver
/kernel/drv/ramdisk.conf
Driver configuration file. (Do not alter).
/kernel/drv/sparcv9/ramdisk
64-bit driver
ATTRIBUTES
See attributes(5) for descriptions of the following attribute:
+-----------------------------+-----------------------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+-----------------------------+-----------------------------+
|Interface Stability |Evolving |
+-----------------------------+-----------------------------+
SEE ALSO ramdiskadm(1M), fsck(1M), fstyp(1M), mount(1M), newfs(1M), driver.conf(4), filesystem(5), dkio(7I)NOTES
The percentage of available physical memory that can be allocated to ramdisks is constrained by the variable rd_percent_physmem. You can
tune the rd_percent_physmem variable in /etc/system. By default, the percentage of available physical memory that can be allocated to
ramdisks is fixed at 25%.
A ramdisk may not be the best possible use of system memory. Accordingly, use ramdisks only when absolutely necessary.
SunOS 5.11 04 Mar 2003 ramdisk(7D)
Check Out this Related Man Page
RDEV(8) Linux Programmer's Manual RDEV(8)NAME
rdev - query/set image root device, RAM disk size, or video mode
SYNOPSIS
rdev [-Rrvh] [-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]]]
DESCRIPTION
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 offset 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 kernel image, might be:
/vmlinux
/vmunix
/boot/bzImage-2.4.0
/dev/fd0
/dev/fd1
When using the rdev command, the root_device parameter might be something like:
/dev/hda1
/dev/hdf13
/dev/sda2
/dev/sdc4
/dev/ida/c0d0p1
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. 2.0.x kernels and newer dynamically allocate
the ramdisk and do not need this setting.
For the rootflags command, the flags parameter contains extra information 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.
OPTIONS -r Causes rdev to act like ramsize (Not relevant for 2.0.x and newer kernels).
-R Causes rdev to act like rootflags.
-v Causes rdev to act like vidmode.
-h Provides help.
BUGS
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 architectures other than i386. Its use is strongly discouraged. Use a boot
loader like SysLinux or LILO instead.
HISTORY
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(2) system call.
At offset 504 there used to be the size of the ramdisk in kilobytes. One would specify a size, and this much was grabbed off the top of
memory. In Linux 1.1.39 it became also possible to set this value on the kernel command line. In Linux 1.3.48 the ramdisk setup was
changed. Ramdisk memory is now taken from the buffer cache, so that the ramdisk can grow dynamically. The interpretation of the ramdisk
word was changed to a word of which the high order bit is a prompt flag (1: prompt for ramdisk: "VFS: Insert ramdisk floppy and press
ENTER" - this is needed with a two-floppy boot), the next bit a load flag (1: load ramdisk), and the low order 11 bits give the starting
block number of the root filesystem image (so that one can have a single floppy boot). See also linux/Documentation/ramdisk.txt.
AUTHORS
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)
AVAILABILITY
The rdev command is part of the util-linux-ng package and is available from ftp://ftp.kernel.org/pub/linux/utils/util-linux-ng/.
Linux 0.99 20 November 1993 RDEV(8)