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Message-ID: <20250913003842.41944-16-safinaskar@gmail.com> Date: Sat, 13 Sep 2025 00:37:54 +0000 From: Askar Safin <safinaskar@...il.com> To: linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org Cc: Linus Torvalds <torvalds@...ux-foundation.org>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Christian Brauner <brauner@...nel.org>, Al Viro <viro@...iv.linux.org.uk>, Jan Kara <jack@...e.cz>, Christoph Hellwig <hch@....de>, Jens Axboe <axboe@...nel.dk>, Andy Shevchenko <andy.shevchenko@...il.com>, Aleksa Sarai <cyphar@...har.com>, Thomas Weißschuh <thomas.weissschuh@...utronix.de>, Julian Stecklina <julian.stecklina@...erus-technology.de>, Gao Xiang <hsiangkao@...ux.alibaba.com>, Art Nikpal <email2tema@...il.com>, Andrew Morton <akpm@...ux-foundation.org>, Eric Curtin <ecurtin@...hat.com>, Alexander Graf <graf@...zon.com>, Rob Landley <rob@...dley.net>, Lennart Poettering <mzxreary@...inter.de>, linux-arch@...r.kernel.org, linux-alpha@...r.kernel.org, linux-snps-arc@...ts.infradead.org, linux-arm-kernel@...ts.infradead.org, linux-csky@...r.kernel.org, linux-hexagon@...r.kernel.org, loongarch@...ts.linux.dev, linux-m68k@...ts.linux-m68k.org, linux-mips@...r.kernel.org, linux-openrisc@...r.kernel.org, linux-parisc@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org, linux-riscv@...ts.infradead.org, linux-s390@...r.kernel.org, linux-sh@...r.kernel.org, sparclinux@...r.kernel.org, linux-um@...ts.infradead.org, x86@...nel.org, Ingo Molnar <mingo@...hat.com>, linux-block@...r.kernel.org, initramfs@...r.kernel.org, linux-api@...r.kernel.org, linux-doc@...r.kernel.org, linux-efi@...r.kernel.org, linux-ext4@...r.kernel.org, "Theodore Y . Ts'o" <tytso@....edu>, linux-acpi@...r.kernel.org, Michal Simek <monstr@...str.eu>, devicetree@...r.kernel.org, Luis Chamberlain <mcgrof@...nel.org>, Kees Cook <kees@...nel.org>, Thorsten Blum <thorsten.blum@...ux.dev>, Heiko Carstens <hca@...ux.ibm.com>, patches@...ts.linux.dev Subject: [PATCH RESEND 15/62] doc: modernize Documentation/admin-guide/blockdev/ramdisk.rst Update it to reflect initrd removal Signed-off-by: Askar Safin <safinaskar@...il.com> --- .../admin-guide/blockdev/ramdisk.rst | 103 ++---------------- 1 file changed, 7 insertions(+), 96 deletions(-) diff --git a/Documentation/admin-guide/blockdev/ramdisk.rst b/Documentation/admin-guide/blockdev/ramdisk.rst index e57c61108dbc..6289e085f18f 100644 --- a/Documentation/admin-guide/blockdev/ramdisk.rst +++ b/Documentation/admin-guide/blockdev/ramdisk.rst @@ -5,18 +5,14 @@ Using the RAM disk block device with Linux .. Contents: 1) Overview - 2) Kernel Command Line Parameters - 3) Using "rdev" - 4) An Example of Creating a Compressed RAM Disk + 2) Module parameters 1) Overview ----------- -The RAM disk driver is a way to use main system memory as a block device. It -is required for initrd, an initial filesystem used if you need to load modules -in order to access the root filesystem (see Documentation/admin-guide/initrd.rst). It can -also be used for a temporary filesystem for crypto work, since the contents +The RAM disk driver is a way to use main system memory as a block device. +It can also be used for a temporary filesystem for crypto work, since the contents are erased on reboot. The RAM disk dynamically grows as more space is required. It does this by using @@ -30,109 +26,24 @@ and (re)build the kernel. To use RAM disk support with your system, run './MAKEDEV ram' from the /dev directory. RAM disks are all major number 1, and start with minor number 0 -for /dev/ram0, etc. If used, modern kernels use /dev/ram0 for an initrd. - -The new RAM disk also has the ability to load compressed RAM disk images, -allowing one to squeeze more programs onto an average installation or -rescue floppy disk. +for /dev/ram0, etc. -2) Parameters ---------------------------------- +2) Module parameters +-------------------- -2a) Kernel Command Line Parameters - - ramdisk_size=N + rd_size=N Size of the ramdisk. This parameter tells the RAM disk driver to set up RAM disks of N k size. The default is 4096 (4 MB). -2b) Module parameters - rd_nr /dev/ramX devices created. max_part Maximum partition number. - rd_size - See ramdisk_size. - -3) Using "rdev" ---------------- - -"rdev" is an obsolete, deprecated, antiquated utility that could be used -to set the boot device in a Linux kernel image. - -Instead of using rdev, just place the boot device information on the -kernel command line and pass it to the kernel from the bootloader. - -You can also pass arguments to the kernel by setting FDARGS in -arch/x86/boot/Makefile and specify in initrd image by setting FDINITRD in -arch/x86/boot/Makefile. - -Some of the kernel command line boot options that may apply here are:: - - ramdisk_size=M - -If you make a boot disk that has LILO, then for the above, you would use:: - - append = "ramdisk_size=M" - -4) An Example of Creating a Compressed RAM Disk ------------------------------------------------ - -To create a RAM disk image, you will need a spare block device to -construct it on. This can be the RAM disk device itself, or an -unused disk partition (such as an unmounted swap partition). For this -example, we will use the RAM disk device, "/dev/ram0". - -Note: This technique should not be done on a machine with less than 8 MB -of RAM. If using a spare disk partition instead of /dev/ram0, then this -restriction does not apply. - -a) Decide on the RAM disk size that you want. Say 2 MB for this example. - Create it by writing to the RAM disk device. (This step is not currently - required, but may be in the future.) It is wise to zero out the - area (esp. for disks) so that maximal compression is achieved for - the unused blocks of the image that you are about to create:: - - dd if=/dev/zero of=/dev/ram0 bs=1k count=2048 - -b) Make a filesystem on it. Say ext2fs for this example:: - - mke2fs -vm0 /dev/ram0 2048 - -c) Mount it, copy the files you want to it (eg: /etc/* /dev/* ...) - and unmount it again. - -d) Compress the contents of the RAM disk. The level of compression - will be approximately 50% of the space used by the files. Unused - space on the RAM disk will compress to almost nothing:: - - dd if=/dev/ram0 bs=1k count=2048 | gzip -v9 > /tmp/ram_image.gz - -e) Put the kernel onto the floppy:: - - dd if=zImage of=/dev/fd0 bs=1k - -f) Put the RAM disk image onto the floppy, after the kernel. Use an offset - that is slightly larger than the kernel, so that you can put another - (possibly larger) kernel onto the same floppy later without overlapping - the RAM disk image. An offset of 400 kB for kernels about 350 kB in - size would be reasonable. Make sure offset+size of ram_image.gz is - not larger than the total space on your floppy (usually 1440 kB):: - - dd if=/tmp/ram_image.gz of=/dev/fd0 bs=1k seek=400 - -g) Make sure that you have already specified the boot information in - FDARGS and FDINITRD or that you use a bootloader to pass kernel - command line boot options to the kernel. - -That is it. You now have your boot/root compressed RAM disk floppy. Some -users may wish to combine steps (d) and (f) by using a pipe. - Paul Gortmaker 12/95 -- 2.47.2
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