[PATCH v3 0/3] initrd: remove half of classic initrd support

[PATCH v3 0/3] initrd: remove half of classic initrd support

[Askar Safin]

Intro
====
This patchset removes half of classic initrd (initial RAM disk) support,
i. e. linuxrc code path, which was deprecated in 2020.
Initramfs still stays, RAM disk itself (brd) still stays.
And other half of initrd stays, too.
init/do_mounts* are listed in VFS entry in
MAINTAINERS, so I think this patchset should go through VFS tree.
I tested the patchset on 8 (!!!) archs in Qemu (see details below).
If you still use initrd, see below for workaround.

In 2020 deprecation notice was put to linuxrc initrd code path.
In v1 I tried to remove initrd
fully, but Nicolas Schichan reported that he still uses
other code path (root=/dev/ram0 one) on million devices [4].
root=/dev/ram0 code path did not contain deprecation notice.

So, in this version of patchset I remove deprecated code path,
i. e. linuxrc one, while keeping other, i. e. root=/dev/ram0 one.

Also I put deprecation notice to remaining code path, i. e. to
root=/dev/ram0 one. I plan to send patches for full removal
of initrd after one year, i. e. in September 2026 (of course,
initramfs will still work).

Also, I tried to make this patchset small to make sure it
can be reverted easily. I plan to send cleanups later.

Details
====
Other user-visible changes:

- Removed kernel command line parameters "load_ramdisk" and
"prompt_ramdisk", which did nothing and were deprecated
- Removed /proc/sys/kernel/real-root-dev . It was used
for initrd only
- Command line parameters "noinitrd" and "ramdisk_start=" are deprecated

This patchset is based on v6.18-rc1.

Testing
====
I tested my patchset on many architectures in Qemu using my Rust
program, heavily based on mkroot [1].

I used the following cross-compilers:

aarch64-linux-musleabi
armv4l-linux-musleabihf
armv5l-linux-musleabihf
armv7l-linux-musleabihf
i486-linux-musl
i686-linux-musl
mips-linux-musl
mips64-linux-musl
mipsel-linux-musl
powerpc-linux-musl
powerpc64-linux-musl
powerpc64le-linux-musl
riscv32-linux-musl
riscv64-linux-musl
s390x-linux-musl
sh4-linux-musl
sh4eb-linux-musl
x86_64-linux-musl

taken from this directory [2].

So, as you can see, there are 18 triplets, which correspond to 8 subdirs in arch/.

For every triplet I tested that:
- Initramfs still works (both builtin and external)
- Direct boot from disk still works
- Remaining initrd code path (root=/dev/ram0) still works

Workaround
====
If "retain_initrd" is passed to kernel, then initramfs/initrd,
passed by bootloader, is retained and becomes available after boot
as read-only magic file /sys/firmware/initrd [3].

No copies are involved. I. e. /sys/firmware/initrd is simply
a reference to original blob passed by bootloader.

This works even if initrd/initramfs is not recognized by kernel
in any way, i. e. even if it is not valid cpio archive, nor
a fs image supported by classic initrd.

This works both with my patchset and without it.

This means that you can emulate classic initrd so:
link builtin initramfs to kernel; in /init in this initramfs
copy /sys/firmware/initrd to some file in / and loop-mount it.

This is even better than classic initrd, because:
- You can use fs not supported by classic initrd, for example erofs
- One copy is involved (from /sys/firmware/initrd to some file in /)
as opposed to two when using classic initrd

Still, I don't recommend using this workaround, because
I want everyone to migrate to proper modern initramfs.
But still you can use this workaround if you want.

Also: it is not possible to directly loop-mount
/sys/firmware/initrd . Theoretically kernel can be changed
to allow this (and/or to make it writable), but I think nobody needs this.
And I don't want to implement this.

On Qemu's -initrd and GRUB's initrd
====
Don't panic, this patchset doesn't remove initramfs
(which is used by nearly all Linux distros). And I don't
have plans to remove it.

Qemu's -initrd option and GRUB's initrd command refer
to initrd bootloader mechanism, which is used to
load both initrd and (external) initramfs.

So, if you use Qemu's -initrd or GRUB's initrd,
then you likely use them to pass initramfs, and thus
you are safe.

v1: https://lore.kernel.org/lkml/20250913003842.41944-1-safinaskar@gmail.com/

v1 -> v2 changes:
- A lot. I removed most patches, see cover letter for details

v2: https://lore.kernel.org/lkml/20251010094047.3111495-1-safinaskar@gmail.com/

v2 -> v3 changes:
- Commit messages
- Expanded docs for "noinitrd"
- Added link to /sys/firmware/initrd workaround to pr_warn

[1] https://github.com/landley/toybox/tree/master/mkroot
[2] https://landley.net/toybox/downloads/binaries/toolchains/latest
[3] https://lore.kernel.org/all/20231207235654.16622-1-graf@amazon.com/
[4] https://lore.kernel.org/lkml/20250918152830.438554-1-nschichan@freebox.fr/

Askar Safin (3):
  init: remove deprecated "load_ramdisk" and "prompt_ramdisk" command
    line parameters
  initrd: remove deprecated code path (linuxrc)
  init: remove /proc/sys/kernel/real-root-dev

 .../admin-guide/kernel-parameters.txt         |  12 +-
 Documentation/admin-guide/sysctl/kernel.rst   |   6 -
 arch/arm/configs/neponset_defconfig           |   2 +-
 fs/init.c                                     |  14 ---
 include/linux/init_syscalls.h                 |   1 -
 include/linux/initrd.h                        |   2 -
 include/uapi/linux/sysctl.h                   |   1 -
 init/do_mounts.c                              |  11 +-
 init/do_mounts.h                              |  18 +--
 init/do_mounts_initrd.c                       | 107 ++----------------
 init/do_mounts_rd.c                           |  24 +---
 11 files changed, 23 insertions(+), 175 deletions(-)


base-commit: 3a8660878839faadb4f1a6dd72c3179c1df56787
-- 
2.47.3

[PATCH v3 1/3] init: remove deprecated "load_ramdisk" and "prompt_ramdisk" command line parameters

[Askar Safin]

...which do nothing. They were deprecated (in documentation) in
6b99e6e6aa62 ("Documentation/admin-guide: blockdev/ramdisk: remove use of
"rdev"") in 2020 and in kernel messages in c8376994c86c ("initrd: remove
support for multiple floppies") in 2020.

Signed-off-by: Askar Safin <safinaskar@gmail.com>
---
 Documentation/admin-guide/kernel-parameters.txt | 4 ----
 arch/arm/configs/neponset_defconfig             | 2 +-
 init/do_mounts.c                                | 7 -------
 init/do_mounts_rd.c                             | 7 -------
 4 files changed, 1 insertion(+), 19 deletions(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 6c42061ca20e..15af6933eab4 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -3319,8 +3319,6 @@
 			If there are multiple matching configurations changing
 			the same attribute, the last one is used.
 
-	load_ramdisk=	[RAM] [Deprecated]
-
 	lockd.nlm_grace_period=P  [NFS] Assign grace period.
 			Format: <integer>
 
@@ -5284,8 +5282,6 @@
 			Param: <number> - step/bucket size as a power of 2 for
 				statistical time based profiling.
 
-	prompt_ramdisk=	[RAM] [Deprecated]
-
 	prot_virt=	[S390] enable hosting protected virtual machines
 			isolated from the hypervisor (if hardware supports
 			that). If enabled, the default kernel base address
diff --git a/arch/arm/configs/neponset_defconfig b/arch/arm/configs/neponset_defconfig
index 2227f86100ad..4d720001c12e 100644
--- a/arch/arm/configs/neponset_defconfig
+++ b/arch/arm/configs/neponset_defconfig
@@ -9,7 +9,7 @@ CONFIG_ASSABET_NEPONSET=y
 CONFIG_ZBOOT_ROM_TEXT=0x80000
 CONFIG_ZBOOT_ROM_BSS=0xc1000000
 CONFIG_ZBOOT_ROM=y
-CONFIG_CMDLINE="console=ttySA0,38400n8 cpufreq=221200 rw root=/dev/mtdblock2 mtdparts=sa1100:512K(boot),1M(kernel),2560K(initrd),4M(root) load_ramdisk=1 prompt_ramdisk=0 mem=32M noinitrd initrd=0xc0800000,3M"
+CONFIG_CMDLINE="console=ttySA0,38400n8 cpufreq=221200 rw root=/dev/mtdblock2 mtdparts=sa1100:512K(boot),1M(kernel),2560K(initrd),4M(root) mem=32M noinitrd initrd=0xc0800000,3M"
 CONFIG_FPE_NWFPE=y
 CONFIG_PM=y
 CONFIG_MODULES=y
diff --git a/init/do_mounts.c b/init/do_mounts.c
index 6af29da8889e..0f2f44e6250c 100644
--- a/init/do_mounts.c
+++ b/init/do_mounts.c
@@ -34,13 +34,6 @@ static int root_wait;
 
 dev_t ROOT_DEV;
 
-static int __init load_ramdisk(char *str)
-{
-	pr_warn("ignoring the deprecated load_ramdisk= option\n");
-	return 1;
-}
-__setup("load_ramdisk=", load_ramdisk);
-
 static int __init readonly(char *str)
 {
 	if (*str)
diff --git a/init/do_mounts_rd.c b/init/do_mounts_rd.c
index 19d9f33dcacf..5311f2d7edc8 100644
--- a/init/do_mounts_rd.c
+++ b/init/do_mounts_rd.c
@@ -18,13 +18,6 @@
 static struct file *in_file, *out_file;
 static loff_t in_pos, out_pos;
 
-static int __init prompt_ramdisk(char *str)
-{
-	pr_warn("ignoring the deprecated prompt_ramdisk= option\n");
-	return 1;
-}
-__setup("prompt_ramdisk=", prompt_ramdisk);
-
 int __initdata rd_image_start;		/* starting block # of image */
 
 static int __init ramdisk_start_setup(char *str)
-- 
2.47.3

[PATCH v3 2/3] initrd: remove deprecated code path (linuxrc)

[Askar Safin]

Remove linuxrc initrd code path, which was deprecated in 2020.

Initramfs and (non-initial) RAM disks (i. e. brd) still work.

Both built-in and bootloader-supplied initramfs still work.

Non-linuxrc initrd code path (i. e. using /dev/ram as final root
filesystem) still works, but I put deprecation message into it.

Also I deprecate command line parameters "noinitrd" and "ramdisk_start=".

Signed-off-by: Askar Safin <safinaskar@gmail.com>
---
 .../admin-guide/kernel-parameters.txt         |  8 +-
 fs/init.c                                     | 14 ---
 include/linux/init_syscalls.h                 |  1 -
 include/linux/initrd.h                        |  2 -
 init/do_mounts.c                              |  4 +-
 init/do_mounts.h                              | 18 +---
 init/do_mounts_initrd.c                       | 87 ++-----------------
 init/do_mounts_rd.c                           | 17 +---
 8 files changed, 22 insertions(+), 129 deletions(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 15af6933eab4..df441d1a9555 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -4324,8 +4324,10 @@
 			Note that this argument takes precedence over
 			the CONFIG_RCU_NOCB_CPU_DEFAULT_ALL option.
 
-	noinitrd	[RAM] Tells the kernel not to load any configured
-			initial RAM disk.
+	noinitrd	[Deprecated,RAM] Tells the kernel not to load any configured
+			initial RAM disk. Currently this parameter applies to
+			initrd only, not to initramfs. But it applies to both
+			in EFI mode.
 
 	nointremap	[X86-64,Intel-IOMMU,EARLY] Do not enable interrupt
 			remapping.
@@ -5338,7 +5340,7 @@
 	ramdisk_size=	[RAM] Sizes of RAM disks in kilobytes
 			See Documentation/admin-guide/blockdev/ramdisk.rst.
 
-	ramdisk_start=	[RAM] RAM disk image start address
+	ramdisk_start=	[Deprecated,RAM] RAM disk image start address
 
 	random.trust_cpu=off
 			[KNL,EARLY] Disable trusting the use of the CPU's
diff --git a/fs/init.c b/fs/init.c
index 07f592ccdba8..60719494d9a0 100644
--- a/fs/init.c
+++ b/fs/init.c
@@ -27,20 +27,6 @@ int __init init_mount(const char *dev_name, const char *dir_name,
 	return ret;
 }
 
-int __init init_umount(const char *name, int flags)
-{
-	int lookup_flags = LOOKUP_MOUNTPOINT;
-	struct path path;
-	int ret;
-
-	if (!(flags & UMOUNT_NOFOLLOW))
-		lookup_flags |= LOOKUP_FOLLOW;
-	ret = kern_path(name, lookup_flags, &path);
-	if (ret)
-		return ret;
-	return path_umount(&path, flags);
-}
-
 int __init init_chdir(const char *filename)
 {
 	struct path path;
diff --git a/include/linux/init_syscalls.h b/include/linux/init_syscalls.h
index 92045d18cbfc..0bdbc458a881 100644
--- a/include/linux/init_syscalls.h
+++ b/include/linux/init_syscalls.h
@@ -2,7 +2,6 @@
 
 int __init init_mount(const char *dev_name, const char *dir_name,
 		const char *type_page, unsigned long flags, void *data_page);
-int __init init_umount(const char *name, int flags);
 int __init init_chdir(const char *filename);
 int __init init_chroot(const char *filename);
 int __init init_chown(const char *filename, uid_t user, gid_t group, int flags);
diff --git a/include/linux/initrd.h b/include/linux/initrd.h
index f1a1f4c92ded..7e5d26c8136f 100644
--- a/include/linux/initrd.h
+++ b/include/linux/initrd.h
@@ -3,8 +3,6 @@
 #ifndef __LINUX_INITRD_H
 #define __LINUX_INITRD_H
 
-#define INITRD_MINOR 250 /* shouldn't collide with /dev/ram* too soon ... */
-
 /* starting block # of image */
 extern int rd_image_start;
 
diff --git a/init/do_mounts.c b/init/do_mounts.c
index 0f2f44e6250c..1054ad3c905a 100644
--- a/init/do_mounts.c
+++ b/init/do_mounts.c
@@ -476,13 +476,11 @@ void __init prepare_namespace(void)
 	if (saved_root_name[0])
 		ROOT_DEV = parse_root_device(saved_root_name);
 
-	if (initrd_load(saved_root_name))
-		goto out;
+	initrd_load();
 
 	if (root_wait)
 		wait_for_root(saved_root_name);
 	mount_root(saved_root_name);
-out:
 	devtmpfs_mount();
 	init_mount(".", "/", NULL, MS_MOVE, NULL);
 	init_chroot(".");
diff --git a/init/do_mounts.h b/init/do_mounts.h
index 6069ea3eb80d..a386ee5314c9 100644
--- a/init/do_mounts.h
+++ b/init/do_mounts.h
@@ -23,25 +23,15 @@ static inline __init int create_dev(char *name, dev_t dev)
 }
 
 #ifdef CONFIG_BLK_DEV_RAM
-
-int __init rd_load_disk(int n);
-int __init rd_load_image(char *from);
-
+int __init rd_load_image(void);
 #else
-
-static inline int rd_load_disk(int n) { return 0; }
-static inline int rd_load_image(char *from) { return 0; }
-
+static inline int rd_load_image(void) { return 0; }
 #endif
 
 #ifdef CONFIG_BLK_DEV_INITRD
-bool __init initrd_load(char *root_device_name);
+void __init initrd_load(void);
 #else
-static inline bool initrd_load(char *root_device_name)
-{
-	return false;
-	}
-
+static inline void initrd_load(void) { }
 #endif
 
 /* Ensure that async file closing finished to prevent spurious errors. */
diff --git a/init/do_mounts_initrd.c b/init/do_mounts_initrd.c
index f6867bad0d78..bf381aa0400f 100644
--- a/init/do_mounts_initrd.c
+++ b/init/do_mounts_initrd.c
@@ -2,13 +2,7 @@
 #include <linux/unistd.h>
 #include <linux/kernel.h>
 #include <linux/fs.h>
-#include <linux/minix_fs.h>
-#include <linux/romfs_fs.h>
 #include <linux/initrd.h>
-#include <linux/sched.h>
-#include <linux/freezer.h>
-#include <linux/kmod.h>
-#include <uapi/linux/mount.h>
 
 #include "do_mounts.h"
 
@@ -41,6 +35,7 @@ late_initcall(kernel_do_mounts_initrd_sysctls_init);
 
 static int __init no_initrd(char *str)
 {
+	pr_warn("noinitrd option is deprecated and will be removed soon\n");
 	mount_initrd = 0;
 	return 1;
 }
@@ -70,85 +65,19 @@ static int __init early_initrd(char *p)
 }
 early_param("initrd", early_initrd);
 
-static int __init init_linuxrc(struct subprocess_info *info, struct cred *new)
-{
-	ksys_unshare(CLONE_FS | CLONE_FILES);
-	console_on_rootfs();
-	/* move initrd over / and chdir/chroot in initrd root */
-	init_chdir("/root");
-	init_mount(".", "/", NULL, MS_MOVE, NULL);
-	init_chroot(".");
-	ksys_setsid();
-	return 0;
-}
-
-static void __init handle_initrd(char *root_device_name)
-{
-	struct subprocess_info *info;
-	static char *argv[] = { "linuxrc", NULL, };
-	extern char *envp_init[];
-	int error;
-
-	pr_warn("using deprecated initrd support, will be removed soon.\n");
-
-	real_root_dev = new_encode_dev(ROOT_DEV);
-	create_dev("/dev/root.old", Root_RAM0);
-	/* mount initrd on rootfs' /root */
-	mount_root_generic("/dev/root.old", root_device_name,
-			   root_mountflags & ~MS_RDONLY);
-	init_mkdir("/old", 0700);
-	init_chdir("/old");
-
-	info = call_usermodehelper_setup("/linuxrc", argv, envp_init,
-					 GFP_KERNEL, init_linuxrc, NULL, NULL);
-	if (!info)
-		return;
-	call_usermodehelper_exec(info, UMH_WAIT_PROC|UMH_FREEZABLE);
-
-	/* move initrd to rootfs' /old */
-	init_mount("..", ".", NULL, MS_MOVE, NULL);
-	/* switch root and cwd back to / of rootfs */
-	init_chroot("..");
-
-	if (new_decode_dev(real_root_dev) == Root_RAM0) {
-		init_chdir("/old");
-		return;
-	}
-
-	init_chdir("/");
-	ROOT_DEV = new_decode_dev(real_root_dev);
-	mount_root(root_device_name);
-
-	printk(KERN_NOTICE "Trying to move old root to /initrd ... ");
-	error = init_mount("/old", "/root/initrd", NULL, MS_MOVE, NULL);
-	if (!error)
-		printk("okay\n");
-	else {
-		if (error == -ENOENT)
-			printk("/initrd does not exist. Ignored.\n");
-		else
-			printk("failed\n");
-		printk(KERN_NOTICE "Unmounting old root\n");
-		init_umount("/old", MNT_DETACH);
-	}
-}
-
-bool __init initrd_load(char *root_device_name)
+void __init initrd_load(void)
 {
 	if (mount_initrd) {
 		create_dev("/dev/ram", Root_RAM0);
 		/*
-		 * Load the initrd data into /dev/ram0. Execute it as initrd
-		 * unless /dev/ram0 is supposed to be our actual root device,
-		 * in that case the ram disk is just set up here, and gets
-		 * mounted in the normal path.
+		 * Load the initrd data into /dev/ram0.
 		 */
-		if (rd_load_image("/initrd.image") && ROOT_DEV != Root_RAM0) {
-			init_unlink("/initrd.image");
-			handle_initrd(root_device_name);
-			return true;
+		if (rd_load_image()) {
+			pr_warn("using deprecated initrd support, will be removed in September 2026; "
+				"use initramfs instead or (as a last resort) /sys/firmware/initrd; "
+				"see section \"Workaround\" in "
+				"https://lore.kernel.org/lkml/20251010094047.3111495-1-safinaskar@gmail.com\n");
 		}
 	}
 	init_unlink("/initrd.image");
-	return false;
 }
diff --git a/init/do_mounts_rd.c b/init/do_mounts_rd.c
index 5311f2d7edc8..0a021bbcd501 100644
--- a/init/do_mounts_rd.c
+++ b/init/do_mounts_rd.c
@@ -22,6 +22,7 @@ int __initdata rd_image_start;		/* starting block # of image */
 
 static int __init ramdisk_start_setup(char *str)
 {
+	pr_warn("ramdisk_start= option is deprecated and will be removed soon\n");
 	rd_image_start = simple_strtol(str,NULL,0);
 	return 1;
 }
@@ -177,7 +178,7 @@ static unsigned long nr_blocks(struct file *file)
 	return i_size_read(inode) >> 10;
 }
 
-int __init rd_load_image(char *from)
+int __init rd_load_image(void)
 {
 	int res = 0;
 	unsigned long rd_blocks, devblocks, nr_disks;
@@ -191,7 +192,7 @@ int __init rd_load_image(char *from)
 	if (IS_ERR(out_file))
 		goto out;
 
-	in_file = filp_open(from, O_RDONLY, 0);
+	in_file = filp_open("/initrd.image", O_RDONLY, 0);
 	if (IS_ERR(in_file))
 		goto noclose_input;
 
@@ -220,10 +221,7 @@ int __init rd_load_image(char *from)
 	/*
 	 * OK, time to copy in the data
 	 */
-	if (strcmp(from, "/initrd.image") == 0)
-		devblocks = nblocks;
-	else
-		devblocks = nr_blocks(in_file);
+	devblocks = nblocks;
 
 	if (devblocks == 0) {
 		printk(KERN_ERR "RAMDISK: could not determine device size\n");
@@ -267,13 +265,6 @@ int __init rd_load_image(char *from)
 	return res;
 }
 
-int __init rd_load_disk(int n)
-{
-	create_dev("/dev/root", ROOT_DEV);
-	create_dev("/dev/ram", MKDEV(RAMDISK_MAJOR, n));
-	return rd_load_image("/dev/root");
-}
-
 static int exit_code;
 static int decompress_error;
 
-- 
2.47.3

[PATCH v3 3/3] init: remove /proc/sys/kernel/real-root-dev

[Askar Safin]

It is not used anymore.

Signed-off-by: Askar Safin <safinaskar@gmail.com>
---
 Documentation/admin-guide/sysctl/kernel.rst |  6 ------
 include/uapi/linux/sysctl.h                 |  1 -
 init/do_mounts_initrd.c                     | 20 --------------------
 3 files changed, 27 deletions(-)

diff --git a/Documentation/admin-guide/sysctl/kernel.rst b/Documentation/admin-guide/sysctl/kernel.rst
index f3ee807b5d8b..218265babaf9 100644
--- a/Documentation/admin-guide/sysctl/kernel.rst
+++ b/Documentation/admin-guide/sysctl/kernel.rst
@@ -1215,12 +1215,6 @@ that support this feature.
 ==  ===========================================================================
 
 
-real-root-dev
-=============
-
-See Documentation/admin-guide/initrd.rst.
-
-
 reboot-cmd (SPARC only)
 =======================
 
diff --git a/include/uapi/linux/sysctl.h b/include/uapi/linux/sysctl.h
index 63d1464cb71c..1c7fe0f4dca4 100644
--- a/include/uapi/linux/sysctl.h
+++ b/include/uapi/linux/sysctl.h
@@ -92,7 +92,6 @@ enum
 	KERN_DOMAINNAME=8,	/* string: domainname */
 
 	KERN_PANIC=15,		/* int: panic timeout */
-	KERN_REALROOTDEV=16,	/* real root device to mount after initrd */
 
 	KERN_SPARC_REBOOT=21,	/* reboot command on Sparc */
 	KERN_CTLALTDEL=22,	/* int: allow ctl-alt-del to reboot */
diff --git a/init/do_mounts_initrd.c b/init/do_mounts_initrd.c
index bf381aa0400f..82613a3be756 100644
--- a/init/do_mounts_initrd.c
+++ b/init/do_mounts_initrd.c
@@ -8,31 +8,11 @@
 
 unsigned long initrd_start, initrd_end;
 int initrd_below_start_ok;
-static unsigned int real_root_dev;	/* do_proc_dointvec cannot handle kdev_t */
 static int __initdata mount_initrd = 1;
 
 phys_addr_t phys_initrd_start __initdata;
 unsigned long phys_initrd_size __initdata;
 
-#ifdef CONFIG_SYSCTL
-static const struct ctl_table kern_do_mounts_initrd_table[] = {
-	{
-		.procname       = "real-root-dev",
-		.data           = &real_root_dev,
-		.maxlen         = sizeof(int),
-		.mode           = 0644,
-		.proc_handler   = proc_dointvec,
-	},
-};
-
-static __init int kernel_do_mounts_initrd_sysctls_init(void)
-{
-	register_sysctl_init("kernel", kern_do_mounts_initrd_table);
-	return 0;
-}
-late_initcall(kernel_do_mounts_initrd_sysctls_init);
-#endif /* CONFIG_SYSCTL */
-
 static int __init no_initrd(char *str)
 {
 	pr_warn("noinitrd option is deprecated and will be removed soon\n");
-- 
2.47.3

Re: [PATCH v3 0/3] initrd: remove half of classic initrd support

[Christian Brauner]

On Fri, Oct 17, 2025 at 06:09:53AM +0000, Askar Safin wrote:
> Intro
> ====
> This patchset removes half of classic initrd (initial RAM disk) support,
> i. e. linuxrc code path, which was deprecated in 2020.
> Initramfs still stays, RAM disk itself (brd) still stays.
> And other half of initrd stays, too.
> init/do_mounts* are listed in VFS entry in
> MAINTAINERS, so I think this patchset should go through VFS tree.
> I tested the patchset on 8 (!!!) archs in Qemu (see details below).
> If you still use initrd, see below for workaround.
> 
> In 2020 deprecation notice was put to linuxrc initrd code path.
> In v1 I tried to remove initrd
> fully, but Nicolas Schichan reported that he still uses
> other code path (root=/dev/ram0 one) on million devices [4].
> root=/dev/ram0 code path did not contain deprecation notice.

Without Acks or buy-in from other maintainers this is not a change we
can just do given that a few people already piped up and expressed
reservations that this would be doable for them.

@Christoph, you marked this as deprecated years ago.
What's your take on this?

> 
> So, in this version of patchset I remove deprecated code path,
> i. e. linuxrc one, while keeping other, i. e. root=/dev/ram0 one.
> 
> Also I put deprecation notice to remaining code path, i. e. to
> root=/dev/ram0 one. I plan to send patches for full removal
> of initrd after one year, i. e. in September 2026 (of course,
> initramfs will still work).
> 
> Also, I tried to make this patchset small to make sure it
> can be reverted easily. I plan to send cleanups later.
> 
> Details
> ====
> Other user-visible changes:
> 
> - Removed kernel command line parameters "load_ramdisk" and
> "prompt_ramdisk", which did nothing and were deprecated
> - Removed /proc/sys/kernel/real-root-dev . It was used
> for initrd only
> - Command line parameters "noinitrd" and "ramdisk_start=" are deprecated
> 
> This patchset is based on v6.18-rc1.
> 
> Testing
> ====
> I tested my patchset on many architectures in Qemu using my Rust
> program, heavily based on mkroot [1].
> 
> I used the following cross-compilers:
> 
> aarch64-linux-musleabi
> armv4l-linux-musleabihf
> armv5l-linux-musleabihf
> armv7l-linux-musleabihf
> i486-linux-musl
> i686-linux-musl
> mips-linux-musl
> mips64-linux-musl
> mipsel-linux-musl
> powerpc-linux-musl
> powerpc64-linux-musl
> powerpc64le-linux-musl
> riscv32-linux-musl
> riscv64-linux-musl
> s390x-linux-musl
> sh4-linux-musl
> sh4eb-linux-musl
> x86_64-linux-musl
> 
> taken from this directory [2].
> 
> So, as you can see, there are 18 triplets, which correspond to 8 subdirs in arch/.
> 
> For every triplet I tested that:
> - Initramfs still works (both builtin and external)
> - Direct boot from disk still works
> - Remaining initrd code path (root=/dev/ram0) still works
> 
> Workaround
> ====
> If "retain_initrd" is passed to kernel, then initramfs/initrd,
> passed by bootloader, is retained and becomes available after boot
> as read-only magic file /sys/firmware/initrd [3].
> 
> No copies are involved. I. e. /sys/firmware/initrd is simply
> a reference to original blob passed by bootloader.
> 
> This works even if initrd/initramfs is not recognized by kernel
> in any way, i. e. even if it is not valid cpio archive, nor
> a fs image supported by classic initrd.
> 
> This works both with my patchset and without it.
> 
> This means that you can emulate classic initrd so:
> link builtin initramfs to kernel; in /init in this initramfs
> copy /sys/firmware/initrd to some file in / and loop-mount it.
> 
> This is even better than classic initrd, because:
> - You can use fs not supported by classic initrd, for example erofs
> - One copy is involved (from /sys/firmware/initrd to some file in /)
> as opposed to two when using classic initrd
> 
> Still, I don't recommend using this workaround, because
> I want everyone to migrate to proper modern initramfs.
> But still you can use this workaround if you want.
> 
> Also: it is not possible to directly loop-mount
> /sys/firmware/initrd . Theoretically kernel can be changed
> to allow this (and/or to make it writable), but I think nobody needs this.
> And I don't want to implement this.
> 
> On Qemu's -initrd and GRUB's initrd
> ====
> Don't panic, this patchset doesn't remove initramfs
> (which is used by nearly all Linux distros). And I don't
> have plans to remove it.
> 
> Qemu's -initrd option and GRUB's initrd command refer
> to initrd bootloader mechanism, which is used to
> load both initrd and (external) initramfs.
> 
> So, if you use Qemu's -initrd or GRUB's initrd,
> then you likely use them to pass initramfs, and thus
> you are safe.
> 
> v1: https://lore.kernel.org/lkml/20250913003842.41944-1-safinaskar@gmail.com/
> 
> v1 -> v2 changes:
> - A lot. I removed most patches, see cover letter for details
> 
> v2: https://lore.kernel.org/lkml/20251010094047.3111495-1-safinaskar@gmail.com/
> 
> v2 -> v3 changes:
> - Commit messages
> - Expanded docs for "noinitrd"
> - Added link to /sys/firmware/initrd workaround to pr_warn
> 
> [1] https://github.com/landley/toybox/tree/master/mkroot
> [2] https://landley.net/toybox/downloads/binaries/toolchains/latest
> [3] https://lore.kernel.org/all/20231207235654.16622-1-graf@amazon.com/
> [4] https://lore.kernel.org/lkml/20250918152830.438554-1-nschichan@freebox.fr/
> 
> Askar Safin (3):
>   init: remove deprecated "load_ramdisk" and "prompt_ramdisk" command
>     line parameters
>   initrd: remove deprecated code path (linuxrc)
>   init: remove /proc/sys/kernel/real-root-dev
> 
>  .../admin-guide/kernel-parameters.txt         |  12 +-
>  Documentation/admin-guide/sysctl/kernel.rst   |   6 -
>  arch/arm/configs/neponset_defconfig           |   2 +-
>  fs/init.c                                     |  14 ---
>  include/linux/init_syscalls.h                 |   1 -
>  include/linux/initrd.h                        |   2 -
>  include/uapi/linux/sysctl.h                   |   1 -
>  init/do_mounts.c                              |  11 +-
>  init/do_mounts.h                              |  18 +--
>  init/do_mounts_initrd.c                       | 107 ++----------------
>  init/do_mounts_rd.c                           |  24 +---
>  11 files changed, 23 insertions(+), 175 deletions(-)
> 
> 
> base-commit: 3a8660878839faadb4f1a6dd72c3179c1df56787
> -- 
> 2.47.3
> 

Re: [PATCH v3 2/3] initrd: remove deprecated code path (linuxrc)

[Bagas Sanjaya]

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On Fri, Oct 17, 2025 at 06:09:55AM +0000, Askar Safin wrote:
> +		if (rd_load_image()) {
> +			pr_warn("using deprecated initrd support, will be removed in September 2026; "
> +				"use initramfs instead or (as a last resort) /sys/firmware/initrd; "
> +				"see section \"Workaround\" in "
> +				"https://lore.kernel.org/lkml/20251010094047.3111495-1-safinaskar@gmail.com\n");
>  		}

Do you mean that initrd support will be removed in LTS kernel release of 2026?

Thanks. 

-- 
An old man doll... just what I always wanted! - Clara

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Re: [PATCH v3 0/3] initrd: remove half of classic initrd support

[Christoph Hellwig]

On Tue, Oct 21, 2025 at 03:05:35PM +0200, Christian Brauner wrote:
> Without Acks or buy-in from other maintainers this is not a change we
> can just do given that a few people already piped up and expressed
> reservations that this would be doable for them.
> 
> @Christoph, you marked this as deprecated years ago.
> What's your take on this?

I'd love to see it go obviously.  But IIRC we had various users show
up, which speaks against removing it.  Maybe the first step would be
a separate config option just for block-based initrd?

Re: [PATCH v3 2/3] initrd: remove deprecated code path (linuxrc)

[Askar Safin]

Bagas Sanjaya <bagasdotme@gmail.com>:
> Do you mean that initrd support will be removed in LTS kernel release of 2026?

I meant September 2026. But okay, if there is v4, then I will change this to
"after LTS release in the end of 2026".

-- 
Askar Safin

Re: [PATCH v3 0/3] initrd: remove half of classic initrd support

[Askar Safin]

Christoph Hellwig <hch@infradead.org>:
> On Tue, Oct 21, 2025 at 03:05:35PM +0200, Christian Brauner wrote:
> > Without Acks or buy-in from other maintainers this is not a change we
> > can just do given that a few people already piped up and expressed
> > reservations that this would be doable for them.
> > 
> > @Christoph, you marked this as deprecated years ago.
> > What's your take on this?
> 
> I'd love to see it go obviously.  But IIRC we had various users show
> up, which speaks against removing it.  Maybe the first step would be
> a separate config option just for block-based initrd?

So far in recent months 3 people spoke against initrd removal. All they are in Cc. They are:

- Julian Stecklina. He planned to use initrd with erofs, which is currently
not supported anyway. Also, he replied to v1:
"You have all my support for nuking so much legacy code!"
"Acked-by: Julian Stecklina <julian.stecklina@cyberus-technology.de>"
( https://lore.kernel.org/lkml/1f9aee6090716db537e9911685904786b030111f.camel@cyberus-technology.de/ )

- Gao Xiang, maintainer of erofs. He also planned to use initrd with erofs,
which is currently not supported anyway. Also, he said to me:
> Again, I don't have any strong opinion to kill initrd entirely because
> I think initdax may be more efficient and I don't have any time to work
> on this part -- it's unrelated to my job.
( https://lore.kernel.org/all/79315382-5ba8-42c1-ad03-5cb448b23b72@linux.alibaba.com/ )

- Nicolas Schichan. He has million devices, which use initrd. But they use
root=/dev/ram code path, not linuxrc code path, which I'm removing. He
explained this here:
https://lore.kernel.org/lkml/20250918152830.438554-1-nschichan@freebox.fr/

So, this patchset will not impact these people. So, I think it is okay
to remove linuxrc now. We can revert this patchset if needed.

-- 
Askar Safin

Re: [PATCH v3 2/3] initrd: remove deprecated code path (linuxrc)

[Andy Shevchenko]

On Wed, Oct 22, 2025 at 11:06 AM Askar Safin <safinaskar@gmail.com> wrote:
> Bagas Sanjaya <bagasdotme@gmail.com>:

...

> > Do you mean that initrd support will be removed in LTS kernel release of 2026?
>
> I meant September 2026. But okay, if there is v4, then I will change this to
> "after LTS release in the end of 2026".

No need to mention "ater LTS release", we all know that this is the
last release that made the year in question.

-- 
With Best Regards,
Andy Shevchenko