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diff --git a/man4/initrd.4 b/man4/initrd.4 deleted file mode 100644 index 1490f8e..0000000 --- a/man4/initrd.4 +++ /dev/null @@ -1,479 +0,0 @@ -.\" This man-page is Copyright (C) 1997 John S. Kallal -.\" -.\" SPDX-License-Identifier: Linux-man-pages-copyleft -.\" -.\" If the you wish to distribute versions of this work under other -.\" conditions than the above, please contact the author(s) at the following -.\" for permission: -.\" -.\" John S. Kallal - -.\" email: <kallal@voicenet.com> -.\" mail: 518 Kerfoot Farm RD, Wilmington, DE 19803-2444, USA -.\" phone: (302)654-5478 -.\" -.\" $Id: initrd.4,v 0.9 1997/11/07 05:05:32 kallal Exp kallal $ -.TH initrd 4 2023-10-31 "Linux man-pages 6.7" -.SH NAME -initrd \- boot loader initialized RAM disk -.SH CONFIGURATION -.I /dev/initrd -is a read-only block device assigned -major number 1 and minor number 250. -Typically -.I /dev/initrd -is owned by -root:disk -with mode 0400 (read access by root only). -If the Linux system does not have -.I /dev/initrd -already created, it can be created with the following commands: -.P -.in +4n -.EX -mknod \-m 400 /dev/initrd b 1 250 -chown root:disk /dev/initrd -.EE -.in -.P -Also, support for both "RAM disk" and "Initial RAM disk" -(e.g., -.B CONFIG_BLK_DEV_RAM=y -and -.BR CONFIG_BLK_DEV_INITRD=y ) -must be compiled directly into the Linux kernel to use -.IR /dev/initrd . -When using -.IR /dev/initrd , -the RAM disk driver cannot be loaded as a module. -.\" -.\" -.\" -.SH DESCRIPTION -The special file -.I /dev/initrd -is a read-only block device. -This device is a RAM disk that is initialized (e.g., loaded) -by the boot loader before the kernel is started. -The kernel then can use -.IR /dev/initrd "'s" -contents for a two-phase system boot-up. -.P -In the first boot-up phase, the kernel starts up -and mounts an initial root filesystem from the contents of -.I /dev/initrd -(e.g., RAM disk initialized by the boot loader). -In the second phase, additional drivers or other modules -are loaded from the initial root device's contents. -After loading the additional modules, a new root filesystem -(i.e., the normal root filesystem) is mounted from a -different device. -.\" -.\" -.\" -.SS Boot-up operation -When booting up with -.BR initrd , -the system boots as follows: -.IP (1) 5 -The boot loader loads the kernel program and -.IR /dev/initrd 's -contents into memory. -.IP (2) -On kernel startup, -the kernel uncompresses and copies the contents of the device -.I /dev/initrd -onto device -.I /dev/ram0 -and then frees the memory used by -.IR /dev/initrd . -.IP (3) -The kernel then read-write mounts the device -.I /dev/ram0 -as the initial root filesystem. -.IP (4) -If the indicated normal root filesystem is also the initial -root filesystem (e.g., -.IR /dev/ram0 ) -then the kernel skips to the last step for the usual boot sequence. -.IP (5) -If the executable file -.I /linuxrc -is present in the initial root filesystem, -.I /linuxrc -is executed with UID 0. -(The file -.I /linuxrc -must have executable permission. -The file -.I /linuxrc -can be any valid executable, including a shell script.) -.IP (6) -If -.I /linuxrc -is not executed or when -.I /linuxrc -terminates, the normal root filesystem is mounted. -(If -.I /linuxrc -exits with any filesystems mounted on the initial root -filesystem, then the behavior of the kernel is -.BR UNSPECIFIED . -See the NOTES section for the current kernel behavior.) -.IP (7) -If the normal root filesystem has a directory -.IR /initrd , -the device -.I /dev/ram0 -is moved from -.I / -to -.IR /initrd . -Otherwise, if the directory -.I /initrd -does not exist, the device -.I /dev/ram0 -is unmounted. -(When moved from -.I / -to -.IR /initrd , -.I /dev/ram0 -is not unmounted and therefore processes can remain running from -.IR /dev/ram0 . -If directory -.I /initrd -does not exist on the normal root filesystem -and any processes remain running from -.I /dev/ram0 -when -.I /linuxrc -exits, the behavior of the kernel is -.BR UNSPECIFIED . -See the NOTES section for the current kernel behavior.) -.IP (8) -The usual boot sequence (e.g., invocation of -.IR /sbin/init ) -is performed on the normal root filesystem. -.\" -.\" -.\" -.SS Options -The following boot loader options, when used with -.BR initrd , -affect the kernel's boot-up operation: -.TP -.BI initrd= "filename" -Specifies the file to load as the contents of -.IR /dev/initrd . -For -.B LOADLIN -this is a command-line option. -For -.B LILO -you have to use this command in the -.B LILO -configuration file -.IR /etc/lilo.config . -The filename specified with this -option will typically be a gzipped filesystem image. -.TP -.B noinitrd -This boot option disables the two-phase boot-up operation. -The kernel performs the usual boot sequence as if -.I /dev/initrd -was not initialized. -With this option, any contents of -.I /dev/initrd -loaded into memory by the boot loader contents are preserved. -This option permits the contents of -.I /dev/initrd -to be any data and need not be limited to a filesystem image. -However, device -.I /dev/initrd -is read-only and can be read only one time after system startup. -.TP -.BI root= "device-name" -Specifies the device to be used as the normal root filesystem. -For -.B LOADLIN -this is a command-line option. -For -.B LILO -this is a boot time option or -can be used as an option line in the -.B LILO -configuration file -.IR /etc/lilo.config . -The device specified by this option must be a mountable -device having a suitable root filesystem. -.\" -.\" -.\" -.SS Changing the normal root filesystem -By default, -the kernel's settings -(e.g., set in the kernel file with -.BR rdev (8) -or compiled into the kernel file), -or the boot loader option setting -is used for the normal root filesystems. -For an NFS-mounted normal root filesystem, one has to use the -.B nfs_root_name -and -.B nfs_root_addrs -boot options to give the NFS settings. -For more information on NFS-mounted root see the kernel documentation file -.I Documentation/filesystems/nfs/nfsroot.txt -.\" commit dc7a08166f3a5f23e79e839a8a88849bd3397c32 -(or -.I Documentation/filesystems/nfsroot.txt -before Linux 2.6.33). -For more information on setting the root filesystem see also the -.B LILO -and -.B LOADLIN -documentation. -.P -It is also possible for the -.I /linuxrc -executable to change the normal root device. -For -.I /linuxrc -to change the normal root device, -.I /proc -must be mounted. -After mounting -.IR /proc , -.I /linuxrc -changes the normal root device by writing into the proc files -.IR /proc/sys/kernel/real\-root\-dev , -.IR /proc/sys/kernel/nfs\-root\-name , -and -.IR /proc/sys/kernel/nfs\-root\-addrs . -For a physical root device, the root device is changed by having -.I /linuxrc -write the new root filesystem device number into -.IR /proc/sys/kernel/real\-root\-dev . -For an NFS root filesystem, the root device is changed by having -.I /linuxrc -write the NFS setting into files -.I /proc/sys/kernel/nfs\-root\-name -and -.I /proc/sys/kernel/nfs\-root\-addrs -and then writing 0xff (e.g., the pseudo-NFS-device number) into file -.IR /proc/sys/kernel/real\-root\-dev . -For example, the following shell command line would change -the normal root device to -.IR /dev/hdb1 : -.P -.in +4n -.EX -echo 0x365 >/proc/sys/kernel/real\-root\-dev -.EE -.in -.P -For an NFS example, the following shell command lines would change the -normal root device to the NFS directory -.I /var/nfsroot -on a local networked NFS server with IP number 193.8.232.7 for a system with -IP number 193.8.232.2 and named "idefix": -.P -.in +4n -.EX -echo /var/nfsroot >/proc/sys/kernel/nfs\-root\-name -echo 193.8.232.2:193.8.232.7::255.255.255.0:idefix \e - >/proc/sys/kernel/nfs\-root\-addrs -echo 255 >/proc/sys/kernel/real\-root\-dev -.EE -.in -.P -.BR Note : -The use of -.I /proc/sys/kernel/real\-root\-dev -to change the root filesystem is obsolete. -See the Linux kernel source file -.I Documentation/admin\-guide/initrd.rst -.\" commit 9d85025b0418163fae079c9ba8f8445212de8568 -(or -.I Documentation/initrd.txt -before Linux 4.10) -as well as -.BR pivot_root (2) -and -.BR pivot_root (8) -for information on the modern method of changing the root filesystem. -.\" FIXME . Should this manual page describe the pivot_root mechanism? -.\" -.\" -.\" -.SS Usage -The main motivation for implementing -.B initrd -was to allow for modular kernel configuration at system installation. -.P -A possible system installation scenario is as follows: -.IP (1) 5 -The loader program boots from floppy or other media with a minimal kernel -(e.g., support for -.IR /dev/ram , -.IR /dev/initrd , -and the ext2 filesystem) and loads -.I /dev/initrd -with a gzipped version of the initial filesystem. -.IP (2) -The executable -.I /linuxrc -determines what is needed to (1) mount the normal root filesystem -(i.e., device type, device drivers, filesystem) and (2) the -distribution media (e.g., CD-ROM, network, tape, ...). -This can be done by asking the user, by auto-probing, -or by using a hybrid approach. -.IP (3) -The executable -.I /linuxrc -loads the necessary modules from the initial root filesystem. -.IP (4) -The executable -.I /linuxrc -creates and populates the root filesystem. -(At this stage the normal root filesystem does not have to be a -completed system yet.) -.IP (5) -The executable -.I /linuxrc -sets -.IR /proc/sys/kernel/real\-root\-dev , -unmounts -.IR /proc , -the normal root filesystem and any other filesystems -it has mounted, and then terminates. -.IP (6) -The kernel then mounts the normal root filesystem. -.IP (7) -Now that the filesystem is accessible and intact, -the boot loader can be installed. -.IP (8) -The boot loader is configured to load into -.I /dev/initrd -a filesystem with the set of modules that was used to bring up the system. -(e.g., device -.I /dev/ram0 -can be modified, then unmounted, and finally, the image is written from -.I /dev/ram0 -to a file.) -.IP (9) -The system is now bootable and additional installation tasks can be -performed. -.P -The key role of -.I /dev/initrd -in the above is to reuse the configuration data during normal system operation -without requiring initial kernel selection, a large generic kernel or, -recompiling the kernel. -.P -A second scenario is for installations where Linux runs on systems with -different hardware configurations in a single administrative network. -In such cases, it may be desirable to use only a small set of kernels -(ideally only one) and to keep the system-specific part of configuration -information as small as possible. -In this case, create a common file -with all needed modules. -Then, only the -.I /linuxrc -file or a file executed by -.I /linuxrc -would be different. -.P -A third scenario is more convenient recovery disks. -Because information like the location of the root filesystem -partition is not needed at boot time, the system loaded from -.I /dev/initrd -can use a dialog and/or auto-detection followed by a -possible sanity check. -.P -Last but not least, Linux distributions on CD-ROM may use -.B initrd -for easy installation from the CD-ROM. -The distribution can use -.B LOADLIN -to directly load -.I /dev/initrd -from CD-ROM without the need of any floppies. -The distribution could also use a -.B LILO -boot floppy and then bootstrap a bigger RAM disk via -.I /dev/initrd -from the CD-ROM. -.\" -.\" -.\" -.SH FILES -.I /dev/initrd -.br -.I /dev/ram0 -.br -.I /linuxrc -.br -.I /initrd -.\" -.\" -.\" -.SH NOTES -.IP \[bu] 3 -With the current kernel, any filesystems that remain mounted when -.I /dev/ram0 -is moved from -.I / -to -.I /initrd -continue to be accessible. -However, the -.I /proc/mounts -entries are not updated. -.IP \[bu] -With the current kernel, if directory -.I /initrd -does not exist, then -.I /dev/ram0 -will -.B not -be fully unmounted if -.I /dev/ram0 -is used by any process or has any filesystem mounted on it. -If -.I /dev/ram0 -is -.B not -fully unmounted, then -.I /dev/ram0 -will remain in memory. -.IP \[bu] -Users of -.I /dev/initrd -should not depend on the behavior given in the above notes. -The behavior may change in future versions of the Linux kernel. -.\" -.\" -.\" -.\" .SH AUTHORS -.\" The kernel code for device -.\" .BR initrd -.\" was written by Werner Almesberger <almesber@lrc.epfl.ch> and -.\" Hans Lermen <lermen@elserv.ffm.fgan.de>. -.\" The code for -.\" .BR initrd -.\" was added to the baseline Linux kernel in development version 1.3.73. -.SH SEE ALSO -.BR chown (1), -.BR mknod (1), -.BR ram (4), -.BR freeramdisk (8), -.BR rdev (8) -.P -.I Documentation/admin\-guide/initrd.rst -.\" commit 9d85025b0418163fae079c9ba8f8445212de8568 -(or -.I Documentation/initrd.txt -before Linux 4.10) -in the Linux kernel source tree, the LILO documentation, -the LOADLIN documentation, the SYSLINUX documentation |