pcinitrd(8) [redhat man page]
PCINITRD(8) System Manager's Manual PCINITRD(8) NAME
pcinitrd - create a PCMCIA initrd ram disk image SYNOPSIS
pcinitrd [-v] [-a] [--all] [-d alternate-root] [--dir=alternate-root] [-r kernel-release] [--release=kernel-release] [-s image-size] [--size=image-size] [-u] [--update] initrd-image [modules ...] DESCRIPTION
The pcinitrd script creates an initrd ram disk image for booting with the root filesystem on a PCMCIA device. If the target is a block special device (i.e., /dev/fd0), then the initrd image is created on that device. If the target does not already exist or if it is an ordinary file, then pcinitrd will create the image file using the ``loopback'' device. Modules are specified with paths relative to /lib/modules/[kernel-release]. The core PCMCIA modules (pcmcia/pcmcia_core and pcmcia/ds) will automatically be installed in the target image. All other device-specific modules need to be listed on the command line, along with the appropriate socket driver (pcmcia/i82365.o or pcmcia/tcic.o). Alternatively, if -a is specified, then all available PCMCIA socket drivers and block device drivers will be included in the image. Additional files to be copied to the initrd image may also be listed on the command line. Executable programs will be installed in /bin, shared libraries will be installed in /lib, device files will be installed in /dev, and any other files will be placed in /etc. The startup script in the resulting image, linuxrc, may need to be customized for a particular system. It contains the same variable defi- nitions as the normal PCMCIA startup scripts (i.e., PCIC=, PCIC_OPTS=, and CORE_OPTS= variables). The /etc/config.opts file may also need to be edited. Any changes to linuxrc or config.opts will be preserved if pcinitrd is executed in ``update'' mode. Another feature of the generated linuxrc is that if the DEBUG variable is set to a non-blank string at the boot prompt, then cardmgr will echo all its status messages to the console, and after linuxrc executes, it will fire up a shell on the console. This can be helpful for debugging initrd problems. However, few commands are available in the normal initrd environment. OPTIONS
-v Verbose mode. Identify files as they are copied. -a, --all Install all socket drivers and block-style PCMCIA device drivers, including memory card, SCSI card, and fixed-disk drivers. This is mainly intended for use by package maintainers. -d alternate-root, --dir=alternate-root Specifies an alternate directory tree to search for all the files used to put together the initrd image. This may be helpful for running pcinitrd after booting from an installation or rescue diskette. -r kernel-release, --release=kernel-release Specifies the kernel release number (i.e., 2.0.28) to use when looking for modules in /lib/modules. The default is the release of the running kernel. -s image-size, --size=image-size Specifies the filesystem size to create on the target file or device, in 1k blocks. The default is 2400. -u, --update Update mode: updates cardmgr and all the kernel modules in an existing initrd image, but does not modify other files. AUTHOR
David Hinds - dahinds@users.sourceforge.net SEE ALSO
pcmcia(5), cardmgr(8), lilo(8). pcmcia-cs $Date PCINITRD(8)
Check Out this Related Man Page
INITRD(4) Linux Programmer's Manual INITRD(4) NAME
initrd - boot loader initialized RAM disk DESCRIPTION
The special file /dev/initrd is a read-only block device. Device /dev/initrd is a RAM disk that is initialized (e.g. loaded) by the boot loader before the kernel is started. The kernel then can use the the block device /dev/initrd's contents for a two phased system boot-up. In the first boot-up phase, the kernel starts up and mounts an initial root file-system from the contents of /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 con- tents. After loading the additional modules, a new root file system (i.e. the normal root file system) is mounted from a different device. BOOT-UP OPERATION When booting up with initrd, the system boots as follows: 1. The boot loader loads the kernel program and /dev/initrd's contents into memory. 2. On kernel startup, the kernel uncompresses and copies the contents of the device /dev/initrd onto device /dev/ram0 and then frees the memory used by /dev/initrd. 3. The kernel then read-write mounts device /dev/ram0 as the initial root file system. 4. If the indicated normal root file system is also the initial root file-system (e.g. /dev/ram0 ) then the kernel skips to the last step for the usual boot sequence. 5. If the executable file /linuxrc is present in the initial root file-system, /linuxrc is executed with uid 0. (The file /linuxrc must have executable permission. The file /linuxrc can be any valid executable, including a shell script.) 6. If /linuxrc is not executed or when /linuxrc terminates, the normal root file system is mounted. (If /linuxrc exits with any file- systems mounted on the initial root file-system, then the behavior of the kernel is UNSPECIFIED. See the NOTES section for the current kernel behavior.) 7. If the normal root file has directory /initrd, device /dev/ram0 is moved from / to /initrd. Otherwise if directory /initrd does not exist device /dev/ram0 is unmounted. (When moved from / to /initrd, /dev/ram0 is not unmounted and therefore processes can remain run- ning from /dev/ram0. If directory /initrd does not exist on the normal root file-system and any processes remain running from /dev/ram0 when /linuxrc exits, the behavior of the kernel is UNSPECIFIED. See the NOTES section for the current kernel behavior.) 8. The usual boot sequence (e.g. invocation of /sbin/init) is performed on the normal root file system. OPTIONS
The following boot loader options when used with initrd, affect the kernel's boot-up operation: initrd=filename Specifies the file to load as the contents of /dev/initrd. For LOADLIN this is a command line option. For LILO you have to use this command in the LILO configuration file /etc/lilo.config. The filename specified with this option will typically be a gzipped file-system image. noinitrd This boot time option disables the two phase boot-up operation. The kernel performs the usual boot sequence as if /dev/initrd was not initialized. With this option, any contents of /dev/initrd loaded into memory by the boot loader contents are preserved. This option permits the contents of /dev/initrd to be any data and need not be limited to a file system image. However, device /dev/ini- trd is read-only and can be read only one time after system startup. root=device-name Specifies the device to be used as the normal root file system. For LOADLIN this is a command line option. For LILO this is a boot time option or can be used as an option line in the LILO configuration file /etc/lilo.config. The device specified by the this option must be a mountable device having a suitable root file-system. CHANGING THE NORMAL ROOT FILE SYSTEM
By default, the kernel's settings (e.g. set in the kernel file with rdev or compiled into the kernel file), or the boot loader option set- ting is used for the normal root file systems. For a NFS-mounted normal root file system, one has to use the nfs_root_name and nfs_root_addrs boot options to give the NFS settings. For more information on NFS-mounted root see the kernel documentation file nfs- root.txt. For more information on setting the root file system also see the LILO and LOADLIN documentation. It is also possible for the /linuxrc executable to change the normal root device. For /linuxrc to change the normal root device, /proc must be mounted. After mounting /proc, /linuxrc changes the normal root device by writing into the proc files /proc/sys/kernel/real-root- dev, /proc/sys/kernel/nfs-root-name, and /proc/sys/kernel/nfs-root-addrs. For a physical root device, the root device is changed by having /linuxrc write the new root file system device number into /proc/sys/kernel/real-root-dev. For a NFS root file system, the root device is changed by having /linuxrc write the NFS setting into files /proc/sys/kernel/nfs-root-name and /proc/sys/kernel/nfs-root-addrs and then writing 0xff (e.g. the pseudo-NFS-device number) into file /proc/sys/kernel/real-root-dev. For example, the following shell command line would change the normal root device to /dev/hdb1: echo 0x365 >/proc/sys/kernel/real-root-dev For a NFS example, the following shell command lines would change the normal root device to the NFS directory /var/nfsroot on a local net- worked NFS server with IP number 193.8.232.7 for a system with IP number 193.8.232.7 and named 'idefix': echo /var/nfsroot >/proc/sys/kernel/nfs-root-name echo 193.8.232.2:193.8.232.7::255.255.255.0:idefix >/proc/sys/kernel/nfs-root-addrs echo 255 >/proc/sys/kernel/real-root-dev USAGE
The main motivation for implementing initrd was to allow for modular kernel configuration at system installation. A possible system installation scenario is as follows: 1. The loader program boots from floppy or other media with a minimal kernel (e.g. support for /dev/ram, /dev/initrd, and the ext2 file- system) and loads /dev/initrd with a gzipped version of the initial file-system. 2. The executable /linuxrc determines what is needed to (1) mount the normal root file-system (i.e. device type, device drivers, file system) 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. 3. The executable /linuxrc loads the necessary modules from the initial root file-system. 4. The executable /linuxrc creates and populates the root file system. (At this stage the normal root file system does not have to be a completed system yet.) 5. The executable /linuxrc sets /proc/sys/kernel/real-root-dev, unmount /proc, the normal root file system and any other file systems it has mounted, and then terminates. 6. The kernel then mounts the normal root file system. 7. Now that the file system is accessible and intact, the boot loader can be installed. 8. The boot loader is configured to load into /dev/initrd a file system with the set of modules that was used to bring up the system. (e.g. Device /dev/ram0 can be modified, then unmounted, and finally, the image is written from /dev/ram0 to a file.) 9. The system is now bootable and additional installation tasks can be performed. The key role of /dev/initrd in the above is to re-use the configuration data during normal system operation without requiring initial ker- nel selection, a large generic kernel or, recompiling the kernel. A second scenario is for installations where Linux runs on systems with different hardware configurations in a single administrative net- work. 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 the /linuxrc file or a file executed by /linuxrc would be different. A third scenario is more convenient recovery disks. Because information like the location of the root file-system partition is not needed at boot time, the system loaded from /dev/initrd can use a dialog and/or auto-detection followed by a possible sanity check. Last but not least, Linux distributions on CD-ROM may use initrd for easy installation from the CD-ROM. The distribution can use LOADLIN to directly load /dev/initrd from CD-ROM without the need of any floppies. The distribution could also use a LILO boot floppy and then bootstrap a bigger ram disk via /dev/initrd from the CD-ROM. CONFIGURATION
The /dev/initrd is a read-only block device assigned major number 1 and minor number 250. Typically /dev/initrd is owned by root.disk with mode 0400 (read access by root only). If the Linux system does not have /dev/initrd already created, it can be created with the following commands: mknod -m 400 /dev/initrd b 1 250 chown root:disk /dev/initrd Also, support for both "RAM disk" and "Initial RAM disk" (e.g. CONFIG_BLK_DEV_RAM=y and CONFIG_BLK_DEV_INITRD=y ) support must be compiled directly into the Linux kernel to use /dev/initrd. When using /dev/initrd, the RAM disk driver cannot be loaded as a module. FILES
/dev/initrd /dev/ram0 /linuxrc /initrd SEE ALSO
chown(1), mknod(1), /dev/ram(4), freeramdisk(8), rdev(8), The documentation file initrd.txt in the kernel source package, the LILO documen- tation, the LOADLIN documentation, the SYSLINUX documentation. NOTES
1. With the current kernel, any file systems that remain mounted when /dev/ram0 is moved from / to /initrd continue to be accessible. How- ever, the /proc/mounts entries are not updated. 2. With the current kernel, if directory /initrd does not exist, then /dev/ram0 will NOT be fully unmounted if /dev/ram0 is used by any process or has any file-system mounted on it. If /dev/ram0 is NOT fully unmounted, then /dev/ram0 will remain in memory. 3. Users of /dev/initrd should not depend on the behavior give in the above notes. The behavior may change in future versions of the Linux kernel. AUTHOR
The kernel code for device initrd was written by Werner Almesberger <almesber@lrc.epfl.ch> and Hans Lermen <lermen@elserv.ffm.fgan.de>. The code for initrd was added to the baseline Linux kernel in development version 1.3.73. Linux 2.0 1997-11-06 INITRD(4)