Previous Next Contents

3. The aboot Loader

When using the SRM firmware, aboot is the preferred way of booting Linux. It supports:

3.1 Getting and Building aboot

The latest sources for aboot are available in this ftp directory. The description in this manual applies to aboot version 0.5 or newer.

Once you downloaded and extracted the latest tar file, take a look at the README and INSTALL files for installation hints. In particular, be sure to adjust the variables in Makefile and in include/config.h to match your environment. Normally, you won't need to change anything when building under Linux, but it is always a good idea to double check. If you're satisfied with the configuration, simply type make to build it (if you're not building under Linux, be advised that aboot requires GNU make).

After running make, the aboot directory should contain the following files:


This is the actual aboot executable (either an ECOFF or ELF object file).


Same as above, but it contains only the text, data and bss segments---that is, this file is not an object file.


Utility to install aboot on a hard disk.


Utility to install aboot on an ext2 filesystem (usually used for floppies only).


Utility to install aboot on a iso9660 filesystem (used by CD-ROM distributors).


Utility to configure an installed aboot.

3.2 Floppy Installation

The bootloader can be installed on a floppy using the e2writeboot command (note: this can't be done on a Jensen since its firmware does not support booting from floppy). This command requires that the disk is not overly fragmented as it needs to find enough contiguous file blocks to store the entire aboot image (currently about 90KB). If e2writeboot fails because of this, reformat the floppy and try again (e.g., with fdformat(1)). For example, the following steps install aboot on floppy disk assuming the floppy is in drive /dev/fd0:

fdformat /dev/fd0
mke2fs /dev/fd0
e2writeboot /dev/fd0 bootlx

3.3 Harddisk Installation

Since the e2writeboot command may fail on highly fragmented disks and since reformatting a harddisk is not without pain, it is generally safer to install aboot on a harddisk using the swriteboot command. swriteboot requires that the first few sectors are reserved for booting purposes. We suggest that the disk be partitioned such that the first partition starts at an offset of 2048 sectors. This leaves 1MB of space for storing aboot. On a properly partitioned disk, it is then possible to install aboot as follows (assuming the disk is /dev/sda):

swriteboot /dev/sda bootlx

On a Jensen, you will want to leave some more space, since you need to write a kernel to this place, too---2MB should be sufficient when using compressed kernels. Use swriteboot as described in Section booting to write bootlx together with the Linux kernel.

3.4 CD-ROM Installation

To make a CD-ROM bootable by SRM, simply build aboot as described above. Then, make sure that the bootlx file is present on the iso9660 filesystem (e.g., copy bootlx to the directory that is the filesystem master, then run mkisofs on that directory). After that, all that remains to be done is to mark the filesystem as SRM bootable. This is achieved with a command of the form:

isomarkboot filesystem bootlx

The command above assumes that filesystem is a file containing the iso9660 filesystem and that bootlx has been copied into the root directory of that filesystem. That's it!

3.5 Building the Linux Kernel

A bootable Linux kernel can be built with the following steps. During the make config, be sure to answer "yes" to the question whether you want to boot the kernel via SRM.

cd /usr/src/linux
make config
make dep
make boot

The last command will build the file arch/alpha/boot/vmlinux.gz which can then be copied to the disk from which you want to boot from. In our floppy disk example above, this would entail:

mount /dev/fd0 /mnt
cp arch/alpha/boot/vmlinux.gz /mnt
umount /mnt

3.6 Booting Linux

With the SRM firmware and aboot installed, Linux is generally booted with a command of the form:

boot devicename -fi filename -fl flags

The filename and flags arguments are optional. If they are not specified, SRM uses the default values stored in environment variables BOOT_OSFILE and BOOT_OSFLAGS. The syntax and meaning of these two arguments is described in more detail below.

Boot Filename

The filename argument takes the form:


n is a single digit in the range 1..8 that gives the partition number from which to boot from. filename is the path of the file you want boot. For example to boot from the second partition of SCSI device 6, you would enter:

boot dka600 -file 2/vmlinux.gz

Or to boot from floppy drive 0, you'd enter:

boot dva0 -file vmlinux.gz

If a disk has no partition table , aboot pretends the disk contains one ext2 partition starting at the first diskblock. This allows booting from floppy disks.

As a special case, partition number 0 is used to request booting from a disk that does not (yet) contain a file system. When specifying "partition" number 0, aboot assumes that the Linux kernel is stored right behind the aboot image. Such a layout can be achieved with the swriteboot command. For example, to setup a filesystem-less boot from /dev/sda, one could use the command:

swriteboot /dev/sda bootlx vmlinux.gz

Booting a system in this way is not normally necessary. The reason this feature exists is to make it possible to get Linux installed on a systems that can't boot from a floppy disk (e.g., the Jensen).

Boot Flags

A number of bootflags can be specified. The syntax is:

-flags "options..."

Where "options..." is any combination the following options (separated by blanks). There are many more bootoptions, depending on what drivers your kernel has installed. The options listed below are therefore just examples to illustrate the general idea:


Copy root file system from a (floppy) disk to the RAM disk before starting the system. The RAM disk will be used in lieu of the root device. This is useful to bootstrap Linux on a system with only one floppy drive.


Sets floppy configuration to str.


Select device dev as the root-file system. The device can be specified as a major/minor hex number (e.g., 0x802 for /dev/sda2) or one of a few canonical names (e.g., /dev/fd0, /dev/sda2).


Boot system in single user mode.


Enable kernel-gdb (works only if CONFIG_KGDB is enabled; a second Alpha system needs to be connected over the serial port in order to make this work)

Some SRM implementations (e.g., the one for the Jensen) are handicapped and allow only short option strings (e.g., at most 8 characters). In such a case, aboot can be booted with the single-character boot flag "i". With this flag, aboot will prompt the user to interacively enter a boot option string of up to 256 characters. For example:

boot dka0 -fl i
aboot> 3/vmlinux.gz root=/dev/sda3 single

Since booting in that manner quickly becomes tedious, aboot allows to define short-hands for frequently used commandlines. In particular, a single digit option (0-9) requests that aboot uses the corresponding option string stored in file /etc/aboot.conf. A sample aboot.conf is shown below:

# aboot default configurations
0:3/vmlinux.gz root=/dev/sda3
1:3/vmlinux.gz root=/dev/sda3 single
2:3/ root=/dev/sda3
3:3/vmlinux root=/dev/sda3
8:- root=/dev/sda3            # fs-less boot of raw kernel
9:0/vmlinux.gz root=/dev/sda3 # fs-less boot of (compressed) ECOFF kernel

With this configuration file, the command

boot dka0 -fl 1

corresponds exactly to the boot command shown above. It is quite easy to forget what number corresponds to what option string. To alleviate this problem, boot with option "h" and aboot will print the contents of /etc/aboot.conf before issueing the prompt for the full option string.

Finally, whenever aboot prompts for an option string, it is possible to enter one of the single character flags ("i", "h", or "0"-"9") to get the same effect as if that flag had been specified in the boot command line. For example, you could boot with flag "i" and then type "h" (followed by return) to remind yourself of the contents of /etc/aboot.conf

Selecting the Partition of /etc/aboot.conf

When installed on a harddisk, aboot needs to know what partition to search for the /etc/aboot.conf file. A newly compiled aboot will search the second partition (e.g., /dev/sda2). Since it would be inconvenient to have to recompile aboot just to change the partition number, abootconf allows to directly modify an installed aboot. Specifically, if you want to change aboot to use the third partition on disk /dev/sda, you'd use the command:

abootconf /dev/sda 3

You can verify the current setting by simply omitting the partition number. That is: abootconf /dev/sda will print the currently selected partition number. Note that aboot does have to be installed already for this command to succeed. Also, when installing a new aboot, the partition number will fall back to the default (i.e., it will be necessary to rerun abootconf).

Since aboot version 0.5, it is also possible to select the aboot.conf partition via the boot command line. This can be done with a command line of the form a:b where a is the partition that holds /etc/aboot.conf and b is a single-letter option as described above (0-9, i, or h). For example, if you type boot -fl "3:h" dka100 the system boots from SCSI ID 1, loads /etc/aboot.conf from the third partition, prints its contents on the screen and waits for you to enter the boot options.

3.7 Booting Over the Network

Two prelimenary steps are necessary before Linux can be booted via a network. First, you need to set the SRM environment variables to enable booting via the bootp protocol and second you need to setup another machine as the your boot server. Please refer to the SRM documentation that came with your machine for information on how to enable bootp. Setting up the boot server is obviously dependent on what operating system that machine is running, but typically it involves starting the program bootpd in the background after configuring the /etc/bootptab file. The bootptab file has one entry describing each client that is allowed to boot from the server. For example, if you want to boot the machine, then an entry of the following form would be needed:\

This entry assumes that the machine's Ethernet address is 08012B1C51F8 and that its IP address is The Ethernet address can be found with the show device command of the SRM console or, if Linux is running, with the ifconfig command. The entry also defines that if the client does not specify otherwise, the file that will be booted is vmlinux.bootp in directory /remote. For more information on configuring bootpd, please refer to its man page.

Next, build aboot with with the command make netboot. Make sure the kernel that you want to boot has been built already. By default, the aboot Makefile uses the kernel in /usr/src/linux/arch/alpha/boot/vmlinux.gz (edit the Makefile if you want to use a different path). The result of make netboot is a file called vmlinux.bootp which contains aboot and the Linux kernel, ready for network booting.

Finally, copy vmlinux.bootp to the bootsever's directory. In the example above, you'd copy it into /remote/vmlinux.bootp. Next, power up the client machine and boot it, specifying the Ethernet adapter as the boot device. Typically, SRM calls the first Ethernet adapter ewa0, so to boot from that device, you'd use the command:

boot ewa0

The -fi and -fl options can be used as usual. In particular, you can ask aboot to prompt for Linux kernel arguments by specifying the option -fl i.

Previous Next Contents