Usermode Linux with Slackware 9.1 HOWTO

DatuX Usermode Linux with Slackware 9.1 HOWTO
© 2003 http://www.datux.nl/ ? Edwin Eefting edwin@datux.nl

Last updated: 10/05/03

Introduction
This document describes how I installed the latest slackware version (currently 9.1) under UML, without using any prepared bootimages or scripts. There is also a link in this document to a ready-to-run slackware 9.1 installer, and a complete ready-to-run basic 9.1 installation. If there's a new version of slackware, you should be able to create the install image yourself with the help of this document.

Why can't I just install slackware under UML?
UML is something different then programs like VMWare. VMWare provides a complete virtual machine, that comes WITH a bios and thus is able to boot a installation CDROM of any type of operating system. (like a normal computer)

However, UML doesn't provide a virtual machine, i only provides a virtual linux environment, by making users able to start the kernel like a normal program. This means that you can't can ?boot? from a CD-ROM. However, with a little ?fiddeling? (hacking around in the slackware setup scripts) it's still posible to run the slackware setup program under UML. This way you won't need to do the complex stuff to create a root-disk. (according to the UML homepage)

Requirements
Before you can start you first need to comiple a UML-kernel binairy like you normally would do when you want to use UML. Look at http://user-mode-linux.sourceforge.net/ for more info about how to do this.

If you want to install slackware from scratch: The latest .ISO images of slackware. (currently 9.1) At http://www.slackware.org or at http://slackware.datux.nl There is no need to burn them on a CD, you can just use the plain .ISO images with UML.

If you just want a default minimum slackware installation without any hassle just go to http://uml.datux.nl and download the latest UML-image.

Coffee, patience and the ability to think.

The quick and painless way
Download the slackware 9.1 preinstalled image from http://uml.datux.nl , extract it and start UML like this:

psy@phattop:~/uml$ /usr/src/uml-2.4.22/linux ubd1=root_fs ubd2r=/dev/cdrom devfs=nomount root=/dev/ubd11
Checking for the skas3 patch in the host...not found
Checking for /proc/mm...not found
tracing thread pid = 12793
Linux version 2.4.22 (root@phattop) (gcc version 3.2.2) #4 Sun Oct 5 14:13:52 Local time zone must be set--see zic manua
....snip snip....
Tadaaah...you're running a complete virutal linux environment (slackware 9.1) inside of your own Linux enviroment. Nice eh?

If you want to know how it's done read on, otherwise just have fun.

Creating a virtual disk
First we need a virtual disk that we can use as installation target in UML. You could use an existing partion as a target place, but i prefer to use plain files. (because they are easier to copy/move/manage/backup etc..) To create a virtual disk named ?root_fs? type the following command:

psy@phattop:~/uml$ dd if=/dev/zero of=root_fs bs=$((1024*1024)) count=2000
2000+0 records in
2000+0 records out
This will just create a plain empty file of approx. 2gb. This will be the file that we use as our disk and target to install our slackware.

Modifying the original slackware setup disk
Read this chapter if you want to know how to get the slackware installer running under UML or if there is a newer version of slackware you want to use. Otherwise just skip to the next chapter and download a working initrd from http://uml.datux.nl

Getting the original slackware setup-image
We need to get the slackware setup-image that our kernel will use a root filesystem. Normally the installer CDROM is booted from the bios and the root filesystem is automaticly mounted. This image is stored in isolinux/initrd.img. If you use the file command you will see this file is zipped. Copy it to a nice directory and unzip it so that we can work on it. (you need a copy because we will change it!!)

psy@phattop:~/uml$ file /mnt/cdrom/isolinux/initrd.img
/mnt/cdrom/isolinux/initrd.img: gzip compressed data, from Unix, max compression

psy@phattop:~/uml$ cp /mnt/cdrom/isolinux/initrd.img initrd.gz
psy@phattop:~/uml$ gunzip initrd.gz
psy@phattop:~/uml$ file initrd
initrd: Linux rev 1.0 ext2 filesystem data
So now we have a ext2 disk image which contains the root filesystem that is normally used to setup slackware. (it contains the setup program)

Hacking up the slackware setup-image
Lets try to see what happens if we use this initrd setup-image as our root image. Pay attention to how to create the virtual disks:

udb0 will be the installation-image we just unzipped.

udb1 will be the target-image we just created. (root_fs)

udb2 will be our slackware installation CD-ROM (or iso image)

This is what i got:

psy@phattop:~/uml$ /usr/src/uml-2.4.22/linux ubd0=initrd ubd1=root_fs ubd2r=/dev/cdrom devfs=nomount rw
Checking for the skas3 patch in the host...not found
Checking for /proc/mm...not found
tracing thread pid = 8751
Linux version 2.4.22 (root@phattop) (gcc version 3.2.2) #4 Sun Oct 5 14:13:52 Local time zone must be set--see zic manua
On node 0 totalpages: 8192
zone(0): 8192 pages.
zone(1): 0 pages.
zone(2): 0 pages.
Kernel command line: ubd0=initrd ubd1=root_fs ubd2r=/dev/cdrom devfs=nomount rw root=/dev/ubd0
Calibrating delay loop... 2467.25 BogoMIPS
Memory: 28772k available
Dentry cache hash table entries: 4096 (order: 3, 32768 bytes)
Inode cache hash table entries: 2048 (order: 2, 16384 bytes)
Mount cache hash table entries: 512 (order: 0, 4096 bytes)
Buffer cache hash table entries: 1024 (order: 0, 4096 bytes)
Page-cache hash table entries: 8192 (order: 3, 32768 bytes)
Checking for host processor cmov support...Yes
Checking for host processor xmm support...No
Checking that ptrace can change system call numbers...OK
Checking that host ptys support output SIGIO...Yes
Checking that host ptys support SIGIO on close...No, enabling workaround
POSIX conformance testing by UNIFIX
Linux NET4.0 for Linux 2.4
Based upon Swansea University Computer Society NET3.039
Initializing RT netlink socket
Starting kswapd
VFS: Disk quotas vdquot_6.5.1
Journalled Block Device driver loaded
devfs: v1.12c (20020818) Richard Gooch (rgooch@atnf.csiro.au)
devfs: boot_options: 0x0
JFFS version 1.0, (C) 1999, 2000 Axis Communications AB
JFFS2 version 2.1. (C) 2001 Red Hat, Inc., designed by Axis Communications AB.
pty: 256 Unix98 ptys configured
SLIP: version 0.8.4-NET3.019-NEWTTY (dynamic channels, max=256).
RAMDISK driver initialized: 16 RAM disks of 4096K size 1024 blocksize
loop: loaded (max 8 devices)
PPP generic driver version 2.4.2
Universal TUN/TAP device driver 1.5 (C)1999-2002 Maxim Krasnyansky
SCSI subsystem driver Revision: 1.00
scsi0 : scsi_debug, Version: 0.61 (20020815), num_devs=1, dev_size_mb=8, opts=0x0
Vendor: Linux Model: scsi_debug Rev: 0004
Type: Direct-Access ANSI SCSI revision: 03
blkmtd: error: missing `device' name

Initializing software serial port version 1
mconsole (version 2) initialized on /home/psy/.uml/cJnBNr/mconsole
Partition check:
ubda: unknown partition table
ubdb: unknown partition table
ubdc: unknown partition table
UML Audio Relay (host dsp = /dev/sound/dsp, host mixer = /dev/sound/mixer)
Initializing stdio console driver
NET4: Linux TCP/IP 1.0 for NET4.0
IP Protocols: ICMP, UDP, TCP
IP: routing cache hash table of 512 buckets, 4Kbytes
TCP: Hash tables configured (established 2048 bind 4096)
NET4: Unix domain sockets 1.0/SMP for Linux NET4.0.
EXT2-fs warning: mounting unchecked fs, running e2fsck is recommended
VFS: Mounted root (ext2 filesystem).
init started: BusyBox v0.60.5 (2003.02.16-05:06+0000) multi-call binary
proc on /proc type proc (rw)



If you are not using a US keyboard, you may now load a different
keyboard map. To select a different keyboard map, please enter 1
now. To continue using the US map, just hit enter.

Enter 1 to select a keyboard map:
.......etc...




This seems to be ok, however pay attention to the partition check. We don't seem to have a hda, hdb, hdc like we normally do. To be able to access the devices we have to create some new devices in the /dev directory:

root@slackware:/# cd /dev
root@slackware:/dev# rm hda hdb hdc
root@slackware:/dev# mknod hda b 98 0
root@slackware:/dev# mknod hda1 b 98 1
root@slackware:/dev# mknod hda2 b 98 2
root@slackware:/dev# mknod hdb b 98 16
root@slackware:/dev# mknod hdb1 b 98 17
root@slackware:/dev# mknod hdb2 b 98 18
root@slackware:/dev# mknod hdc b 98 32
root@slackware:/dev# mknod hdc1 b 98 33
root@slackware:/dev# mknod hdc2 b 98 34
The virtual disks have a major number of 98, and a minor number of 0 for the first disk, 16 for the second..etc.. We also will disable the makedevs script because it's not needed and it takes ages to run under UML:

root@slackware:/dev# mv makedevs.sh makedevs.sh.old
root@slackware:/dev# touch makedevs.sh
root@slackware:/dev# chmod 555 makedevs.sh
Now lets try to run fdisk to see if we can partition our virtual disk:

root@slackware:/dev# cfdisk /dev/hdb
.......partition your disks if it works.....
It worked for me, if it doesn't for you then you didn't assign udb1 to your root_fs file.

Now we can try to run setup and install slackware. However, you will notice that it won't detect the partitions and it will complain. This is because there is a /sbin/probe script that is used to detect the partitions. It uses /proc/partition to detect these, however the names and numers in these files are all different because we run UML. I would go into detail here, so lets just hack up the probe script to make it working again:

If you would run the /sbin/probe command right now it will take sometime and it will come up with no disks. Edit /sbin/probe and make the following changes. You can use vi in UML, but it sucks because of the terminal settings or something, so just halt the system by typing halt and mount/edit the initrd file manually. Don't kill UML, because it could corrupt your initrd image which is ext2. (no journalling):

root@slackware:/dev# halt
root@slackware:/dev#
The system is going down NOW !!
Sending SIGTERM to all processes.
Oct 5 17:47:50 slackware syslog.info System log daemon exiting.
Sending SIGKILL to all processes.
The system is halted. Press Reset or turn off power
System halted.

psy@phattop:~/uml$ su
Password:
root@phattop:/home/psy/uml# mount -o loop initrd /mnt/hd
root@phattop:/home/psy/uml# mcedit /mnt/hd/sbin/probe
...editing..(yeah i'm lame ;)...
Find these lines (search for hda):

if [ "$MAJOR" = "3" ]; then
list_ide $MAJOR $MINOR hda hdb
And change it to:

if [ "$MAJOR" = "98" ]; then
list_ide $MAJOR $MINOR hda
list_ide $MAJOR $MINOR hdb
list_ide $MAJOR $MINOR hdc
All the things we do are called ?hacks? because they are very ugly and ?disrupt? the normal operation slackware setup scripts. It will only work in this particular UML situation. (with these virtual drive assignments)

Now unmount the image (very important because we get corruption if we mount an image multiple times at once!) and boot UML linux again. Lets try if the probe script works better now:

root@phattop:/home/psy/uml# mcedit -d /mnt/hd/sbin/probe
...exit your editor...
root@phattop:/home/psy/uml# umount /mnt/hd
root@phattop:/home/psy/uml# exit
exit

psy@phattop:~/uml$ /usr/src/uml-2.4.22/linux ubd0=initrd ubd1=root_fs ubd2r=/dev/cdrom devfs=nomount rw
Checking for the skas3 patch in the host...not found
Checking for /proc/mm...not found
tracing thread pid = 12793
Linux version 2.4.22 (root@phattop) (gcc version 3.2.2) #4 Sun Oct 5 14:13:52 Local time zone must be set--see zic manua
....snip snip....

root@slackware:/# probe
Disk /dev/hda doesn't contain a valid partition table
Disk /dev/hdc doesn't contain a valid partition table

Disk /dev/hda: 6 MB, 6619136 bytes
128 heads, 32 sectors/track, 3 cylinders
Units = cylinders of 4096 * 512 = 2097152 bytes


Disk /dev/hdb: 2097 MB, 2097152000 bytes
128 heads, 32 sectors/track, 1000 cylinders
Units = cylinders of 4096 * 512 = 2097152 bytes

Device Boot Start End Blocks Id System
/dev/hdb1 1 1000 2047984 83 Linux

Disk /dev/hdc: 655 MB, 655593472 bytes
128 heads, 32 sectors/track, 312 cylinders
Units = cylinders of 4096 * 512 = 2097152 bytes

root@slackware:/# setup
...setup running and working...
Well it seems to work! We're even able to run setup and choose our target partition. (don't mind the errors ;) Now you seem to have a working initrd for uml!! Just halt the system again and run a fsck.ext2 initrd to see if there's no corruption. In the future you can always use this image to reinstall slackware. (offcourse you can download it at http://uml.datux.nl)

Continue with the next chapter to see how to install slackware using the image.

Installing slackware
To do this you need a modified version of initrd, like we just created in the previous chapter. Download it from http://uml.datux.nl

Running the modified slackware installer
Make sure you have the modified initrd and you have created the root_fs file. Run UML with the following parameters to start installing:

psy@phattop:~/uml$ /usr/src/uml-2.4.22/linux ubd0=initrd ubd1=root_fs ubd2r=/dev/cdrom devfs=nomount rw
Checking for the skas3 patch in the host...not found
Checking for /proc/mm...not found
tracing thread pid = 12793
Linux version 2.4.22 (root@phattop) (gcc version 3.2.2) #4 Sun Oct 5 14:13:52 Local time zone must be set--see zic manua
....snip snip....

root@slackware:/# setup
...setup running...
Just run cfdisk like you normally do. /dev/hdb will be your root disk that you'll have to partition using cfdisk: cfdisk /dev/hdb. You probably want to use the following settings in setup:

I recommend you don't assign any swapspace, since it's more efficient to let the host do the swapping. Just use the paramter mem=512M for example.

Don't install a kernel image (since we already use one)

Don't install LILO. (we don't BOOT, we just run the UML-kernel)

Don't let setup create bootflop (duh)

Don't use hotplug support. (all devices are virtual anyway)

Make the virtual disks accessible
After you're done with setup you have to make some changes to your /dev directory before you'll be able to boot your freshly installed slackware version:

root@slackware:/# cd /dev
root@slackware:/dev# rm hda hdb hdc
root@slackware:/dev# mknod hda b 98 0
root@slackware:/dev# mknod hda1 b 98 1
root@slackware:/dev# mknod hda2 b 98 2
root@slackware:/dev# mknod hdb b 98 16
root@slackware:/dev# mknod hdb1 b 98 17
root@slackware:/dev# mknod hdb2 b 98 18
root@slackware:/dev# mknod hdc b 98 32
root@slackware:/dev# mknod hdc1 b 98 33
root@slackware:/dev# mknod hdc2 b 98 34
(You probably can do it the easy way and just copy hd* from the /dev directory that already is on the installation image.)

This is neccesary because the major/minor numbers of your virtual disk are different than that of a typical ide-device. This is just a quick hack, you also can create devices like /dev/udb0 or just devfs.

After this you're done installing and you could make a backup of your root_fs and perhaps rename it to slackware-9.1.

Now you're ready to run your slackware installation. (see next chapter) When you're this far you only need to cleanup some things. The modules that are used are standard slackware 9.1 kernel modules. You need to use your own modules offcourse, but it's easier to compile everything into the kernel when using UML, and disable module loading all together.

I also noticed that /sbin/fsck.reiserfs should be linked to /sbin/reiserfsck. (in order for the system to be able to have your reiser filesystem checked upon startup. Use shutdown -F)

Running the installed image
When you're done installing slackware, or when you've downloaded a preinstalled image from http://uml.datux.nl you can run slackware like this:

psy@phattop:~/uml$ /usr/src/uml-2.4.22/linux ubd1=root_fs ubd2r=/dev/cdrom devfs=nomount root=/dev/ubd11
Checking for the skas3 patch in the host...not found
Checking for /proc/mm...not found
tracing thread pid = 12793
Linux version 2.4.22 (root@phattop) (gcc version 3.2.2) #4 Sun Oct 5 14:13:52 Local time zone must be set--see zic manua
....snip snip....
Tadaaah...you're running a complete virtual linux environment (slackware 9.1) inside of your own Linux enviroment. Nice eh?

Our own findings and tips
We use UML mostly for development and testing. There is kind of a performance penalty when you run programs under UML. This is especially is notable when running the slackware installation procedure. However, you probably have to do this only once and after that you can use your images over and over again.

To get better performance you should apply the SKAS patch. I used an older patch on my 2.4.22 kernel but it worked without any problems.

I also recommend to have a look at the COW system for your virtual disk images. This way you can safe diskspace and you'll have better performance when you run multiple UML's at once.

Install the uml_utilities as well, otherwise you won't be able to access your terminals when you run slackware. UML starts a xterm for every virtual terminal.

Good luck!

Edwin Eefting

edwin@datux.nl

Link Original: http://uml.datux.nl/UML-Slackware-HOWTO.html

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