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Title: LILO : The "linear" option

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LILO : The "linear" option

Symptom:

LILO can't find the boot kernels when booting from the harddrive and stops at LI (or another incomplete part of the word LILO, see also LILO fails: Error-messages and their interpretation (kgw_lilo_errmsg.html)). This happens even though you have respected the 1024 cylinder limit (Linux above 1024 cylinders and LILO(1024_Zylinder.html)))

This happens in particular, if you have installed another operating system in the beginning of your harddrive (e.g. Windows NT).

Cause:

One possible cause : LILO was installed with the option "linear" enabled.

Solution:

Deactivate the option "linear" in /etc/lilo.conf by erasing it or by putting a comment sign in front of that line :

# linear
Reinstall lilo: as root, invoke the command
#  /sbin/lilo

Background :

Effect of the "linear" option : All references (pointers) to harddrive sectors of /boot/boot.b, /boot/map, kernel, etc. are stored in the LILO bootsector and in /boot/map as logical sector adresses instead of physical (cylinder-head-sector) adresses.

At boot time the LILO boot sector determines the geometry of the harddrive by calling a BIOS function. It then converts the logical sector adresses back to physical adresses. The real access to the harddrive(s) is done using the physical sector adresses.

Purpose : The "linear" option is useful when the BIOS "sees" a particular harddrive with a geometry different from the one Linux uses. The logical sector adresses remain correct independent of the geometry of the harddrive.

This is a rare case, so the "linear" option isn't really necessary most of the time. It is nevertheless activated by default in all cases when LILO was installed with YaST (in S.u.S.E. Linux until version 5.2).

Difficulty : When using the "linear" option another limitation (so far undocumented) must be taken into account (besides the 1024 cylinder limitation). It comes into effect in particular for modern big harddrives : "linear" only works

   with 16 sectors/track     below 512 MB
   with 32 sectors/track     below   1 GB
   with 63 sectors/track     below  ~2 GB
This limitation is more restrictive than the 1024 cylinder limitation when there are more than 64 heads. Nowadays, geometries with 128 or 255 heads are very common.

The reason : One of the auxiliary results during the conversion into physical adresses at boot time is the track of the particular sector and this conversion is done with 16 bit arithmetics. Thus track must be < 65536 .

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See also:

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Keywords: BOOT, BOOT PROBLEMS, LILO, LINEAR, 1024, CYLINDER, INSTALLATION

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Categories: LILO

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Feedback welcome: Send Mail to Klaus.Wagner@suse.de (Please give the following subject: SDB-kgw_lilo_linear)

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SDB-kgw_lilo_linear, Copyright SuSE GmbH, Nuremberg, Germany - Version: 21. Apr 1998
Impressum - Last generated: 24. Feb 1999 14:56:54 by maddin with sdb_gen 1.00.0