8.1. boot parameters

SCSI drivers that are built into the kernel are checked in a pre-determined order to see if HBAs that they can control are present. The user has no control over this order which in most cases is arbitrary but in the case of some older ISA adapters is required to stop misidentification [1] .

scsi_logging=<n> where <n> is 0 to turn logging off where <n> is non-zero to turn logging on max_scsi_luns=<n> where <n> is a number between 1 and 8 scsihosts=host0:hosts1::host3

The recently introduced devfs defines a "scsihosts" boot time parameter to give the user some control over this. See the devfs documentation [ref: W5] for a description. The host names given in the list to the "scsihosts" boot option are the names of lower level drivers (e.g. "scsihosts=advansys:imm::ide-scsi"). Devfs does not need to be present for "scsihosts" to be used. The "scsihosts" parameter, if given, is echoed during in the boot up messages. For example:

scsi: host order: advansys:imm::ide-scsi

Also if multiple HBA are present in a system then they are scanned in a fixed order (see footnote). The "scsihosts" parameter only effects how these HBAs are indexed (i.e. which SCSI adapter numbers are associated with them by the kernel). In the above example, if the "imm" driver is not found during boot up, then the scsi adapter number "1" is not allocated. If the "imm" driver is later loaded as a module, then it will adopt scsi adapter number "1". If a driver that is not named in "scsihosts" is found, then it will get the next available scsi adapter number (e.g. a built in aic7xxx driver would get scsi adapter number "2" in the above example).

A full list of kernel parameters with some explanations can be found in the file /usr/src/linux/Documentation/kernel-parameters.txt.