The Linux 2.4 SCSI subsystem HOWTO
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# 8.3. proc interface

To display the SCSI devices currently attached (and recognized) by the SCSI subsystem use cat /proc/scsi/scsi.

The output looks like this:

        Attached devices:
        Host: scsi0 Channel: 00 Id: 02 Lun: 00
          Vendor: PIONEER  Model: DVD-ROM DVD-303  Rev: 1.10
          Type:   CD-ROM              ANSI SCSI revision: 02
        Host: scsi1 Channel: 00 Id: 00 Lun: 00
          Vendor: IBM      Model: DNES-309170W     Rev: SA30
          Type:   Direct-Access       ANSI SCSI revision: 03

After the "Attached devices:" line there are 3 lines for each recognized device. The first of these lines is SCSI address information discussed in Section 3.1. The following 2 lines of data are obtained from a INQUIRY command that was performed on the device when it was attached. See Section 9.4 for the relationship between the ordering of these devices compared with the sg driver's ordering (which most of the time is the same).

Existing devices can be removed using echo "scsi remove-single-device <h> <b> <t> <l>" > /proc/scsi/scsi where the variables are host, bus (channel), target (scsi id) and lun. The success (or otherwise) of this command can be determined by sending a subsequent cat /proc/scsi/scsi command. The removal will fail if the device is busy (e.g. if a file system on the device is mounted).

New devices can be added using echo "scsi add-single-device <h> <b> <t> <l>" > /proc/scsi/scsi where the variables are host, bus (channel), target (scsi id) and lun. The success (or otherwise) of this command can be determined by sending a subsequent cat /proc/scsi/scsi command. [1]

The SCSI subsystem does not support hot-plugging of SCSI devices (there may also be electrical issues on the associated SCSI parallel bus). It is recommended that those who use add+remove-single-device make sure that other devices on that SCSI bus are inactive if re-plugging is going to take place.

To output a list of internal SCSI command blocks use echo "scsi dump <n>" > /proc/scsi/scsi where the numeric value of <n> doesn't matter. This is probably only of interest to people chasing down bugs within the SCSI subsystem.

To start (or stop) logging information being sent to the console/log use echo "scsi log <token> <n>" > /proc/scsi/scsi where <token> is one of: {all, none, error, timeout, scan, mlqueue, mlcomplete, llqueue, llcomplete, hlqueue, hlcomplete, ioctl} and <n> is a number between 0 and 7. The tokens "all" and "none" don't take an <n> argument. Prefix meanings:

        hl    upper level drivers [exception: sg uses "timeout"]
        ml    mid level
        ll    lower level drivers
               [adapter drivers often have there own flags]

The value "0" turns off logging while "7" maximizes the volume of output. Logging information will only be output if CONFIG_SCSI_LOGGING was selected in the kernel build.

| Warning: "scsi log all" (and several other variants) can cause a logging infinite loop if the log file (typically `/var/log/messages` ) lies on a SCSI disk. Either turn off the kernel logging daemon or direct its output to a non SCSI device.

### Notes

[1] | The parsing of "add-single-device" and "remove-single-device" is rather inflexible. Hence it is best to stay close to the demonstrated syntax with no extra spaces (and no tabs).

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