Mastering lsscsi: Understand SCSI, Install, Options, and Debugging

What is SCSI?

SCSI (Small Computer System Interface) is a comprehensive data‑transfer protocol that enables hosts to send commands, receive status, and exchange block data with storage devices such as disks, tapes, optical drives, and printers. It typically resides in device drivers or host‑adapter firmware.

Common Disk Interfaces

IDE

IDE (Integrated Drive Electronics) integrates the drive controller with the disk platter. Historically referred to ATA‑1, it has been superseded by newer standards such as ATA, Ultra ATA, DMA, and Ultra DMA. IDE is inexpensive and compatible but offers slower data transfer and no hot‑plug support.

SCSI

SCSI is a high‑speed data‑transfer technology originally designed for minicomputers. It supports multiple devices, multitasking, large bandwidth, low CPU usage, and hot‑plug capability, making it common in mid‑ to high‑end servers and workstations despite its higher cost.

SATA

SATA (Serial Advanced Technology Attachment) is the modern serial interface for disks. It uses an embedded clock, provides stronger error‑correction, and can verify command integrity. SATA also offers a simple structure and hot‑plug support.

lsscsi Command

Installation

# Debian/Ubuntu
apt-get install lsscsi
# Alpine
apk add lsscsi
# Arch Linux
pacman -S lsscsi
# CentOS
yum install lsscsi
# Fedora
dnf install lsscsi
# Docker (run container)
docker run cmd.cat/lsscsi lsscsi

Manual and Options

The command lists SCSI/SATA devices such as hard‑disk and optical‑drive units. Its syntax is: lsscsi [options] [H:C:T:L] Key options include:

-g : show generic SCSI device file name

-k : display kernel name instead of device node name

-d : show major/minor numbers of the device node

-H : list SCSI hosts rather than devices

-l : display additional per‑device information

-c : output equivalent to cat /proc/scsi/scsi -p : show data‑integrity (DIF/DIX) protection info

-t : display transport information (ATA, FC, SAS, etc.)

-L : present extra attributes as key=value -v : output the directory name when information is found

-y<path> : assume sysfs is mounted at the given path

-s : show human‑readable capacity

-x : display LUN number in hexadecimal

-P : output valid protection mode information

-i : show udev‑related attributes

-w : display WWN (World Wide Name)

Examples

List all SCSI devices:

peng@ubuntu:~$ lsscsi
[3:0:0:0]    cd/dvd  NECVMWar VMware SATA CD01 1.00  /dev/sr0
[32:0:0:0]   disk    VMware, VMware Virtual S 1.0   /dev/sda

Show detailed attributes with -L:

peng@ubuntu:~$ lsscsi -L
[3:0:0:0]    cd/dvd  ... /dev/sr0
  device_blocked=0
  iocounterbits=32
  ...
[32:0:0:0]   disk    ... /dev/sda
  device_blocked=0
  iocounterbits=32
  queue_depth=32
  ...

Show human‑readable capacity with -s:

peng@ubuntu:~$ lsscsi -s
[3:0:0:0]    cd/dvd  ... /dev/sr0        -
[32:0:0:0]   disk    ... /dev/sda        536GB

Related SCSI File Nodes

Key locations in the Linux filesystem:

/proc/scsi/ – contains device_info, mptspi, scsi, sg directories.

/sys/class/scsi_host – lists host adapters (host0, host1, …).

/sys/class/scsi_device – shows devices by H:C:T:L identifiers.

/sys/class/scsi_disk – disk‑specific entries.

/sys/class/scsi_generic – generic SCSI device nodes (sg0, sg1, …).

/sys/bus/scsi – contains drivers and device trees.

Example of reading /proc/scsi/scsi:

Attached devices:
Host: scsi32 Channel: 00 Id: 00 Lun: 00
  Vendor: VMware, Model: VMware Virtual S Rev: 1.0
  Type:   Direct-Access   ANSI  SCSI revision: 02
Host: scsi3 Channel: 00 Id: 00 Lun: 00
  Vendor: NECVMWar Model: VMware SATA CD01 Rev: 1.00
  Type:   CD-ROM          ANSI  SCSI revision: 05

Enabling SCSI Logging for Debugging

To compile the kernel with SCSI logging support, enable CONFIG_SCSI_LOGGING in the kernel configuration. After boot, logging can be turned on via the /proc/sys/dev/scsi/logging_level interface.

Set the logging level (bitmask) to enable specific log types, for example:

# echo 0 > /proc/sys/dev/scsi/logging_level   # disable all SCSI logs
# echo -1 > /proc/sys/dev/scsi/logging_level  # enable all SCSI logs (send to syslog)

The scsi_logging_level variable is a 32‑bit integer where each 3‑bit field represents a different logging category (error, ioctl, etc.). Adjust the bitmask according to the desired verbosity.