lsscsi

Many people imagine that SCSI drives are obsolete, but, in fact, both hard drives and solid state drives, as well as DVD drives, continue to use SCSI, although in a highly modified standard. For help, lsscsi has an info file, but not a man file. Adding --list (-L), --long (-l), and --verbose (-v) to the command all give more information, while --classic (-c) is the equivalent of:

cat /proc/scsi/scsi

If you want the names of devices, add --generic (g) (Figure 7).

Figure 7: As lssci shows, SCSI devices continue to be a standard part of modern computer systems.

dmesg

dmesg reads the kernel ring buffer where messages about a system's startup messages are stored, including information about the initialization of device drivers or kernel modules. Although the results can often be hit or miss, dmesg is sometimes an ideal place to start troubleshooting. With the bare command, you can scroll through startup messages, but in most cases, it is more efficient to search instead. For instance, to find messages about USB devices, enter:

dmesg | grep -i usb | less

in which the -i option ignores letter cases. Note that dmesg must be run as root. As an alternative to dmesg, you can read the file /var/log/dmesg in a text editor (Figure 8).

Figure 8: Read messages in the kernel ring buffer with dmesg. Combined with grep, it can show useful information.

/proc

The pseudo filesystem /proc contains information from the kernel. It contains one subdirectory for each process. The names of the subdirectories are usually self-explanatory, such as cpu, cwd (current working directory), environ, and so on. You can view detailed information using a text viewer such as cat or less, or sysctl to read the contents, but be careful not to edit in case you crash the system (Figure 9).

Figure 9: Search the /proc pseudo filesystem for information when troubleshooting.