davetang / learning_linux

Linux notes

Learning linux

I recently purchased the Linux Humble Bundle for around 40 USD. I'll slowly go through the books and will consolidate all my notes here.

Useful commands

List SCSI devices (typically hard disks); useful for listing block devices. Note that this is not limited to SCSI devices and block devices connected via USB will also be listed. Output from the examples below are from two separate computers.

You may need to install it first.

# Debian/Ubuntu
sudo apt install -y lsscsi

# CentOS/RHEL
yum install lsscsi

List SCSI devices (or hosts) and list NVMe devices (version 0.30 and higher).

sudo lsscsi

[0:0:0:0]    disk    ATA      SUNEAST SE800 SS AA20  /dev/sda

Lists NVMe controllers and SCSI hosts.

sudo lsscsi --controllers

[0]    ahci
[1]    ahci
[2]    ahci
[3]    ahci

On a computer that has a NVMe controller.

sudo lsscsi --long

[2:0:0:0]    disk    ATA      TOSHIBA DT01ACA2 AC60  /dev/sda
  state=running queue_depth=32 scsi_level=6 type=0 device_blocked=0 timeout=30
[3:0:0:0]    disk    ATA      WDC  WDS100T2B0A 40WD  /dev/sdb
  state=running queue_depth=32 scsi_level=6 type=0 device_blocked=0 timeout=30
[N:0:4:1]    disk    SAMSUNG MZVLB512HAJQ-000H1__1              /dev/nvme0n1
  capability=0  ext_range=256  hidden=0  nsid=1  range=0  removable=0

smartctl - Control and Monitor Utility for SMART Disks

Install if necessary.

sudo apt install -y smartmontools

Scan for devices.

sudo smartctl --scan

/dev/sda -d scsi # /dev/sda, SCSI device
/dev/sdb -d scsi # /dev/sdb, SCSI device
/dev/nvme0 -d nvme # /dev/nvme0, NVMe device

Info on /dev/sda.

sudo smartctl --info /dev/sda

smartctl 7.3 2022-02-28 r5338 [x86_64-linux-6.1.0-18-amd64] (local build)
Copyright (C) 2002-22, Bruce Allen, Christian Franke, www.smartmontools.org

=== START OF INFORMATION SECTION ===
Device Model:     SUNEAST SE800 SSD 1T
Serial Number:    30091897265
LU WWN Device Id: 5 000000 000002f9f
Firmware Version: 030fAA20
User Capacity:    1,024,209,543,168 bytes [1.02 TB]
Sector Size:      512 bytes logical/physical
Rotation Rate:    Solid State Device
Form Factor:      2.5 inches
TRIM Command:     Available, deterministic, zeroed
Device is:        Not in smartctl database 7.3/5319
ATA Version is:   ACS-4 (minor revision not indicated)
SATA Version is:  SATA 3.2, 6.0 Gb/s (current: 6.0 Gb/s)
Local Time is:    Tue Mar 26 23:31:18 2024 JST
SMART support is: Available - device has SMART capability.
SMART support is: Enabled

View system's partition table; useful for finding out the File system, device name, start/end sectors.

sudo parted -l

Locate and print block device attributes; useful for for getting information on a device's file system and UUID.

sudo blkid

Use udevadm to show the path and attributes of a device.

sudo udevadm info --query=all --name=/dev/sdb

Run cat /proc/devices to see the block and character devices for which your system currently has drivers.

cat /proc/devices

To view IP addresses in IPv6 include the -6 argument with ip.

ip -6 address show

View current IP filtering rules.

sudo iptables -L

dmidecode is a tool for dumping a computer's DMI (some say SMBIOS) table contents in a human-readable format. This table contains a description of the system's hardware components, as well as other useful pieces of information such as serial numbers and BIOS revision. Thanks to this table, you can retrieve this information without having to probe for the actual hardware. While this is a good point in terms of report speed and safeness, this also makes the presented information possibly unreliable.

sudo dmidecode --type connector | less

Find motherboard/system model.

sudo dmidecode --string system-product-name

Use cases

Mount a portable USB hard disk plugged into a server.

1. Use sudo lsscsi to find the device and associated device file.

For example, /dev/sdc.

2. Use sudo parted -l to find out the parition table type, partitions, File system and the disk size.

For example, the partition table is gpt, with two partitions, using the ntfs File system.

3. (Optional) Find UUID using sudo blkid and looking for the device file.
4. Mount using mount.

For example:

sudo mkdir -p /mnt/media/my_hd
sudo mount -t ntfs /dev/sdc2 /mnt/media/my_hd

If you get the following error:

mount: unknown filesystem type 'ntfs'

Install ntfs-3g:

# RHEL/CentOS/Fedora
sudo yum install ntfs-3g

# Ubuntu/Debian
sudo apt install ntfs-3g

5. Once you are done unmount using umount and make sure you're not in the mount point directory.

   sudo umount /mnt/media/my_hd