Linux - Internal hardware

Hardware detection utilities :

• lspci (from pciutils)
• lsusb (from usbutils)
• lshw (from lshw)
• discover
• lshal : show vendor, product name, S/N, /sys/device path, ... (details)

One-liner to get CPU and RAM from a list of servers via SSH :

Motherboard

• Model reference : dmidecode -t baseboard | grep "Base Board Information" -A13
• SATA capabilities (bandwidth of SATA versions, I:1.5Gb/s, II:3Gb/s, III:6Gb/s) : dmesg | grep -i sata

CPU

• lscpu
• less /proc/cpuinfo (Differentiate multi-core / multi-socket / hyperthreading CPUs)
• dmidecode -t processor (requires root privileges)
• Number of physical processors : grep 'physical id' /proc/cpuinfo | sort -u | wc -l
• Number of cores :
  • grep -Ec '^processor' /proc/cpuinfo
  • top + 1
  • nproc
• Whether the processor is a 32/64 bits :
  • method 1 : arch
  • method 2 : This command checks whether the kernel is 32 or 64 bit (source) : getconf LONG_BIT
    • 64 / ia64 / x86_64 : 64-bit mode
    • 32 / i386 : 32-bit mode
  • method 3 : perl -e 'print ~123;'; echo
    • 4294967172 : 32 bits
    • 18446744073709551492 : 64 bits

RAM

• less /proc/meminfo
• Total installed RAM :
  • raw : grep "MemTotal:" /proc/meminfo
  • in GiB : awk '/MemTotal:/ {printf "%.0fGiB\n", $2/1024/1024}' /proc/meminfo
• the shell command free
• dmidecode -t memory (requires root privileges)

video card / GPU (source) :

• with lspci :
  1. lspci | grep VGA

     00:02.0 VGA compatible controller: Intel Corporation CometLake-U GT2 [UHD Graphics] (rev 02)

  2. lspci -v -s 00:02.0

     00:02.0 VGA compatible controller: Intel Corporation CometLake-U GT2 [UHD Graphics] (rev 02) (prog-if 00 [VGA controller])
     	DeviceName: Onboard - Video
     	Subsystem: Dell CometLake-U GT2 [UHD Graphics]
     	Flags: bus master, fast devsel, latency 0, IRQ 158
     	Memory at cb000000 (64-bit, non-prefetchable) [size=16M]
     	Memory at 80000000 (64-bit, prefetchable) [size=256M]
     	I/O ports at 3000 [size=64]
     	Expansion ROM at 000c0000 [virtual] [disabled] [size=128K]
     	Capabilities: <access denied>					run command as root for full details
     	Kernel driver in use: i915
     	Kernel modules: i915

• glxinfo

HDD and storage devices

• List storage (aka block) devices : lsblk
• Manufacturer, model number, S/N, firmware and A LOT more :
  • hdparm -I /dev/sdb
    For details on all installed drives : for letter in {a..z}; do device="/dev/sd$letter"; [ -b "$device" ] && hdparm -I "$device" | head -8; done
  • smartctl -a /dev/sdb (this comes with smartmontools, more from Wikipedia, more from Ubuntu documentation)
• List available partitions :
  • fdisk -l
  • or less /proc/partitions
  • or mount | grep sd
  • or grep sd /etc/mtab
• Get device / filesystem metadata (type, last mount point, status, FS creation/last mount/last write/last check/next check, mount count, ...)
• Get partitions size, usage, available space : df -h
• Get device / partition size :
  • fdisk -l | grep -E '^Disk /'
  • Using the /sys pseudo filesystem :

    in sectors	in GiB (1 sector = 512 B)
    cat /sys/block/sda/size cat /sys/block/sda/sda1/size	echo "$(cat /sys/block/sda/size)*512/1024/1024/1024" | bc echo "$(cat /sys/block/sda/sda1/size)*512/1024/1024/1024" | bc

• Total storage :
  • df -m | awk '/^\/dev/ { sum += $2 } END { print sum/1024 }'
  • awk '{ sum += $1 } END { print sum*512/1024/1024/1024 }' /sys/class/scsi_disk/*/device/block/*/size

  Both methods give slightly different numbers. I guess this is because the df method sums formatted sizes whereas the /sys method gets device size.

• Sector size :
  • fdisk -l device
  • parted device print

SATA drives speed (source) :

SWAP usage in MB

LAN

PCI devices

• less /proc/pci (when available)
• lspci lists all detected PCI devices (in a tree-like diagram with -tv : tree + verbose) :

  ...
  00:18.4 Host bridge: Advanced Micro Devices [AMD] Family 10h Processor Link Control
  01:00.0 VGA compatible controller: ATI Technologies Inc Juniper [Radeon HD 5700 Series]
  01:00.1 Audio device: ATI Technologies Inc Juniper HDMI Audio [Radeon HD 5700 Series]
  ...

  For more details on device (source) : lspci -v -s 01:00.0

  01:00.0 VGA compatible controller: ATI Technologies Inc Juniper [Radeon HD 5700 Series] (prog-if 00 [VGA controller])
  Subsystem: PC Partner Limited Device 1482
  Flags: bus master, fast devsel, latency 0, IRQ 27
  Memory at d0000000 (64-bit, prefetchable) [size=256M]

• scanpci -vO (-v : verbose, -O : use the OS's specific mechanism to get information. details). The PCI bus 0x1 is the AGP port.

USB devices

Monitor (inspired by)

	RADEON(0): Monitor name: PL1980
	RADEON(0): EDID vendor "IVM", prod id 18500

Kernel

Operating system

Operating system installation date (source)

List daemons / services

• managed by SysVinit : service --status-all
• managed by Upstart : initctl list
• managed by systemd : systemctl list-units

Current shell

• ps $$
• echo $0

Environment variables

• env
• More about environment variables

Files

• get the file type : file myFile
• information on file times : stat myFile
• information (type, dimension, colors) of image files : identify myFile

• Investigate (cat / more / less) the /proc/ directory
• dmesg | less displays the kernel messages.
• Read logs :
  • /var/log/messages
  • /var/log/boot.log
  To read logs in real time : tail -f /var/log/messages
• List the loaded kernel modules (details) : lsmod

1. By typing dmesg, you may notice a message such as b43-phy0 ERROR : Firmware file "B43/ucode5.fw" not found or load failed. This means the WiFi controller firmware is missing.
2. So let's install it : apt install b43-fwcutter. The installer will ask whether to unpack it all : accept.
3. unload and reload the kernel module : rmmod b43 && modprobe b43
   if using a PCMCIA WiFi controller, its LEDs should light up once the module is loaded

1. The 1^st thing you'll need is the Intel firmware ipw2200-bss.fw (alternate source). This firmware is required during the system setup.
2. Some packages to install :
   • wireless-tools
   • wpasupplicant
3. Let's encrypt our WPA passphrase : wpa_passphrase mySsid myUnencryptedPassphrase, which outputs :

   network={
   ssid="mySsid"
   #psk="myUnencryptedPassphrase"
   psk=600792632e29fc6c69f04e82d1290a28bf1bffff58294ca6ddaf48062c36f311
   }

4. Then, let's save this into /etc/network/interfaces
   • static version :

     # Static configuration
     auto wlan0
     iface wlan0 inet static
     address 192.168.0.2
     netmask 255.255.255.0
     network 192.168.1.0
     broadcast 192.168.1.255
     gateway 192.168.0.1
     wpa-conf managed
     wpa-ap-scan 1
     wpa-scan-ssid 1
     wpa-ssid mySsid
     wpa-key-mgmt WPA-PSK
     wpa-psk 600792632e29fc6c69f04e82d1290a28bf1bffff58294ca6ddaf48062c36f311

   • DHCP version :

     # DHCP configuration
     auto wlan0
     iface wlan0 inet dhcp
     wpa-conf managed
     wpa-ap-scan 1
     wpa-scan-ssid 1
     wpa-ssid mySsid
     wpa-key-mgmt WPA-PSK
     wpa-psk 600792632e29fc6c69f04e82d1290a28bf1bffff58294ca6ddaf48062c36f311

5. Then, restart the network to load changes : /etc/init.d/networking restart

   In some circumstances, it may be required to allow broadcasting the SSID so that the wireless host can discover it. Once the wireless host has been registered to the access point, SSID broadcasting can be turned off.

   This may also be related to MAC addresses filtering : while SSID broadcasting was off, my own wireless network was invisible to scanning.

1. To "see" the system complain, run /etc/init.d/network-manager restart && dmesg. You may notice an output like :

   [109694.622325] firmware: requesting iwlwifi-3945-1.ucode
   [109694.631281] iwl3945: iwlwifi-3945-1.ucode firmware file req failed: Reason -2
   [109694.631281] iwl3945: Could not read microcode: -2

   We need the firmware file iwlwifi-3945-1.ucode.
2. Let's get it from intellinuxwireless.org (alternate source)
3. copy it into /lib/firmware/
4. edit /etc/network/interfaces :

   auto wlan0
   iface wlan0 inet dhcp
   	wireless-essid myEssid
   	wireless-key myWepKey

5. enable the interface with ifup wlan0

1. normal setup is done with : iwconfig wlan0 essid mySsid freq 2447000000 ap accessPointMacAddress rate 54M
2. then, as root : iwconfig wlan0 rate 54M
3. ... and it should work ! (source)

There's a popular belief saying that the swappiness is the RAM usage threshold beyond which some of the contents of the RAM is moved to the SWAP partition. Based on the 60 default value, it's said that, if the free RAM goes below 60%, the SWAP will be used.

Myths about Swap (source) :

For more details and definitions :

echo 10 > /proc/sys/vm/swappiness

This command will work fine (it will cause no error, no silenced warning will be generated) but it's mostly pointless unless PERFECTLY understanding how the swap works. Again, changing the swappiness value has NOTHING to do with any amount of used RAM after which swapping starts. Read links above.

vm.swappiness=10

• Superb : no swap space even has been allocated (free shows 0 swap in use), and RAM usage is low. Unless you benefit from a huge filesystem cache, you may have spent too much on RAM. Run more stuff.
• Great : swap space is allocated, but there is almost no I/O on the swap partition.
• OK : swap space is allocated, and there is some I/O on the swap partition. System throughput is still OK. For example, the CPUs are busy, and most of that is in the User or Nice categories. If you see CPU Wait, it indicates a disk bottleneck (possibly on swapping), and system time could mean the OS is frantically looking for memory to reuse (page scanning).
• Not OK :
  • too much swapping : lots of I/O on the swap partition. CPU is spending a lot of time in Sys or Wait, and swap disk service times exceed the average disk access times
  • too little swap space : system is running very well, but new programs refuse to start due to lack of virtual memory

• separator=','; for file in /proc/*/status; do grep -q 'VmSwap' $file && awk -v separator="$separator" '/Name/ {printf $2""separator} /VmSwap/ {print $2""separator""$3}' $file; done | sort -t "$separator" -k 2 -nr | head -20 | column -s "$separator" -t
• for file in /proc/*/status; do awk '/VmSwap|Name/ { printf $2 " " $3 } END { print "" }' $file; done | sort -k 2 -nr | head -20

TARGET	SOURCE	FSTYPE	OPTIONS
/tmp	tmpfs	tmpfs	rw,nosuid,nodev,relatime,size=307200k

• tmpfs volumes can be read/written like any other filesystem type, but they are on volatile memory instead of a persistent storage device : their contents is not reboot-proof.
• The memory used by tmpfs grows and shrinks to accommodate the files it contains and can be swapped out to swap space. By default, swapping is triggered by data on the tmpfs volume using more than half of the physical RAM.
• Depending on distributions, /tmp itself can be a tmpfs volume

/dev/shm vs /run/shm vs /tmp :

Create a custom ramdisk (source) :

Create a custom ramdisk at boot time :

none	/mount/point	tmpfs	defaults,size=512M	0	0

Change ramdisk size :

1. echo blacklist pcspkr > /etc/modprobe.d/pcspkr.conf
2. depmod -a
3. update-initramfs -u
4. reboot

• First 446 bytes contain bootable code.
• Next 64 bytes contain partition information for 4 partitions (16×4). That is why the hard disks can have only 4 primary partitions, as the MBR can store information for 4 partitions only. So if you need more than 4 partitions on the hard disk, one of the primary partition has to be made extended, and out of this extended partition, logical partitions are created.
• Last 2 bytes are for MBR signature, also called magic number.

|=================|======|======|======|======|===|
| 446             | 16   | 16   | 16   | 16   | 2 |
|=================|======|======|======|======|===|

Save the MBR :

dd if=/dev/sda of=/path/to/file bs=446 count=1

Save the MBR + partition table :

dd if=/dev/sda of=/path/to/file bs=512 count=1

Restore one of those :

dd if=/path/to/file of=/dev/sda bs=446|512 count=1