Disable IPv6 on Raspberry Pi3+

To disable IPv6 and avoid the module loaded in memory just edit /etc/modprobe.d/ipv6.conf:

alias net-pf-10 off
alias ipv6 off
options ipv6 disable_ipv6=1
blacklist ipv6

ChibiOS “undefined reference to `_sbrk'” linker error

If we get this linker error with ChibiOS:

/usr/bin/../lib/gcc/arm-none-eabi/7.3.1/../../../../arm-none-eabi/lib/thumb/v6-m/libg.a(lib_a-sbrkr.o): In function `_sbrk_r':
sbrkr.c:(.text._sbrk_r+0xc): undefined reference to `_sbrk'
collect2: error: ld returned 1 exit status

we simply need to add syscalls.c to be compiled, add the following to CSRC in the Makefile:

$(CHIBIOS)/os/various/syscalls.c

We should underline that _sbrk will work correctly if and only if CH_CFG_USE_MEMCORE == TRUE (editable in chconf.h). Else, malloc() will always return 0 and result in an errno of ENOMEM.

Find machine/host names on the network

Firstly we try to resolve the PTR records in DNS for the specified IP addresses.
It sends nothing to the hosts so there is no guarantee if it is really connected or turned on but we can get the actual DNS map including those devices which are within their DHCP lease timeout.

nmap -sn -sL 192.168.0.0/24

Then we scan for hosts really connected sending ARP requests. The disadvantage is that it only works on your subnet.

nmap -sP 192.168.0.0/24

or if we want to remove useless lines:

nmap -sP 192.168.0.0/24 | grep -E "([0-9]{1,3}[\.]){3}[0-9]{1,3}"

output example:

cesare@cesare-desktop:~$ nmap -sP 192.168.0.0/24 | grep -E "([0-9]{1,3}[\.]){3}[0-9]{1,3}"
 Nmap scan report for router (192.168.0.10)
 Nmap scan report for vpnudp (192.168.0.90)
 Nmap scan report for vpntcp (192.168.0.91)
 Nmap scan report for desktop (192.168.0.100)
 Nmap scan report for unas (192.168.0.110)
 Nmap scan report for pi2 (192.168.0.140)
 Nmap scan report for cloud (192.168.0.200)

or for a better output:

nmap -sP 192.168.0.0/24 | grep -E "([0-9]{1,3}[\.]){3}[0-9]{1,3}" | cut -d ' ' -f5-
router (192.168.0.10)
vpnudp (192.168.0.90)
vpntcp (192.168.0.91)
desktop (192.168.0.100)
unas (192.168.0.110)
cloud (192.168.0.200)

How to install the Virtualbox SDK

Download and extract the SDK package. The target directory will be sdk.

If we try to execute directly the installer we will get:

python sdk/installer/vboxapisetup.py install

Traceback (most recent call last):
  File "sdk/installer/vboxapisetup.py", line 88, in <module>
    main(sys.argv)
  File "sdk/installer/vboxapisetup.py", line 61, in main
    raise Exception("No VBOX_INSTALL_PATH defined, exiting")
Exception: No VBOX_INSTALL_PATH defined, exiting

To install correctly we have to launch locally the install script.

cd sdk/installer

export VBOX_INSTALL_PATH=$(which virtualbox)

sudo -E python vboxapisetup.py install