compiling on macbook - xcrun error

error:

xcrun: error: invalid active developer path

solution:

1. install xcode

2. xcode-select --install

* The long retry limit - default 4: applies to frames longer than the RTS threshold.

        A frame requiring RTS/CTS clearing is retransmitted four times before it is discarded and reported to higher-level protocols.

* The short retry limit - default 7: applies to frames shorter than the RTS threshold.

Adding a dummy monitor

 

sudo apt-get install xserver-xorg-video-dummy

sudo vi /etc/X11/xorg.conf

Section "Device"

    Identifier  "Configured Video Device"

    Driver      "dummy"

EndSection

Section "Monitor"

    Identifier  "Configured Monitor"

    HorizSync 31.5-48.5

    VertRefresh 50-70

EndSection

Section "Screen"

    Identifier  "Default Screen"

    Monitor     "Configured Monitor"

    Device      "Configured Video Device"

    DefaultDepth 24

    SubSection "Display"

    Depth 24

    Modes "1024x800"

    EndSubSection

EndSection

Disabling DHCP and DNS role - OpenWrt

uci set dhcp.lan.ignore="1"

uci set dhcp.@dnsmasq[0].port="0"

uci commit dhcp

/etc/init.d/dnsmasq restart

/etc/init.d/odhcpd restart

kernel config config.gz

zcat /proc/config.gz

zcat /proc/config.gz | grep SKB

ifdef if defined if !defined

#if defined(LINUX) || defined(ANDROID)

#if !defined(MANUF) || !defined(SERIAL) || !defined(MODEL)

#if defined(LINUX) && !defined(MODEL)

#endif

shell if statement

reference: https://ryanstutorials.net/bash-scripting-tutorial/bash-if-statements.php

if [ <some test> ]
then
<commands>
fi

================== compare number ================
#!/bin/bash
# Basic if statement
if [ $1 -gt 100 ]
then
    echo Hey that\'s a large number.
    pwd
fi
================== compare string ================
#!/bin/sh
if [ -z $1 ]
then
   echo "no input string given"
   return
fi
==============================================

Operator	Description
! EXPRESSION	The EXPRESSION is false.
-n STRING	The length of STRING is greater than zero.
-z STRING	The lengh of STRING is zero (ie it is empty).
STRING1 = STRING2	STRING1 is equal to STRING2
STRING1 != STRING2	STRING1 is not equal to STRING2
INTEGER1 -eq INTEGER2	INTEGER1 is numerically equal to INTEGER2
INTEGER1 -gt INTEGER2	INTEGER1 is numerically greater than INTEGER2
INTEGER1 -lt INTEGER2	INTEGER1 is numerically less than INTEGER2
-d FILE	FILE exists and is a directory.
-e FILE	FILE exists.
-r FILE	FILE exists and the read permission is granted.
-s FILE	FILE exists and it's size is greater than zero (ie. it is not empty).
-w FILE	FILE exists and the write permission is granted.
-x FILE	FILE exists and the execute permission is granted.

= is slightly different to -eq. [ 001 = 1 ] will return false as = does a string comparison (ie. character for character the same) whereas -eq does a numerical comparison meaning [ 001 -eq 1 ] will return true.

When we refer to FILE above we are actually meaning a path. Remember that a path may be absolute or relative and may refer to a file or a directory.

bash> test 001 = 1

bash> echo $?

bash> 1

bash> test 001 -eq 1

bash> echo $?

bash> 0

bash> touch myfile

bash> test -s myfile

bash> echo $?

bash> 1

bash> ls /etc > myfile

bash> test -s myfile

bash> echo $?

bash> 0

How to configure routing between LAN and WAN

https://monoinfinito.wordpress.com/series/setting-up-a-linux-gatewayrouter-a-guide-for-non-network-admins/

dhcp perf tools

1. How to install
    kea-admin contains perfdhcp binary

$ sudo apt install kea-admin

$ sudo perfdhcp -p 60 -r 100 -d 5 -R 50 192.168.1.1

2. User manual
https://users.isc.org/~tomasz/perfdhcp/dhcp-perf-guide.html#perfdhcp-commandline-examples
- adding delayed-ack 32 that allows packets to queue before send
- max-ack-delay that increase time to fsync
- ping-check false
- dont-use-fsync to true

3. Build your own
    build/install from source

$ sudo apt -y install automake libtool pkg-config build-essential ccache

$ sudo apt -y install libboost-dev libboost-system-dev liblog4cplus-dev libssl-dev

$ git clone https://gitlab.isc.org/isc-projects/kea.git

$ cd kea

$ autoreconf --install

$ ./configure [your additional options here]

$ make -j4

$ sudo make install

$ echo "/usr/local/lib/hooks" > /etc/ld.so.conf.d/kea.conf

$ ldconfig

git submodule

*** sync submodule

$ git checkout master

M meta-openembedded

M poky

$ git submodule update

git submodule add https://git.kernel.org/pub/scm/linux/kernel src/linux

git config examples)
.git/config
[submodule "linux"]
url = https://git.kernel.org/pub/scm/linux/kernel

.gitmodules
[submodule "linux-msm"]
path = src/linux
url = https://git.kernel.org/pub/scm/linux/kernel
rev = b27efee486f8a24682f36908fb2693a7b310303b

git clone --recurse-submodules --branch <branch name> <git url>

git clone --single-branch --recurse-submodules --branch <branch name> <git url>

git submodule sync
    Synchronizing submodule url for 'xxx'
    fatal: no submodule mapping found in .gitmodules for path 'yyy'
git rm -r yyy --cached

trouble shootings)
git rm --cached src/linux
rm -rf src/linux
rm -rf .git/modules/src/linux

git submodule [--quiet] add [-b branch] [-f|--force]
      [--reference <repository>] [--] <repository> [<path>]
git submodule [--quiet] status [--cached] [--recursive] [--] [<path>…​]
git submodule [--quiet] init [--] [<path>…​]
git submodule [--quiet] update [--init] [-N|--no-fetch] [--rebase]
      [--reference <repository>] [--merge] [--recursive] [--] [<path>…​]
git submodule [--quiet] summary [--cached|--files] [--summary-limit <n>] [commit] [--] [<path>…​]
git submodule [--quiet] foreach [--recursive] <command>
git submodule [--quiet] sync [--] [<path>…​]


*** Update git submodule to their remote origin

# Get the submodule initially
git submodule add ssh://bla submodule_dir
git submodule init

# Time passes, submodule upstream is updated
# and you now want to update

# Change to the submodule directory
cd submodule_dir

# Checkout desired branch
git checkout master

# Update
git pull

# Get back to your project root
cd ..

# Now the submodules are in the state you want, so
git commit -am "Pulled down update to submodule_dir"


git submodule foreach git pull origin master

mount squashfs image on ubuntu

sudo mount -o loop -t squashfs ./root.squashfs ./mnt

apt clean

sudo rm /var/lib/apt/lists/*
sudo rm /var/cache/apt/*.bin

sudo apt update

VirtualBox clone / resize

/Users/peteroh/VirtualBox VMs/Ubuntu-16.04/Ubuntu-16.04.vdi

VBoxManage clonehd Ubuntu-16.04.vdi Ubuntu-16.04-2.vdi --format VDI --variant Standard

VBoxManage modifyhd Ubuntu-16.04.vdi --resize 50000