MyNotes

Remove comments from Bash file

grep -o '^[^#]*' file

-o: prints only matched part of the line
first ^: beginning of the line
[^#]*: any character except # repeated zero or more times

Find string from files

grep -nwr /path/to/search -e "word"

Change vm root password

First mount the disk somewhere on the host. I created a directory called a, and mounted it there.

qemu-nbd -c /dev/nbd0 *.qcow2 
mount /dev/nbd0p1 a

Change directory to a, and change the root password by modifying /etc/shadow:

perl -pe 's|(?<=root:)[^:]*|crypt("my_new_password","\$6\$some_salt\$")|e' etc/shadow > root/shadow
cp root/shadow etc/
rm root/shadow

Then unmount it:

umount /dev/nbd0p1
qemu-nbd -d /dev/nbd0

Start subl from terminal

ln -s /Applications/Sublime\ Text.app/Contents/SharedSupport/bin/subl /usr/local/bin/subl

Remove dependencies for homebrew formula

brew rm FORMULA
brew rm $(join <(brew leaves) <(brew deps FORMULA))

Run brew rm $(join <(brew leaves) <(brew deps FORMULA)) multiple times until it says This command requires a keg argument. Then run brew doctor to check dependencies missing. Finally run brew cleanup.

Install go from homebrew

brew install go --cross-compile-all

Build go project for many platforms

GOOS=windows GOARCH=386 go install
GOOS=windows GOARCH=amd64 go install

GOOS=linux GOARCH=386 go install
GOOS=linux GOARCH=amd64 go install
GOOS=linux GOARCH=arm go install

GOOS=darwin GOARCH=386 go install
GOOS=darwin GOARCH=amd64 go install

GOOS=freebsd GOARCH=386 go install
GOOS=freebsd GOARCH=amd64 go install

GOOS=netbsd GOARCH=386 go install
GOOS=netbsd GOARCH=amd64 go install

GOOS=openbsd GOARCH=386 go install
GOOS=openbsd GOARCH=amd64 go install

Disconnect from svn

find . -name .svn | xargs rm -Rf

Show all files

defaults write com.apple.finder AppleShowAllFiles TRUE
killall Finder

Disable dashboard

defaults write com.apple.dashboard mcx-disabled -boolean YES
killall Dock

Iframe to talk to parent

child -> parent: 
window.parent.document.getDocumentById('dom_id');  

parent -> child: 
var ifrm = document.getElementById('my_iframe');  
ifrm = (ifrm.contentWindow) ? ifrm.contentWindow : (ifrm.contentDocument.document) ? ifrm.contentDocument.document : ifrm.contentDocument;  
var my_dom = ifrm.document.getDocumentById('dom_id');

Generate RSA key pair

ssh-keygen -t rsa

Login ssh without password

target_host="root@192.168.0.1"
ssh ${target_host} mkdir -p .ssh
cat ~/.ssh/id_rsa.pub | ssh ${target_host} "cat >> .ssh/authorized_keys"
ssh ${target_host} chmod 700 .ssh
ssh ${target_host} chmod 640 .ssh/authorized_keys

Sync Postfix user mapping table (Ubuntu)

cp -p /etc/passwd /var/spool/postfix/etc/passwd

Enable Roundcube password plugin to use chpasswd driver

Edit the file /etc/sudoers, then add this line: www-data ALL=NOPASSWD: /usr/sbin/chpasswd under: root ALL=(ALL:ALL) ALL

Persist iptable configurations on Ubuntu

apt-get install iptables-persistent

Adding and deleting zone using rndc

to enable rndc to add new zones, add the following code to /etc/bind/named.conf.options:

allow-new-zones yes;

to add a new zone

rndc addzone mydomain.com  '{type master; file "/etc/bind/db/mydomain.com";};'
rndc addzone mydomain.com '{ type slave; masters { master_ip; }; };'

to add the reserve zone

rndc addzone 0.168.192.in-addr.arpa  '{type master; file "/etc/bind/db/db.192.168.0";};'
rndc addzone 0.168.192.in-addr.arpa '{ type slave; masters { master_ip; }; };'

to reload modified zone

rndc reload mydomain.com
rndc reload 0.168.192.in-addr.arpa

to remove a zone

rndc delzone mydomain.com

Ultimate way to install node/npm with homebrew

$ brew install node --without-npm
$ curl -L https://npmjs.org/install.sh | sh

Please note sudo is NOT used anywhere in the above commands. The reason why I want to install node and npm separately is that homebrew does not like npm to update npm iteslf. homebrew has a philosophy that everything is inside it's Cellar. I personally appreeciate homebrew's clean way of doing things. However npm is just yet another package manager, which is not aware of homebrew's cellars philosophy. Therefore, I prefer to get homebrew to manager node, and let npm manage itself.

Extend logic volume

# lvextend -l +100%FREE /dev/ubuntu0-vg/root
# resize2fs /dev/ubuntu0-vg/root

Detect java executable

#!/bin/bash

if [[ $(which ${JAVA_HOME}/bin/java) ]]; then
	exe="${JAVA_HOME}/bin/java"
elif [[ $(which java) ]]; then
	exe="java"
else 
	echo "Java environment is not detected."
	exit 1
fi

${exe} -version

$ in shell

#$(xxx) execute the output of xxx
$(which "$JAVA_HOME/bin/java") -version

#${xxx} evaluate xxx
${JAVA_HOME}/bin/java -version

iptables for port forwarding

Edit this file /etc/sysctl.conf，and change the value from 0 to 1:

net.ipv4.ip_forward = 1

Run sysctl -p to make the change effective

iptables -t nat -A PREROUTING -p tcp -i eth0 --dport <localPort> -j DNAT --to <remoteIp>:<remotePort>
iptables -t nat -A PREROUTING -p tcp -i eth0 --dport <localPort> -j DNAT --to <remoteIp>:<remotePort>
iptables -t nat -A PREROUTING -p tcp -i eth0 --dport <localPort> -j DNAT --to <remoteIp>:<remotePort>
iptables -t nat -A PREROUTING -p tcp -i eth0 --dport <localPort> -j DNAT --to <remoteIp>:<remotePort>
iptables -t nat -A POSTROUTING -j MASQUERADE

elgs/MyNotes