1000 Tips - Thousands of streams merged into the sea

How to implement free HTTPS on your website?

As you know lets-encrypt is free and open Certificate Authority, but how to implement to your website?

Here is a very useful website: Certbot .

For example:

Access the webpage above, following the steps guide, you will implement your website for free HTTPS certificate.

How to update/install glibc-2.14 on centos 6.x

Update reason:

.../node_modules/webp-converter/lib/libwebp_linux/bin/dwebp: /lib64/libc.so.6: version `GLIBC_2.14' not found

1	.../node_modules/webp-converter/lib/libwebp_linux/bin/dwebp: /lib64/libc.so.6: version `GLIBC_2.14' not found

check installed glibc version:

[root@xxxx&nbsp;lib64]# ldd --version
ldd (GNU libc) 2.12

1 2	[[email protected] lib64]# ldd --version ldd (GNU libc) 2.12

I have tried update glibc like below:

yum update glibc

1	yum update glibc

but didn’t work, so tried the solution like below steps:

download glibc-2.14.tar.gz

extract the download files and build, install in /opt/glibc-2.14:

[root@xxx ~]#tar -xzvf glibc-2.14.tar.gz
[root@xxx ~]#cd glibc-2.14
[root@xxx glibc-2.14]# mkdir build
[root@xxx glibc-2.14]# cd build
[root@xxx build]# ../configure --prefix=/opt/glibc-2.14
[root@xxx build]# make -j4
[root@xxx build]# make install

[[email protected] ~]#tar -xzvf glibc-2.14.tar.gz

[[email protected] ~]#cd glibc-2.14

[[email protected] glibc-2.14]# mkdir build

[[email protected] glibc-2.14]# cd build

[[email protected] build]# ../configure --prefix=/opt/glibc-2.14

[[email protected] build]# make -j4

[[email protected] build]# make install

update glibc symbolic links:

[root@xxxx lib64]rm -rf /lib64/libc.so.6
[root@xxxx lib64]LD_PRELOAD=/opt/glibc-2.14/lib/libc-2.14.so  ln -s /opt/glibc-2.14/lib/libc-2.14.so /lib64/libc.so.6

1 2	[[email protected] lib64]rm -rf /lib64/libc.so.6 [[email protected] lib64]LD_PRELOAD=/opt/glibc-2.14/lib/libc-2.14.so ln -s /opt/glibc-2.14/lib/libc-2.14.so /lib64/libc.so.6

If you want restore glibc symbolic links :

[root@xxxx lib64]rm -rf /lib64/libc.so.6
[root@xxxx lib64]$ LD_PRELOAD=/lib64/libc-2.12.so ln -s /lib64/libc-2.12.so /lib64/libc.so.6

1 2	[[email protected] lib64]rm -rf /lib64/libc.so.6 [[email protected] lib64]$ LD_PRELOAD=/lib64/libc-2.12.so ln -s /lib64/libc-2.12.so /lib64/libc.so.6

How to find files created on a specific date?

1.How to find files modified / created / accessed on a specific date

Example 1: find files modified on the 10th of December

$ find . -type f -newermt 2018-12-10 ! -newermt 2018-12-11

1	$ find . -type f -newermt 2018-12-10 ! -newermt 2018-12-11

Example 2: find files created on the 10th of December

$ find . -type f -newerct 2018-12-10 ! -newerct 2018-12-11

1	$ find . -type f -newerct 2018-12-10 ! -newerct 2018-12-11

Example 3: find files accessed on the 10th of December

$ find . -type f -newerat 2018-12-10 ! -newerat 2018-12-11

1	$ find . -type f -newerat 2018-12-10 ! -newerat 2018-12-11

2.Then how to use find to delete the files found above

 find . -type f -newermt 2018-12-10 ! -newermt 2018-12-11 -exec rm -rf {} \;

1	find . -type f -newermt 2018-12-10 ! -newermt 2018-12-11 -exec rm -rf {} \;

How to install Node.js and NPM on Centos?

Before installation, please check your server operation system, this time we will install node.js on centos 6.7:

# cat /etc/centos-release
CentOS release 6.7 (Final)

1 2	# cat /etc/centos-release CentOS release 6.7 (Final)

Then you can check which yum repository you should use, please read Node.js Binary Distributions to find the yum repository

Step 1. Add node.js yum repository

curl -sL https://rpm.nodesource.com/setup_8.x | sudo -E bash -

1	curl -sL https://rpm.nodesource.com/setup_8.x \| sudo -E bash -

In my case, I chosed NodeJS 8.x on CentOS 6

Step 2: Install node.js and NPM

yum install nodejs

1	yum install nodejs

After the command complete, node.js and npm are both installed completely (also include some other dependent packages).

Step 3: Verify versions

Now we can check the node.js and npm version like below:

#node -v
v8.11.3

# npm -v
5.6.0

#node -v

v8.11.3

# npm -v

5.6.0

How to check changes before pulling from remote git repository

Check changes before pulling from remote git repository steps below:

fetch the changes from the remote

Shell

git fetch origin

1

git fetch origin
show commit logs of changes

Shell

git log master..origin/master

1

git log master..origin/master
show diffs of changes

Shell

git diff master..origin/master

1

git diff master..origin/master
apply the changes by merge..

Shell

git merge origin/master

1

git merge origin/master

Difference between Git Pull vs Git Fetch:

Git pull will download and merge latest changes from the remote repository automatically. You don’t have chance to review the changes and conflicts.

Git fetch will only download lastest changes but won’t merge. You can use git diff to review the changes and conflicts, then use git merge to merge the changes.

How to use iptables to defend against reflection DDOS attack on Centos

Usually use iptables to drop the UDP fragmented packets, below is the iptables config example:

vi /etc/sysconfig/iptables

-A INPUT -i eth1 -p udp -m udp -m multiport --dports 19,53,111,123,161,1121,1900 -j DROP
-A INPUT -i eth1 -p udp -m udp -m multiport --sports 19,53,111,123,161,1121,1900 -j DROP
-A OUTPUT -o eth1 -p udp -m udp -m multiport --dports 19,53,111,123,161,1121,1900 -j DROP
-A OUTPUT -o eth1 -p udp -m udp -m multiport --sports 19,53,111,123,161,1121,1900 -j DROP

-A INPUT -i eth1 -p udp -m udp -m multiport --dports 19,53,111,123,161,1121,1900 -j DROP

-A INPUT -i eth1 -p udp -m udp -m multiport --sports 19,53,111,123,161,1121,1900 -j DROP

-A OUTPUT -o eth1 -p udp -m udp -m multiport --dports 19,53,111,123,161,1121,1900 -j DROP

-A OUTPUT -o eth1 -p udp -m udp -m multiport --sports 19,53,111,123,161,1121,1900 -j DROP

Reference:

1 HOW TO DEFEND AGAINST AMPLIFIED REFLECTION DDOS ATTACKS

2 DDoS attacks – an explanation of amplified reflective UDP-based attacks

AWS reinvent 2018 Slides index

Let’s take a look at AWS reinvent 2018 from these slides

You also can check more slide from AWS on slidesshare.net

How to connect Amazon EC2 Linux Instance if you lose Private Key

From AWS EC2 Management Console, click Instances, select the original instance (that you lose the private key)
Memo the detail information of the original instance:
- the instance ID (i-xxxxxxxx), AMI ID (ami-xxxxxxxx), and Availability Zone of the original instance from the details pane.
- volume ID in the EBS ID field (vol-xxxxxxxx) under Block devices the details pane.
- [EC2-Classic] If the original instance has an associated Elastic IP address, write down the Elastic IP address shown under Elastic IP in the details pane.
Select the original instance to click stop.
Launch a new instance with same config as the original instance. You can tag the new instance as Name=Temporary and create a new key pair, download it.
Click Volumes in the navigation pane, select the root device volume for the original instance. Click Detach Volume to detach the volum. Wait for the state of the volume to become available. (You might need to click the Refresh icon.)
Atach the original instance’s root volume to the new instance and specify the device name (for example, /dev/sdf ) .
Use PuTTY to connect the new instance via SSH.

Mount the root device volume for the original instance to the new instance.

Use the lsblk command to determine if the volume is partitioned.

[ec2-user ~]$ lsblk
NAME    MAJ:MIN RM  SIZE RO TYPE MOUNTPOINT
xvda    202:0    0    8G  0 disk
└─xvda1 202:1    0    8G  0 part /
xvdf    202:80   0  101G  0 disk
└─xvdf1 202:81   0  101G  0 part
xvdg    202:96   0   30G  0 disk

[ec2-user ~]$ lsblk

NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT

xvda 202:0 0 8G 0 disk

└─xvda1 202:1 0 8G 0 part /

xvdf 202:80 0 101G 0 disk

└─xvdf1 202:81 0 101G 0 part

xvdg 202:96 0 30G 0 disk

In the above example, /dev/xvda and /dev/xvdf are partitioned volumes, and /dev/xvdg is not. If your volume is partitioned, you mount the partition (/dev/xvdf1) instead of the raw device (/dev/xvdf) in the next steps.

Create a temporary directory to mount the volume.

Shell

[ec2-user ~]$ sudo mkdir /mnt/tempvol

1

[ec2-user ~]$ sudo mkdir /mnt/tempvol
Mount the volume (or partition) at the temporary mount point, using the volume name or device name you identified earlier.

Shell

[ec2-user ~]$ sudo mount /dev/xvdf1 /mnt/tempvol

1

[ec2-user ~]$ sudo mount /dev/xvdf1 /mnt/tempvol

Use the new instance’s authorized_keys to update the original instance‘s authorized_keys

Shell

[ec2-user ~]$ cp .ssh/authorized_keys /mnt/tempvol/home/ec2-user/.ssh/authorized_keys

1

[ec2-user ~]$ cp .ssh/authorized_keys /mnt/tempvol/home/ec2-user/.ssh/authorized_keys

If copy failed, please modify the file permission.
Unmount the /mnt/tempvol

Shell

[ec2-user ~]$ sudo umount /mnt/tempvol

1

[ec2-user ~]$ sudo umount /mnt/tempvol

So you can reattach it to the original instance again
From the Amazon EC2 Management Console, select the original instance’s volume, click Actions, and then click Detach Volume. Wait for the state of the volume to become available. (You might need to click the Refresh icon.)
Then select original instance’s volume, click Actions and click Attach Volume. Select the original instance ID, specify the device name that you memoed (for example, /dev/xvda), and then click Yes, Attach.
Select the original instance to start. After the instance’s state becomes running , you can connect to it using the private key file for your new key pair.

How to fix: Mysql ERROR 1820 (HY000): You must SET PASSWORD before executing this statement

The error means the logined user’s password was expired, you excute the sql to confirm:

mysql>SELECT user,host,password,password_expired FROM mysql.user;

1	mysql>SELECT user,host,password,password_expired FROM mysql.user;

To resolve the error , you can reset the password:

mysql>SET PASSWORD=PASSWORD('your password');

1	mysql>SET PASSWORD=PASSWORD('your password');

If you got error, you also can drop the user and create it again.

Tutorial: How to install wordpress on AWS EC2 t2.micro instance ? Charpter-1

Charpter-1: How to install AWS EC2 t2.micro instance

Before installing wordpress on AWS EC2 t2.micro instance (server), we have to prepair an AWS EC2 instance.

In this article I will introduce how to install a free tier AWS EC2 t2.micro instance.

1. Choose an Amazon Machine Image (AMI)

We selected “Amazon Linux AMI 2014.09.2 (HVM) – ami” to install.

PS: There is another AIM “Amazon Linux AMI 2014.09.2 (PV) – ami“. PV type AMI has smaller memory and lower network performance than HVM type in free tier.