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Check if a Certain Port is Occupied on Mac

How to check if a certain port is occupied on Mac?

CLI:

Open a Terminal window, and use the command below to check if 80 port is occupied.

Built-in Network Utility Tool

You can also use the Network Utility tool that every Mac comes with.

Just press Command+Spacebar to open the Spotlight Search. Then type the Network Utility to locate the tool. Click the keyboard return/enter key to launch the Network Utility app.

You will find there is a Port Scan tab at the top.mFor example, below I am using the tool to scan all the ports from 0 to 1023, which are also known as “Well-Known Ports”

Mac find port is occupied

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How to Compress Images with Jpegoptim

Jpegoptim is a utility to optimize/compress JPEG files. You can compress JPG format image losslessly with it, or you can set a maximum quality factor to compress the images into even smaller files.

Install Jpegoptim in Ubuntu or CentOS

Ubuntu

Run the commands below to update the package list and install jpegoptim on Ubuntu.

You can check if the installation is successful by running command below to check the version.

Centos

Run the command below to update the package list and install jpegoptim on Centos.

If you are running into an error saying “no package available”, make sure you have repo epel installed and enabled because jpegoptim is a part of epel on Centos.
You can use the command below to list all the enabled repos:

If you don’t see the epel repo in the list, try the command below to enable it.

or install it

Now let’s see some common use cases below:

Losslessly Compress a Single Image

Compress Quality to 80% for all Images in a Folder

Compress Quality to 60% for all Images in a Folder That are larger than 500kb

If you will need a detailed user manual, here is a link https://www.systutorials.com/docs/linux/man/1-jpegoptim/

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How To Install Redis and Configure Multiple Redis Server on Centos 7

What is Redis

You are reading this post, I assume you already have a bit idea what is Redis. But just a short introduction: Redis is an open source in-memory database. It supports basic data type like strings as well as advanced data structures like lists and hashes.Redis is very simple to setup and use. Below is simple instruction on how to install and configure Redis on CentOS 7.

Redis official documentation here

Installation

Run the command below to stall Redis server on Centos.

If you are running into an error saying “no package available”, make sure you have repo epel installed and enabled because redis is a part of epel on Centos.
You can use the command below to list all the enabled repos:

If you don’t see the epel repo in the list, try the command below to enable it.

or install it

Start the Redis Server

Now you can start Redis server and enable to auto-start on system reboot by using the commands below.

By default, Redis server listens on 6379 port, and you can run commands below to check if it is alive.

Install and Run Multiple Instance of Redis on Centos

Sometimes you will need multiple Redis instances, for example I was configuring a server for Magento 2 hosting, and I need 1 server for page cache, 1 for config cache, 1 for session storage.

You can run multiple Redis instances on different ports. By default Redis is installed under /var/lib/redis. This is considered as the work space for the default Redis insane. Memory dump is stored here. You will see a file named dump.rdb if there is any data dumped from memory.

First, to setup another Redis instance, we will need to duplicate the directory for a new instance. You can do so by running the commands below:

Second, we will need to create a separate configuration file. The default config file is /etc/redis.conf

And update configuration in the file to let the new instance run on different ports.

Lines need to be updated:

As you can see above, this time we are using port 6380 to host the new instance.
Then create separate service file for Centos.

Lines need to be updated in the new service file

Now it is time to start the new instance and enable to auto-start on system reboot just like what we did when we install the first instance.

Check the status or our second instance:

Now we have 2 Redis servers running separately on porst 6379 and 6380.

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Linux How to Use du Command to List Files, Directories, and their total sizes

We know we can use ls command to list out all the files and directories under a given directory.

But it doesn’t give us size information. Sometimes, size information is important, for example we are examining a code repository, and need to find out and clean up large files and directories.

Linux List Files, Directories, and Their Total Sizes

du command, short for disk usage, can be useful in case like this. It is used to estimate file space usage.
To list all files, directories, and their total sizes, first cd to the directory, and run the command below.

It will give us an output like below:

List Files, Directories, and their total sizes

Linux List Total Size of Current Directory

To simply list the size of current directory, first cd to the directory, and run the command below.

It will calculate the current directory size:

Linux List Total Size of Current Directory

Linux List Files, Directories, and Their Total Sizes in Descending Order

We’ve already known how to list the size for all files and directories in a certain directory, but can we take one more step further to sort the results.

Then answer is YES! See the command below:

We will need to drop the -h argument, since it will give you human readable output, e.g. 10K, 2.5MB, and they cannot be sorted when we pipe the output to sort command.

Linux List Files, Directories, and Their Total Sizes in Descending Order

Linux Find the Top 10 Largest Files or Directories in Current Directory

We can pass the output from previous command to a head command to accomplish this.

Linux List the Top 10 Largest Files or Directories

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How to Find and Remove Hanging Cron Jobs in Magento

Recently, one of our Magento client reported that their website stopped sending out order confirmation. However, invoice and shipment emails seemed to work with no issue. After an investigation, we discovered their site has caused a hanging Cron Jobs.

How to Find and Remove Hanging Cron Jobs in Magento

Starting from version 1.9.1, order confirmation emails are not sent directly during checkout, instead, they are queued in Magento, and then send out later by execution of Cron Jobs. A hanging Cron Job will cause email send stopped.

Check if Magento Cron Jobs is Hanging

Log into the server and run the following command:

As the screenshot below, you can see a couple lines of outputs

Magento Hanging Cron Jobs

The first line is the Cron daemon process running on this server.

The second line shows the command we just ran.

The third and fourth lines are Magento Cron Jobs that are currently being executed.

Furthermore, take a look at the second column from the right, that is the execution time of the process. Magento Cron Jobs usually runs real quick. So if it is caught by our ps command, and showing a long execution time, I would say if it is longer than 30 mins,  then it is possibly hanging.

Kill Hanging Cron Job

Now find the pid(second column) of the hanging process ending with ‘-mdefault’, in our case above, which is 10231, kill the process with the command below.

Make sure replace  10231 with the pid showing on your console, and you may run the ps aufx | grep cron command again to confirm the hanging Cron Job is killed.  Your Magento Cron Job should resume momentarily.

Usually, following the procedure above will resolve the hanging Cron Job for Magent, but if the Cron Job is still not working normally, or becomes hanging again. I suggest:, First check if you have your Magento Cron Job setup correctly. Check this post if you are not sure how to configure Magento Cron Job.

You can also try doing a truncate (delete all records) for table cron_schedule, and then run the commands again, see if new Cron Job tasks are populated in the cron_schedule table. Additionally, identifying the Cron Job task that is hanging with RUNNING status in the cron_schedule table may help you locate the module which is causing the hanging Cron Job.

 

 

 

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List All Failed SSH Login and Group by IP Address on Centos

Surprised by the huge number of fail login attempts when you log into your Centos server? Want to find out who was the bad guy trying to crack your server login?

This post will walk you through how to exam SSH login log on your Centos server, find the IP addresses that initiated a large number of login attempts. and block these IP from further brute force attacks.

Follow the instruction below you can get a list all failed SSH logins and group them by the IP addresses.

Locate the Log Files

Fist, use CD command to locate the log file directory on your Centos server.

You will see a lot log files. The SSH login log files are those starting with secure, e.g. secure-20171224. Now we want to combine all SSH login files before we go over them.

Combine all SSL Log Files

Run the command below to combine them together to a new file.

Analyze Log

We have combined all SSH login log to a single file named merged-file. We can run some analysis now.

Run the command above, you will generate another file(named result) in which each row is an IP address that attempted to login and failed, along with how many times he tried, for example you will see results like below:

18 101.95.26.126
1 102.250.51.207
1 102.251.192.26
31 103.10.168.138
37 103.10.230.126
2 103.11.135.132
36 103.12.196.125
3 103.15.74.82
7 103.16.168.138
385 103.192.253.37
6 103.192.61.9
1 103.192.76.100

SSH brute force

Download the file, convert it to a spreadsheet, so you can do sorting by the number of attempts. Then you can use iptable or access.denied to block access from those IPs on your Centos server.