#Unix

Preface Virtualization My Scenario Process Isolation Further reading Preface How can I make sure that,my virtual server is isolated from the neighbour in same compute host ? Almost all the cloud admins faced this question at least once in their career time. Customer is worrying about the privacy, security of their data. So, question is quiet natural. They completely trust you, but still question remains. How I am isolated from the neary by guests. [Read More]

It happend, What now ? Get into battlefield Monitoring Cell Engineering Cell Customer success Cell Administrative Cell You brought it back Post incident measures It happend, What now ? Its a nightmare for a every cloud provider. Even you take all the measures to prevent, it could be happen. Its called Disaster. You are serving a lot of customers, you have to protect their interests. Because they are also a service provider to their customers. [Read More]

Preface Some countries are blacklisted in ecommerce area due to spam flooding and DoS attacks. Its not difficult to find the root of an IP address. So the following script will block country based traffic in to your web server. The data will be updated in every day through a cronjob. You need to visit this SITE to download the zone file for which country you need to block. mkdir -p /opt/scripts [Read More]

Preface A major problem facing by mail server admin is DOS (Deniel Of Service) attack. Hackers will try to mess up with the most popular ports of a UNIX/LINUX machines. We can prevent this my writing an IPTABLE rule in the server. The working is ,if some one is trying make connection continuously through a specified port the rule will block the IPADDRESS permanently. Here I am stating the securing of PORT 25 (SMTP) here you can use your own [Read More]

How to Test Write Speed How to Test Read Speed How to Test Write Speed sync; dd if=/dev/zero of=tempfile bs=1M count=1024; sync 1024+0 records in 1024+0 records out 1073741824 bytes (1.1 GB) copied, 3.28696 s, 327 MB/s How to Test Read Speed dd if=tempfile of=/dev/null bs=1M count=1024 1024+0 records in 1024+0 records out 1073741824 bytes (1.1 GB) copied, 0.159273 s, 6.7 GB/s Clear the Cache and Run again sudo /sbin/sysctl -w vm. [Read More]

What is an EXT4 The ext4 file system is a scalable extension of the ext3 file system. It can support files and file systems up to 16 terabytes in size. It also supports an unlimited number of sub-directories (the ext3 file system only supports up to 32,000), though once the link count exceeds 65,000 it resets to 1 and is no longer increased. Ext4 uses extents (as opposed to the traditional block mapping scheme used by ext2 and ext3), which improves performance when using large files and reduces metadata overhead for large files. [Read More]

Preface grep command syntax redirect output using pipe Regex patterns using -E Preface One of the most useful and versatile commands in a Linux terminal environment is the “grep” command. The name “grep” stands for “global regular expression print”. This means that grep can be used to see if the input it receives matches a specified pattern. This seemingly trivial program is extremely powerful when used correctly. Its ability to sort input based on complex rules makes it a popular link in many command chains. [Read More]

Meltdown is a chip-level security vulnerability that breaks the most fundamental isolation between user programs and the operating system. It allows a program to access the operating system kernel’s and other programs’ private memory areas, and possibly steal sensitive data, such as passwords, crypto-keys and other secrets. spectre-meltdown-checker is a simple shell script to check if your Linux system is vulnerable against the 3 “speculative execution” CVEs (Common Vulnerabilities and Exposures) that were made public early this year. [Read More]

Preface Head basic usage n number of lines Specific number of bytes only Preface There are several commands and programs provided by Linux for viewing the contents of file. Working with files is one of the daunting task, most of the computer users be it newbie, regular user, advanced user, developer, admin, etc performs. Working with files effectively and efficiently is an art. Today, in this article we will be discussing the most popular command called head. [Read More]