An SSL Certificate is a text file with encrypted data that you install on your server so that you can secure/encrypt sensitive communications between your site and your customers. After you create a CSR (certificate signing request) and purchase a certificate, our Validation team validates and processes your certificate request. Once validated, we issue your  Full Article…

RSA encryption is a public-key encryption technology developed by RSA Data Security. The RSA algorithm is based on the difficulty in factoring very large numbers. Based on this principle, the RSA encryption algorithm uses prime factorization as the trap door for encryption. Deducing an RSA key, therefore, takes a huge amount of time and processing  Full Article…

Try arp -a to see your computer’s current arp table. It will show only those IP addresses your computer has interacted with. Output like this (obscured a little to hide MAC addresses on my network): $ arp -a ? (10.1.168.1) at xx:xx:9e:82:ab:f6 on en1 ifscope [ethernet] ? (10.1.168.16) at xx:xx:29:d3:17:8 on en1 ifscope [ethernet] ?  Full Article…

Using the OSI model, which layer has the responsibility of making sure that the packet gets where it is supposed to go? What is the subnet mask, network address and broadcast address for the following address: 123.65.47.62/22? What command is used to show all open ports and/or socket connections on a machine? What is NAT?  Full Article…

ps ax | wc -l | tr -d ” ” OR ps ax | wc -l | awk ‘{print $1}’ OR ps ax | wc -l | sed -e “s: ::g”. In each case, tr or awk or sed is used to remove the undesirable whitespace. Relative speed: any one of these variants takes about  Full Article…

If you want to know how much space the contents of the current directory take up, you can use something like the following: let TotalBytes=0 for Bytes in $(ls -l | grep “^-” | awk ‘{ print $5 }’) do let TotalBytes=$TotalBytes+$Bytes done # The if…fi’s give a more specific output in byte, kilobyte, megabyte,  Full Article…

List folders with file count: find -maxdepth 1 -type d | sort | while read -r dir; do n=$(find “$dir” -type f | wc -l); printf “%4d : %s\n” $n “$dir”; done List folders with non-zero file count: find -maxdepth 1 -type d | sort | while read -r dir; do n=$(find “$dir” -type f  Full Article…

To count the number of files in a directory, I typically use ls directory | wc -l   I found this: find DIR_NAME -type f | wc -l Explanation: -type f to include only files. | redirects find command’s standard output to wc command’s standard input. wc (short for word count) counts newlines, words and  Full Article…

this is one: ls -l . | egrep -c ‘^-‘ Note: ls -1 | wc -l Which means: ls: list files in dir -1: (that’s a ONE) only one entry per line. Change it to -1a if you want hidden files too | : pipe output onto… wc: “wordcount” -l: count lines.   Counting Files  Full Article…

By default the first user’s account is an administrative account, so if the UI is prompting you for a password it’s probably that person’s user password. If the user doesn’t remember their password you need to reset it. To do this you need to boot into recovery mode. Boot up the machine, and after the  Full Article…

The way on how you can reset a forgotten root password on a Linux system have not changed for many years. Resetting a root password on RHEL7 Linux system have not change much except that now we deal with SElinux and the system is now using systemd instead of init. Nevertheless, those who have already  Full Article…

starting with debian woody,redhat and suse to ubuntu . UPDATE:To recover a root password on REDHAT and CentOS visit a following guide on how to recover a root password on RHEL 7 Linux. UPDATE:To recover a root password on Ubuntu visit a following guide on how to recover a root password on Ubuntu 16.04 Xenial  Full Article…

Use below commands to know more about the mount points cat /etc/mtab df -h   Q. What is a network mount point? A network mount is a mount point which can access network file systems like NFS, Samba, FTP, SSH, etc.

Linux records information about when files were created and last modified as well as when it was last accessed. There is a cost associated with recording the last access time. ext2/ext3 file systems have an attribute that allows the super-user to mark individual files such that their last access time is not recorded. This may  Full Article…

As a process executes it changes state according to its circumstances. Unix processes have the following states: Running* : The process is either running or it is ready to run . Waiting* : The process is waiting for an event or for a resource. Stopped* : The process has been stopped, usually by receiving a signal. Zombie* : The  Full Article…

/var/log/* remote logging how would you set this up? syslog.conf remote crashdumps how would you set this up? netdump

/ # root filesystem. /boot # Contains kernel images. And if grub is bootloader it is contained here as well. /etc # Contains configuration files. /bin # Contains system binaries. /sbin # Contains secure system binaries /lib # Contains system library files /home # user directories /opt # generally used for optional packages /usr #  Full Article…

Good answers will mention some or all of the following: ssh Setting up password-less ssh for the machines, or assuming that they are already set up A command-line for loop which iterates over machines doing something Perl script also OK Stellar candidates will mention “xargs -P” which will allow them to run some commands in  Full Article…

System goes through POST ( Reads BIOS settings and initializes hardware ). System determines the primary boot device. System reads Master Boot Record of device. Depending on boot loader installed with either start Grub or LILO. Boot Loader determines default kernel image. Boot loader decompresses kernel image. Kernel loads modules for all the hardware and  Full Article…

Setup network on centos 7 let’s start, Type “nmcli d” command in your terminal for quick identification of Ethernet cards installed in your machine. Here we have 2 interfaces named “enp0s17” and “enp0s18” . it might be different in your case ( Eg: em1 or p4p1 ). GUI Mode Recommended for beginners Step 1 »  Full Article…

Dead-Lock is occurred in multiple users Computing Environment. As we know that there is Many Number of users those are going to perform their Transactions. Dead-Lock has occurred when two or More Users are requesting for data item or for a Resource of System for example two or more users Request for the Printers at  Full Article…

RAM: Read / Write memory, High Speed, Volatile Memory. ROM: Read only memory, Low Speed, Non Voliate Memory. 1. When power is lost or turned off, a ROM chip will keep the information stored on it. In contrast, a RAM chip is volatile and requires a constant source of power to retain information. 2. A  Full Article…

The exit-point from one network and entry-way into another network, often the router of the network.

Cache memory is a small high-speed memory. It is used for temporary storage of data & information between the main memory and the CPU (center processing unit). Thecache memory is only in RAM.

The TCP three-way handshake in Transmission Control Protocol (also called the TCP-handshake; three message handshake and/or SYN-SYN-ACK) is the method used by TCP set up a TCP/IP connection over an Internet Protocol based network. TCP’s three way handshaking technique is often referred to as “SYN-SYN-ACK” (or more accurately SYN, SYN-ACK, ACK) because there are three  Full Article…

The Bootstrap Protocol (BOOTP) is a computer networking protocol used in Internet Protocol networks to automatically assign an IP address to network devices from a configuration server. The BOOTP was originally defined in RFC 951. BOOTP was largely replaced by the more efficient Dynamic Host Configuration Protocol (DHCP), which has more options and flexibility. However,  Full Article…

How to disable IPTABLES ? ================== # service iptables save # service iptables stop # chkconfig iptables off How To clear IP rules in IPTABLES use below commands: ===================================== # iptables -F # iptables -X # iptables -t nat -F # iptables -t nat -X # iptables -t mangle -F # iptables -t mangle -X  Full Article…

1.What is yum  ? Answer: yum is “yellow update manager” which is a front end tool for package management. All the rpm commands activity can be carried out using yum command in automated way. Yum mechanism will automatically resolve the dependencies unlike rpm commands. 2.How to install packages using yum ? Answer:yum install package_name 3.How  Full Article…

1) What’s the command to stop Apache? kill the specific process that httpd is running under, or killall httpd. If you have apachectl installed, use apachectl stop. 2) How do you set up a virtual host in Apache? <VirtualHost www.amitmaheshwari.in> ServerAdmin admin@amitmaheshwari.in DocumentRoot /home/apache/share/htdocs/hostedsites ServerName www.amitmaheshwari.in ErrorLog /home/apache/logs/error/hostedsites/error_log TransferLog /home/apache/logs/access/hostedsites/access_log </VirtualHost> 3) What is mod_vhost_alias?  Full Article…

1. Create an SSH Key Use the ssh-keygen command to create an SSH key.  Accept all the defaults by pressing ENTER at every prompt.  You’ll want to leave the passphrase empty. linuxsvr01$ ssh-keygen Generating public/private rsa key pair. Enter file in which to save the key (/home/user/.ssh/id_rsa): Enter passphrase (empty for no passphrase): Enter same  Full Article…

DNS stand for Domain Name System. ## What is the main purpose of a DNS server? DNS servers are used to resolve FQDN hostnames into IP addresses and vice versa. ## What is the port no of dns ? 53. ## What is a Forward Lookup? Resolving Host Names to IP Addresses. ## What is  Full Article…

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  In order to help you understand the OSI Model, I am going to briefly describe how each layer functions in a Building Automation System framework: Physical Layer- This is the media you use to communicate (RS-485/Ethernet ect). Data Link Layer– This is the subnet communication, or for example, the communication of MS/TP on a  Full Article…

So I received a warning from our monitoring system on one of our boxes that the number of free inodes on a filesystem was getting low. df -i output shows this: Filesystem Inodes IUsed IFree IUse% Mounted on /dev/xvda1 524288 422613 101675 81% / As you can see, the root partition has 81% of its  Full Article…

One of our development servers went down today. Problems started with deployment script that claimed that claimed “No space left on device”, although partition was not nearly full. If you ever run into such trouble – most likely you have too many small or 0-sized files on your disk, and while you have enough disk  Full Article…

A TCP/IP subnet is a segment of a network where all of the computers on that segment can communicate with each other without having to go through a router.  The computers on the subnet will have IP addresses that are within a given range of addresses, and those addresses will all have the same network  Full Article…

If I am sending a 1 GB file through a 1 Gb/s LAN connection, from one computer to another, how much time will it take to transfer that file? In a 1 Gbps connection, 1 Gigabit will take 1 second. Since there are 8 bits in a byte, 1 Gigabyte will take 8 times longer.  Full Article…

The following steps will show configuration of static IP address in CentOS machine. Files needed for network configuration are under /etc/sysconfig/network-scripts. So open the file with editor like nano or vi. Here I will use nano editor. After you start your server running CentOS enter root user credentials and get in. Type the command, #  Full Article…

Hypervisors use a thin layer of code in software or firmware to allocate resources in real-time. You can think of the hypervisor as the traffic cop that controls I/O and memory management. Type 1 hypervisors run directly on the system hardware. They are often referred to as a “native” or “bare metal” or “embedded” hypervisors  Full Article…

To find out about memory use, we can look at a proc file, MemInfo. If we look at the beginning of the file, the head of it, we see it reports MemTotal. So this particular box has, like, 16 gig. Incidentally, this is the memory available when you boot Linux, you could tell it how  Full Article…

So, here’s the plan: Set up a PXE environment. Find the minimal kernel config that exhibits the issue. Create a custom initrd containing all the tools needed to detect whether an issue is there. Create a script that can be reliably used by git bisect to make it all run automatically. PXE PXE is a  Full Article…

What are all the components in a PC or Server? PC: chassi, system board, psu, cpu, ram, hdd, fans, cables, graphics card, dvd, monitor, keyboard/mouse Server: same with deduction of a extra graphics card (is one on the system board), and addition of hdd controller, possibly backplane, no cd/dvd, extra nic, double cpu, ram, psu,  Full Article…

The system calls used for low-level process creation are execlp() and execvp(). The execlp call overlays the existing program with the new one , runs that and exits. The original program gets back control only when an error occurs. execlp(path,file_name,arguments..); //last argument must be NULL A variant of execlp called execvp is used when the  Full Article…

When you enter ‘ls’  command to look at the contents of your current working directory,   UNIX does a series of things to create an environment for ls and the run it: The shell has UNIX perform a fork. This creates a new process that the shell will use to run the ls program. The  Full Article…

It contains all the information of the users who log into the system. It contains a list of the system’s accounts, giving for each account some useful information like user ID, group ID, home directory, shell, etc. It should have general read permission as many utilities, like ls use it to map user IDs to  Full Article…

Swapping : Whole process is moved from the swap device to the main memory for execution. Process size must be less than or equal to the available main memory. It is easier to implementation and overhead to the system. Swapping systems does not handle the  memory more flexibly as compared to the paging systems.   Paging : Only  Full Article…

  The most common reason to put a process in the background is to allow you to do something else interactively without waiting for the process to complete. At the end of the command you add the special background symbol, “&”. This symbol tells your shell to execute the given command in the background.  Example: # cp  Full Article…

 # du –ah / | sort –n –r | head –n 1 Option Explanations :- du – estimate file space usage -a – write counts for all files, not just directories -h – print sizes in human readable format (eg. 1K 234M 2G) sort – sort lines of text files -n – compare according to  Full Article…

syslogd is  responsible for tracking system information and save it to the desired log files. It provides two system utilities which provide system logging and kernel message trapping. Internet and UNIX domain sockets support enable this utility package to support both local and remote logging.   Every logged message contains at least a time and  Full Article…

The article below will cover the basics of permissions and ownership for linux servers and how to change both of them. To start off we’ll create a file to work with. Creating a new file can be done with the completed with the ‘touch’ command. For example, say we want to create a new file  Full Article…

IPTables : Opening ports in IPTables is a bit harder than Firewalld or UFW, but it is simple once you get the hang of it. Whenever you make any changes within IPTables, you’ll want to save the changes and reload the firewall, or the changes will be lost next time the firewall is reloaded or  Full Article…

Logical Volume Management (AKA LVM) is a powerful, robust mechanism for managing storage space. How LVM works In LVM, there are several layers, each builds on top of the other: PV[s] (Physical Volumes) -> VG[s] (Volume Groups) -> LV[s] (Logical Volumes) -> Filesystems. Logical Volumes are allocated/extended within the boundaries of their underlying storage pool  Full Article…

1.Is it possible to increase the logical volume on fly ? Answer: Yes.We can increase the logical volume without umount it. 2.How to reduce the logical volume ? is it possible to reduce on fly ? Answer: No.You can’t reduce the logical volume on fly. Here is the steps to reduce the logical volume on  Full Article…

Q:1 What is the default port & configuration file of SSH Server ? Ans: 22 is default port  for ssh and  ‘/etc/ssh/sshd_config’ is the configuration file. Q:2 How to change the default ssh port in linux ? Ans: To change the port , first edit the file ‘ /etc/ssh/sshd_config ‘ , change the  vaule of  Full Article…

Rsync allows you to synchronize directories locally or between two servers. Rsync determines which files are different or new between two locations and then synchronizes the directories. Rsync can be used to copy folders or entire directories. In my examples I use the following Rsync command line options. The -a option enables archive mode which  Full Article…

Open the /etc/sysconfig/network file with your favorite text editor. Modify the HOSTNAME= value to match your FQDN host name. # nano /etc/sysconfig/network HOSTNAME=myserver.domain.com Change the host that is associated to your main IP address for your server, this is for internal networking (found at /etc/hosts): nano /etc/hosts 192.xx.xx.xx myserver.domain.com Hostname Command Line Change The ‘hostname’  Full Article…

When making your Linux server more secure, you are going to want to look at four areas of the server: The SSH configuration IPTables Configuration (Software Firewall) The logs Applications .This guide assumes you know how to log into your server using SSH. If you do not know how to do this, please first read  Full Article…

creates a 1 GB swap partition for new virtual machines by default. For most users, this is plenty of swap space. However, different users may have differing needs. If your needs require a different amount of swap space, this guide shows you how to set up a custom sized swap space. First Steps Codero configures  Full Article…

Low-memory Linux virtual machines (less than 4GB RAM) can be cost-effective means for running web applications or hosting websites. However, sometimes performance can be constrained on such VMs. Presented below are a few suggestions for maximizing performance on low-memory Linux VMs. Kernel tuning We will use the ´sysctl´ program to tune a couple of Linux  Full Article…

du -chs command To locate which directories may be using an excessive amount of disk space, you can find them by executing the du -chs command as shown.  This will show how much disk space is used by each subdirectory. Note: Make sure you execute this command as root! Plesk example # du -chs /var/*  Full Article…

Stop the MySQL process # service mysqld stop Once MySQL has stopped, restart it with the –skip-grant-tables option # mysqld_safe –skip-grant-tables & or edit your /etc/my.cnf file to add the line skip-grant-tables Connect to MySQL using the root user. mysql -u root Once logged in, you should see the following prompt: mysql> Enter the following  Full Article…

First, make a backup of the /etc/network/interfaces file. cp /etc/network/interfaces /root/interfaces.bak Edit the /etc/network/interfaces file. vi /etc/network/interfaces Add a section for as many IP addresses as you are adding. auto eth0:0 iface eth0:0 inet static address xx.xx.xx.xx netmask 255.255.255.0 Fill in the address with your new IP address. Increment each new IP address interface by  Full Article…

Adding an IP address to a CentOS server is very easy. Go to the network configuration directory /etc/sysconfig/network-scripts Create a file with the name ifcfg-eth0:1 (This file increments, so if you already have several IP addresses you need to add the next increment, such as ifcfg-eth0:3 for the 4th IP) Paste the following contents into  Full Article…

MySQL, and databasing at large, is primarily meant for the storage and retrieval of large amounts of data, yet the default configuration file allocates very little memory to the MySQL service. When MySQL is afforded enough memory, much of your data can be stored in memory. The more data that is stored in MySQL’s memory,  Full Article…

Log In Log into your cloud instance as root using SSH.   Verify upgraded size You can verify the size of the drive had been upgraded by running fdisk. Notice: If you see this output, you are using a pre-LVM Codero Cloud instance. Notice: If you see this output, you are using a LVM Codero  Full Article…

Check to see how many drives are installed: You can do this using the fdisk command. [root@default]# fdisk -l | grep ‘^Disk You should see output similar to the following: Disk /dev/sda: 251.0 GB, 251000193024 bytes Disk /dev/sdb: 251.0 GB, 251000193024 bytes   Mount the new disk using the mount command: First, you’ll need to  Full Article…

Getting Started: Check to see how many drives are installed: You can do this using the fdisk command.  [root@default]# fdisk -l | grep ‘^Disk’ You should output similar to the following: Disk /dev/sda: 251.0 GB, 251000193024 bytes Disk /dev/sdb: 251.0 GB, 251000193024 bytes A device name refers to the entire hard disk. For more information see Linux partition naming  Full Article…

Packet injection (also known as forging packets or spoofing packets) is a computer networking term that refers to the process of interfering with an established network connection, by means of constructing packets to appear as if they are part of the normal communication stream. The packet injection process allows an unknown third party to disrupt  Full Article…

Look up data on /dev/sda1: topher@crucible:~$ sudo blkid /dev/sda1 /dev/sda1: UUID=”727cac18-044b-4504-87f1-a5aefa774bda” TYPE=”ext3″ Show UUID data for all partitions: topher@crucible:~$ sudo blkid /dev/sda1: UUID=”727cac18-044b-4504-87f1-a5aefa774bda” TYPE=”ext3″ /dev/sdb: UUID=”467c4aa9-963d-4467-8cd0-d58caaacaff4″ TYPE=”ext3″ Show UUID data for all partitions in easier to read format: (Note: in newer releases, blkid -L has a different meaning, and blkid -o list should be used  Full Article…

Port TCP UDP Description Status 0 N/A N/A In programming APIs (not in communication between hosts), requests a system-allocated (dynamic) port[3][4] N/A 0 UDP Reserved Official 1 TCP UDP TCP Port Service Multiplexer (TCPMUX) Official 2 TCP UDP CompressNET[5] Management Utility[6] Official 3 TCP UDP CompressNET[5] Compression Process[7] Official 4 TCP UDP Unassigned Official 5  Full Article…

a single config file control process ks.conf use anaconda-ks.cfg  in /root # cp anaconda-ks.cfg /var/ftp/pub/ # chmod 755 /var/ftp/pub/anaconda-ks.cfg use /csconfig GUI put ks.conf on teh network type  “linux=nfs:192.123.12.3:/ks/ks.conf”    <— at boot prompt PXE works with Network Interface Card (NIC) of the system by making it function like a boot device. The PXE-enabled NIC of  Full Article…

– ifconfig eth0:1 192.168.123.10 – ifconfig eth0:sub1 192.168.123.10   Add a second temporary IP address Using ifconfig If you want to add a secondary IP address to a NIC already in use in Linux, and have that change only temporary. Enter this command: ifconfig [nic]:0 [IP-Address] netmask [mask] up An example is shown below ifconfig  Full Article…

LVM terms and concepts

Arch Add the following addressing to the interface’s configuration. /etc/systemd/network/05-eth0.network 1 2 3 4 5 6 7 8 9 10 11 12 13 14 [Match] Name=eth0 [Network] Gateway=198.51.100.1 # Your primary public IP address Address=198.51.100.2/24 # To add a second public IP address: Address=198.51.100.3/24 #To add a private IP address: Address=192.168.133.234/17 Static IP addresses can  Full Article…

#!/bin/bash ipvariable=$(wget http://ipecho.net/plain -O – -q); echo “Today the location is http://$ipvariable:123456/foldertheyreach” | mail -s “From your friendly cloud service provider” user1@someemail.com, user2@ect.com

Using dig with OpenDNS as resolver: dig +short myip.opendns.com @resolver1.opendns.com Perhaps alias it in your bashrc so it’s easy to remember alias wanip=’dig +short myip.opendns.com @resolver1.opendns.com’ Responds with a plain ip address: $ wanip 12.100.14.123     curl -s http://whatismijnip.nl |cut -d ” ” -f 5 curl -s icanhazip.com The fastest method using DNS: dig  Full Article…

Jumbo frames : Ethernet frames are normally 1.500 bytes(payload) but the Jumbo Frame spec allows MTUs of 9.000 bytes Jumbo frames are used on local area networks that support at least 1 Gbps and can be as large as 9,000 bytes. Because jumbo frames are not defined in the IEEE 802.3 specifications for Ethernet, vendor  Full Article…

The two most popular storage system technologies are file level storage and block level storage. File level storage is seen and deployed in Network Attached Storage (NAS) systems. Block level storage is seen and deployed in Storage Area Network (SAN) storage. In the article below, we will explain the major differences between file level storage  Full Article…

Nas Network Attached Storage – File level access to storage using CIFS or NFS the cost effective option Storage Area Network SAn Block Level access to storage you can easily virtualize iSCSI     What is a file storage? File storage, also called file-level storage, or file-based storage is a type of storage that stores  Full Article…

Virtual Extensible LAN (VXLAN) is a proposed encapsulation protocol for running an overlay network on existing Layer 3 infrastructure. An overlay network is a virtual network that is built on top of existing network Layer 2 and Layer 3 technologies to support elastic compute architectures. The primary goal of VXLAN is to extend the virtual  Full Article…