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Debian / Ubuntu

How to configure Postfix relayhost (smarthost) to send eMail using an external smptd

How do I configure Postfix MTA to send eMail using an external cloud-based SMTP server (with username: password) from a web server on Linux or Unix-like system? How do I configure an Ubuntu server and postfix as the relay server (smarthost)?
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Sysadmin because even developers need heroes!!!

cron Error: bad username; while reading /etc/cron.d file on Linux

I am getting the following error in my cron job log file /var/log/cron.log:
       Aug 22 01:59:01 server2 cron[7510]: Error: bad username; while reading /etc/cron.d/backups
I have job entry as follows to run a job at 00:50 every day for root user:
       50 0 * * * /etc/cron.d/backups
How do I fix this problem on Linux or Unix-like system?
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How to make disk image with dd on Linux or Unix

How do I create disk image using dd command? How do I perform disk cloning from a live Linux cd for backup or recovery purpose?
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How to create RAID 10 – Striped Mirror Vdev ZPool On Ubuntu Linux

How do I create zfs based RAID 10 (striped mirrored VDEVs) for my server as I need to do small random read I/O. How can I create striped 2 x 2 zfs mirrored pool on Ubuntu Linux 16.04 LTS server?
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How to setup a UFW firewall on Ubuntu 16.04 LTS server

How do I setup a firewall with UFW (uncomplicated firewall) on an Ubuntu Linux 16.04 LTS server to restrict traffic on my personal web-server that hosts my pictures and blogs for my family members?
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Linux how long a process has been running?

I‘m a new Linux system user. How do I check how long a process or pid has been running on my Ubuntu Linux server?
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How do I speed up my apt-get or apt command to download packages from multiple repos on a Ubuntu Linux 16.04 or 14.04 LTS server? How do I use apt-fast command on a Debian Linux server?
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How To Setup Bonded (bond0) and Bridged (br0) Networking On Ubuntu LTS Server

I want to setup KVM bridge with bonding on Ubuntu Linux 16.04 LTS server. I have total four Intel I350 Gigabit network connection (NICs). I would like bonding/enslaving eth0 through eth2 into one bonded interface called bond0 with 802.3ad dynamic link aggregation mode. How do I configure bridging and bonding with Ubuntu Server 16.04 LTS?
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Ubuntu setup a bonding device and enslave two real Ethernet devices

How do I setup a bonding device bond0 and enslave two real Ethernet (say eth0 and eth2) devices to it on Ubuntu Linux 140.04 or 16.04 LTS server? How can I create 802.3ad bonding mode (IEEE 802.3ad Dynamic link aggregation) on Ubuntu Linux 16.04 LTS server?
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How to determine Linux guest VM virtualization technology

I have a cloud-based virtual machine running Ubuntu and CentOS Linux server. It may or may not be virtualized. How do I determine what kind of virtualization technology (VMWARE/ KVM/ XEN/ VirtualBox/ Container/ lxc/Hyper-V etc.) a Linux guest system running on? How do I find out the virtualization type of a CentOS 7 Linux VPS?
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