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How to force users to use secure passwords on Ubuntu/Debian Linux

My Linux shell user can modify their password using the passwd command. How can I force users to choose the secure password that will prevent users from using stupid passwords like “abc123”, “password”, “123456” and so on? How do I setup password quality requirements on my Debian or Ubuntu Linux server?
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Sysadmin because even developers need heroes!!!

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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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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Ubuntu 16.04 Create a cron.log File To Log crontab Logs

I am a new Ubuntu Linux 16.04 user. How do I verify that my cron job is executing? I am unable to find /var/log/cron.log file. Where is the cron log file on Ubuntu 16.04 LTS server?
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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 see CPU temperature on CentOS 7 and RedHat Enterprise Linux 7

I am a new sysadmin of CentOS 7 server. How do I get my CPU temperature Information on CentOS Linux 7 or Red Hat Enterprise Linux 7 server?
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PHP-fpm Too Many Open Files 24 Error (set open file descriptor limit)

I am getting the following error in my /var/log/php7.0-fpm.log file:
        “ERROR: failed to prepare the stderr pipe: Too many open files (24)
How do I fix this problem?
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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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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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