Various public services portals accept files in electronic form of a strictly limited size. The usual requirement is a file size less than 5 MB. But many PDF files have a larger size due to the fact that the PDF format has recently been used for storing scanned documents. This message shows two ways to reduce the size of PDF files.

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The FT8 digital mode has gained incredible popularity and recognition around the world. Radio amateurs want to use it not only for long-distance DX QSOs on short waves, but also in competitions, including on ultra-short waves 144 and 432 MHz. The WSJT-X program provides an operating mode for European competitions using FT8 modulation.

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When the RAM runs out, the computer becomes very slow as it accesses the swap file on the hard drive. To solve this problem, the zswap module was invented. By default, it is disabled in the Linux operating system, but you can enable it.

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For diagnostic purposes, I have boot-time messages enabled in /etc/default/grub (line GRUB_CMDLINE_LINUX=""
).
When starting a computer running Linux Mint 19.2, errors like FAILED Failed to start AppArmor are visible. The problem started after reinstalling the MySQL service to manage relational databases. The solution to the "Failed to start AppArmor" problem is given below...

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In a TP-Link network router ("router") with OpenWrt firmware, it was necessary to block the MAC address of the network device on the local network so that the device would not have access to the Internet.

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Task: upload photos via Wi-Fi from a smartphone to a personal computer running Linux.

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In a large network with DHCP enabled, intrusions sometimes occur - third-party connections.
They need to be tracked. It is convenient to take pictures of the network - before and after.
In the article I talk about two ways to compile a list of computers (a network snapshot) - using nmap and arp-scan.

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To search for rare countries or simply monitor activity on bands, DX clusters operating via the Telnet protocol are traditionally used. The advantage is low traffic consumption and low system requirements. The disadvantage is control using console commands and the lack of a graphical user interface. I found a successful solution that combines the advantages of a Telnet cluster and a graphical shell - a program from VE7CC.

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APRS over TCP-IP (over the Internet) is very easy to set up.

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The system time zone is selected when installing the distribution. In the future, you can configure time synchronization (NTP protocol) for more accurate time and organize the display of information about other time zones. For example, when it is morning in Moscow, it is deep night in the central part of the United States. This article is about how to improve time synchronization, set the time zone and display the time of other time zones on the screen.

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