Category Archives: Linux

You got to love Linux. Not only that it is free, but it is also very strong, stable, and widely used.

Block Countries by IP on Debian Trixie with nftables and xtables-addons

Posted on May 11, 2026 by ronaldpringadi

Debian Trixie uses nftables as its default firewall. If you’re used to iptables, the commands still work — but they go through an iptables-nft compatibility shim that translates them to nftables rules under the hood. For country-based IP blocking, the … Continue reading →

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List open or listening ports

Posted on March 29, 2019 by ronaldpringadi

You started a service, you can’t tell whether it actually bound to its port, and you want to see what’s listening — or you want to find out which process is squatting on port 8080. Two one-liners, two operating systems: … Continue reading →

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CentOS 6 repo Settings

Posted on March 2, 2018 by ronaldpringadi

To fix repo settings in CentOS 6 1. make sure there is no proxy or funny settings in vi /etc/yum.conf 2. There are a couple of files within /etc/yum.repos.d/. Make sure the url are correct (accessible) and enabled=1 ll /etc/yum.repos.d/ … Continue reading →

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Show Linux Partition Tree Mountpoint and If SSD

Posted on June 27, 2017 by ronaldpringadi

1lsblk -o TYPE,NAME,KNAME,UUID,MOUNTPOINT,SIZE,ROTA

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SELinux directory permission

Posted on November 8, 2016 by ronaldpringadi

To check SELinux directory permission you need to -z for example 1ls -Z /var/www/html If something is incorrect you can re-adjust some of the directory permission: 1chcon -R -t httpd_sys_content_t /var/www/html

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RedHat / Centos Firewall

Posted on November 8, 2016 by ronaldpringadi

To add an exception to firewall In RedHat/CentOS 6 12345iptables –line -vnL iptables -A INPUT -p tcp –dport 80 -m state –state NEW,ESTABLISHED -j ACCEPT iptables -A INPUT -p tcp -s 192.168.0.0/16 -j ACCEPT iptables -D INPUT -p tcp -s … Continue reading →

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Bash string comparison

Posted on September 6, 2016 by ronaldpringadi

1234567891011121314151617181920212223242526272829303132333435363738394041424344454647484950515253545556575859606162636465#!/bin/bash function test(){ echo "" echo "TEST $1" echo "VAR_1: $VAR_1 VAR_2: $VAR_2 " if [ "$VAR_1" = "false" ]; then echo " VAR_1 is false"; fi if [ "$VAR_2" = "false" ]; then echo " VAR_2 is false"; fi … Continue reading →

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VirtualBox – Imporving usability on guest OS

Posted on May 17, 2016 by ronaldpringadi

GUEST OS: Centos 6.7 final HOST OS: Windows 7 Virtualbox version: 5.0.4 1yum install gcc kernel-devel kernel-headers dkms make bzip2 perl

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RedHat or CentOS 6 iptables adding an open port

Posted on May 16, 2016 by ronaldpringadi

iptables –line -vnL iptables -I INPUT 5 -p tcp –dport 80 -m state –state NEW,ESTABLISHED -j ACCEPT service iptables save

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Crontab header

Posted on February 1, 2016 by ronaldpringadi

123456# minute (0-59), # |      hour (0-23), # |      |       day of the month (1-31), # |      |       |       month of the year (1-12), # … Continue reading →

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