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Hi. I have set up a POSTFIX server in an AWS EC2 instance. If I try to send emails between local users using Sendmail, it works. However, if I try with an external account (gmail for example), it doesn't work. Command: echo "test email" | sendmail [email protected] POSTFIX Log...

Hi! I have set up a bind9 local DNS with rescursion turned off. From the DNS server, if I query google.es using DIG it returns: ;; WARNING: recursion requested but not available However, if I use HOST, it works: google.es has address 216.58.215.131 Same happens with NSLOOKUP nslookup...

Hi. I have a Debian Server VM box and the network cards work perfectly. However, I don't know which service is managing the network interfaces and how to change the way they work. The box uses NetworkManager and I can see some logs via journalctl. The thing is the file...

Hi everyone. I have set up my home wifi connection with NetworkManager GUI. Everything works fine with DHCP on and all gateway, DNS parameters are correctly obtained fron my router. I also have Netplan, with a yaml file stating that my wifi adapter should not use DHCP, and it's using...

Hi, I have an strange issue with bind9 which I can't solve. I have defined my own and local domain, domain.local. In the forward resolution file I have the following entries: domain.local. IN A 172.17.70.1 www IN CNAME domain.local. nslookup resolves domain.local and...

Hi! I have seen many ways to manage services in Ubuntu. Such as Systemctl - sysctl - systemd - /etc/init.d scripts and so on. Some of them seem to work always, whereas some not. ¿What is the difference among them all? Thanks!

Hi! I'm struggling to configure a quite simple network using Debian. I can't see the difference between using the following commands to set the networking parameters. ip ifconfig netplan /etc/network/interfaces file When to use one or another? Why so many tools for the same purpose? Does any...

Hi. I have been working with crontab to schedule jobs. I usually run crontab -l (to list the jobs) or crontab -e (to edit them). Always bearing in mind each user. I also have found the following directories: /etc/anacrontab /etc/cron.d /etc/cron.daily /etc/cron.hourly /etc/cron.monthly...

Hi! I have used CERTBOT and successfully get the SSL certificates. However, I don't understand the purpose and difference between these 2 files: /etc/letsencrypt/live/domain.com/fullchain.pem /etc/letsencrypt/live/domain.com/privkey.pem What does each one do? Thanks!

Hi! I have been using SSH for a long time, and I do know the purpose of ssh-copy-id command. If I copy the pubfile contents and paste it into the authorised_keys file on the target server, that's OK, because I already have access to the target server, and there are not security concerns...

Hi! I have a Dell XPS Laptop with Ubuntu 20.04 installed. Recently, the wifi adapter stopped working all of a sudden, without any update. The network manager shows "No Wifi Adapter available". systemctl status networkmanager shows: device (wlp59s0): state change: unmanaged -> unavailable...

Hi everyone. I have a doubt. If I point my browser to an specific web (let's say facebook.com), it works. So far so good. Now I try to resolve its IP by command line with dig or host commands. dig returns the following: facebook.com. 300 IN A 31.13.83.36 Now, if I point my...

Hi! I have created a public-private keypair with ssh-keygen and I have both id_rsa and id_rsa.pub. I'm trying to encrypt/decrypt files with openssl. If I cypher the file with cat plain_file | openssl rsautl -encrypt -pubin -inkey /tmp/id_rsa.pub > /tmp/encrypted.txt it works. I try to...

Hi! I made a mistake writing an URL, and instead of writing domain.org, i typed domain.es. My browser pointed to my localhost, showing the Apache welcome page, since I have apache2 installed. If I run dig or nslookup to domain.es, I get: ;; ANSWER SECTION: domain.es. 7056 IN A...

Hi. I'm trying to find out which DNS I'm querying. With dig: ;; SERVER: 127.0.0.53#53(127.0.0.53) cat /etc/resolv.conf nameserver 127.0.0.53 However, if I go to my settings, or I run resolvectl status , I get 172.20.18.1 Which one is correct and why am I getting 2 different results...

Hi! I have created a filesystem inside a regular file: 1. Created a dummy 2GB file. 2. Created the partition with fdisk <file> 3. Formatted it with mkfs.ext4 <file> 4. Checked it with file <file>. I got the UUID. 5. Added it to /etc/fstab starting with the UUID. 6. Remounted all with mount -a...

Hi! I want to develop a relative small project in an educational environment. Let's say I want to make my own "mini Netflix". What I want to achieve is how to setup a media streaming server setup to deliver audio/video files to clients via streaming. Nothing very complex. Just a PoC to show it...

Hello. I have a problem while trying to run an Android emulator in an Ubuntu Virtual Machine. I'm using VirtualBox7 as hypervisor. When I run the emulator command, the android emulator launches, but I see nothing but a black screen. I got a warning popup from VirtualBox saying that Nested...

Hi. I'm trying to install a .deb package in Ubuntu 20.04. sudo dpkg -i remarkable_1.87_all.deb I have dependency problems: dpkg: dependency problems prevent configuration of remarkable: I have read that this can be solved with sudo apt-get -f install, but the only thing I get is this...

Hi everyone. I have downloaded the Android tools and I'm running some tests via CLI. I create 2 Android emulators with avdmanager and then I connect to them via adb. If I want to see the list of emulators, I get: avdmanager list avd Available Android Virtual Devices: Name: Android1...