This guide assumes you have a working Postfix server and want it to sign with DKIM.
There are a few things we have to understand to make all of this work though, which require you to be familiar with DNS as well.
1.) Install OpenDKIM
apt install opendkim
systemctl enable opendkim
2.) Edit /etc/opendkim.conf
Syslog yes
SyslogSuccess yes
Mode&nbs........
Some people find it less than intuitive to do on DNSMasq and by default DNSMasq is available on 0.0.0.0 which could even be your LAN or Public IP.
Active Internet connections (servers and established)
Proto Recv-Q Send-Q Local Address Foreign Address State PID/Program name
tcp ........
If you are using a hypervisor to test Proxmox (eg. Vbox) then changing the video card/display adapter can fix it.
For example VboxSVGA causes the issue but switching to VMSVGA fixes it.
For example VboxSVGA causes the issue but switching to VMSVGA fixes it.
........
If you are running a local DNS server like named/bind and don't want to use the ISPsupplied DNS servers that are announced via a DHCP request (using dhclient) then the solution is simple.
The reason should be obvious, but normally running your own DNS server will provide a more reliable, and fast DNS response and you won't have to worry about filtering as much (unless your upstream filters or proxies outgoing DNS requests).
Edit /etc/dhcp/dhclient.conf........
If you get this error, it is often because you have configured Apache with modules that weren't actually installed. Eg. you try to load the PHPmodule but didn't actually install the apache2 php module, so the server can't start. In general, this error can often be caused by issues with problematic modules and/or Apache being configured for modules that have not actually be installed (eg. libapache2-mod-php) is missing.
The above results in this less than obv........
You'll notice that /etc/resolv.conf contains dire warners on most Linux Desktops.
# This file is managed by man:systemd-resolved(8). Do not edit.
#
# This is a dynamic resolv.conf file for connecting local clients to the
# internal DNS stub resolver of systemd-resolved. This file lists all
# configured search domains.
#
# Run "resolvectl status" to see details about the uplink DNS servers
# currently in use........
Virtualbox is a very powerful tool, but for some use cases it is less than optimal.
Say you are in a work, lab or other environment where you are not alone on the physical network and there could be overlap of IPs, but you need all of your VMs to be contactable from your host, VMs need to communicate with each other, and VMs need internet.
NAT Network will give you VM to VM communication and internet, however, it is buggy and unstable. It also doesn't allow host to VM co........
Have you checked your router/firewall logs and disconcertingly see connections to an unknown IP207.246.119.209:3478 from your Grandstream VOIPphones?
You're not alone and the Grandstream forums have discussed this issue.
However, even their own staff d........
Just use apt-cache policy to find the repo of a package:
apt-cache policy lxd
lxd:
Installed: 3.0.3-0ubuntu1~18.04.2
Candidate: 3.0.3-0ubuntu1~18.04.2
Version table:
*** 3.0.3-0ubuntu1~18.04.2 500
500 http://archive.ubuntu.com/ubuntu bionic-updates/main amd64 Packages
&nb........
freshclam
ClamAV update process started at Sun Mar 20 00:30:50 2022
WARNING: Your ClamAV installation is OUTDATED!
WARNING: Local version: 0.100.3 Recommended version: 0.103.5
DON'T PANIC! Read https://www.clamav.net/documents/upgrading-clamav
main.cld is up to date (version: 62, sigs: 6647427, f-level: 90, builder: sigmgr)
WARNING: getpatch: Can't download daily-26337.cdiff from db.local.clamav.net
WARNING:........
There is a random bug that sometimes occurs with Vbox NAT mode DNS, although it has never happened in the past and Vbox was working fine until recently.
The symptom is that you can see it does get an IP+ DNS from the Vbox NAT DHCP.
Below we use resolvectl dns and verify the DNS server is set to 10.0.2.3 which is the DNS from Vbox NAT. We can ping it but it does not respond to any DNS requests when we use dig @10.0.2.3 realtechtalk.com........
The Best Docker Tutorial for Beginners
We quickly explain the basic Docker concepts and show you how to do the most common tasks from starting your first container, to making custom images, a Docker Swarm Cluster Tutorial, docker compose and Docker buildfiles.........
How To Install Ceph
If you stopped an install of Ceph midway you will need to manually restart it with "pveceph install"
Remember that your VM needs to have working internet (gateway) and DNS in order to connect to the apt repo to download all of the packages that Ceph requires.
Remember to repeat these steps for each node that you want Ceph on.
........
Kubernetes Easy Beginners Tutorial/Architecture Guide
Kubernetes is known as container orchestration and we should start at explaining the container part of it.
A Container is what runs the actual application and based on an Image, and are more comparable to something like an LXC Container, Virtuozzo/OpenVZ using the Linux Kernel Namespaces feature. Containers run these images as independent, isolated operating environments under the O........
Just a quick note and warning is that if you are testing to see if EFIPXE booting works on a VM, MAKE SURE it actually works. For example Iinitially tested using my Distro's QEMU 2.5+dfsg-5ubuntu10.46 and ovmf BIOS firmware (OVMF supports EFI). However, I found on old versions of QEMU (like 2.5), EFIbooting with GRUB NEVER works so it may appear that you have made a mistake when everything is fine when you boot a physi........
Many people may not be aware that you can turn commodity hardware into a Mikrotik OS and there are various options which is "CHR" (Cloud Hosted Router) which is a VMimage meant for Virtualization only (seriously, I've tried to dd the image to a physical server and it just crashed as it does not contain any drivers for physical).
One note as well if you are trying to do a baremetal install you may get an error "Error Loading Operating System" or........
The below appears at first to be a bad mirror DNS error, but if you've ruled that out you just need to clear your broken yum cache and things will be good.
yum update
Loaded plugins: fastestmirror
Loading mirror speeds from cached hostfile
* base: centos.01link.hk
* extras: centos.01link.hk
* updates: centos.01link.hk
http://mirror.worria.com/centos/7.8.2003/os/x86_64/repodata/repomd.xml: [Errno 14] HTTP Error 404 - Not........
When authentication times out that is one thing, but when it just fails like below Asterisk by default will not re-register until you the admin reload the sip or asterisk server:
voipserver*CLI> sip show registry
Host dnsmgr Username Refresh State&........
Mar 22 13:46:14 box named[31767]: validating @0x7f51bc001550: . DNSKEY: unable to find a DNSKEY which verifies the DNSKEY RRset and also matches a trusted key for '.'
Mar 22 13:46:14 box named[31767]: validating @0x7f51bc001550: . DNSKEY: please check the 'trusted-keys' for '.' in named.conf.
Mar 22 13:46:14 box named[31767]: error (broken trust chain) resolving './NS/IN': 192.36.148.17#53
One possibility is sometimes that your time is ou........
By default bind will not respond to outside queries for security reasons.
In most distributions you will find the default in /etc/named.conf looks like this at the top under options:
listen-on port 53 { 127.0.0.1; };
listen-on-v6 port 53 { ::1; };
directory "/var/named";........
The strange thing is that usually the first install or two will work on any new machine but then it suddenly won't. I had this experience on QEMU 2.13 on a different machine. There is something finicky or buggy about the CUCM installer even when choosing the same virtual hardware specs.
qemu-kvm command:
/usr/libexec/qemu-kvm -version
QEMU PC emulator version 0.12.1 (qemu-kvm-0.12.1.2-2.506.el6_10.1), Copyright (c) 2003-2008 Fabrice Bellard
........
Just find the relevant file in /etc/NetworkManager/system-connections
sudo vi /etc/NetworkManager/system-connections/Wired connection 1
[802-3-ethernet]
duplex=full
mac-address=00:00:00:FE:FE:FE
[connection]
id=Wired connection 1
type=802-3-ethernet
timestamp=1532403341
[ipv6]
method=ignore
[ipv4]
method=manual........
Do you hate it when your ISPhas old cached records because of a high TTLon the DNS record of the relevant domain? In plain English this means you often can't connect to a site or service because your ISP's DNS servers haven't gotten word of the new IP address (probably because they haven't checked). There are also some that are notorious for ignoring TTL and not updating records for days!
But if you are lucky and smart enough to have your own Linux based DNS se........
First we need to create dhclient.conf if it doesn't exist or edit it:
vi /etc/dhclient/dhclient.conf
#add this line at the top add the IPs as commas they will be the highest priority nameservers and whatever your ISP gives you will be used after these one (good for DNS backup)
prepend domain-name-servers 127.0.0.1,10.10.25.8;
After you restart your network or run dhclient again you should see the contents of........
What Is Active Directory?
Active Directory is essentially an enhanced, centralized database with a set of objects that make user management, authorization, and data management simpler. Active Directory is synonymous with "Domain Controllers" where a single "domain" often consists of multiple sites and members of the domain. Multiple domains can also be joined to belong to a tree ( a collection of domains). And the highest layer is the forest whi........
You get errors like below and see you have all question marks for the permissions if you go to /run/user/1000/gvfs
If you try to access the mounted share such as anything mounted as gvfs like an SSH share in your file manager you may get an error like this. It generally means an interruption in communication or a fault with gvfsd has caused it.
Solutio........
[root@localhost:~]
BootModuleConfig.sh echo host-ind nfcd........
yes it does create its own json
============================================
cat /tmp/vcsaUiInstaller/ovftool-20180809-175238948-20180809-175603497.log |grep -i json
2018-08-09T17:56:04.238-07:00 verbose OVFTool[30966] [Originator@6876 sub=Default] Manifest file entry: SHA1(VMware-vCenter-Server-Appliance-6.7.0.12000-8832884_OVF10-file1.json) = 1deb658c724767697587d5909c4051c01813e6a1
--> ........
Ithought I'd post this becuase there is some bad information out there. Some guides tell you to edit /etc/postfix/master.cf (-o smtp_bind_address=) but this doesn't work. The same guide also says if you don't change it there you end up changing the listening IP/bind interface which is also not true.
Here is a simple and effective way to change Postfix's sending/binding/outgoing IP address (very important for reverse DNS and so mail servers don't block you)........
#mount the VCSA DVD
mount /dev/sr0 /mnt/cd
#alternatively you could mount the iso directly
mount -o loop vcsa.iso /your/mount/path
#for this purpose we are using the CLI installer on Linux
cd /mnt/cd/vcsa-cli-installer/lin64
#no it's not going to be that easy you can't just run vcsa-deploy like that you need to use a template or configured .json file
./vcsa-deploy
Usage: vcsa-deploy [-h] [--version] [--supported-deploymen........
Centos when copying old files and restarting it seems load everything fine and then says [FAILED] with no log or other message.
service restart named
named [FAILED]
Check more thoroughly you may have missed the error if you have lots of zones!
service named restart|grep error
zone 1.168.192.in-addr.arpa/IN: not loaded due to errors.
zone 2.168.192.in-addr.arpa/IN: no........
Sometimes if you have a very basic configuration OpenVPN on the client side for some reason sends all traffic to the OpenVPN server IP through the tun0 which is of course impossible and creates a block or routing loop.
This is because you need to use your normal ISP/LANgateway to hit the OpenVPN server if it is remote/offsite as is usually the case. So if you are connected to the OpenVPN through say a tun0 device and your routing is set to connect to the OpenVPN&nbs........
You are using Centos 5 which is deprecated so nothing in yum will work until you follow this post to use the vault:
http://realtechtalk.com/Centos_59_Working_Vault_Repo_file-1921-articles
yum update
Loaded plugins: fastestmirror
Loading mirror speeds from cached hostfile
* epel: fedora-archive.ip-connect.vn.ua
Traceback........
Done on Centos 7.3 very important as clearly based on older guides it was a lot easier and more simpler! Hint do not use grub2-install!
If you have trouble booting after this check this CentOS mdadm RAID booting/fixing guide.
One huge caveat if you are an oldschool user or sysadmin who has avoided UEFIbooting
The nor........
In Firefox I cannot connect to any website, proxy is disabled and outside network access is confirmed, no system or manual proxy was set on this Linux Mint/Ubuntu system. Normally this can be caused by proxy or DNS problems and the weird thing is that traceroute and ping to other IPs worked fine but even connecting to sites by IP was not working.
The connection was reset
The connection to the server was reset while the page was loading.........
The Scenario
You have dual NICs and you disable NIC1 which uses 192.168.1.1 as its gateway. With NIC2 you enable it/connect it to another network which also has the gateway 192.168.1.1
Everything will work fine at this point.
When switching back to NIC1 even with NIC2 disabled and even unplugged, the OS basically can't pick up the new/updated ARP entry of the old device for 192.168.1.1 and perhaps thinks it is a security risk or spoof of some sorts and blocks i........
#solution
Edit /etc/yum.repos.d/openvz.repo
For the first two entries comment out #mirrorlist and uncomment #baseurl and then it worked
openvz yum problem Centos 6.5 cannot find file on mirror:
yum update
Loaded plugins: fastestmirror
Determining fastest mirrors
* openvz-kernel-rhel6: mirrors.ustc.edu.cn
* openvz-utils: mirrors.ustc.edu.cn
base ........
#from epel repo
yum -y install opendkim
chkconfig opendkim on
cd /etc/opendkim/keys
opendkim-genkey -vd mail.server.com
opendkim-genkey: generating private key
opendkim-genkey: private key written to default.private
opendkim-genkey: extracting public key
opendkim-genkey: DNS TXT record written to default.txt
........
CPanel says you can access 98% of the functions through CLI which experienced Unix/Linux admins prefer for simplicity and for scripting. I've never found CPanel easy to use from the admin panel, it seems everything is hard to find and a simple task becomes a series of hunts.
So for people like me here's the list: http://cpanel.net/system-administrators/command-line-scrip........
I've only ever seen this in Ubuntu for some reason and it is because of the /etc/nsswitch.conf settings.
So the issue is that if the hostname's reverse DNS cannot be found that you need to go back to DNS which was not the default in this nsswitch.conf file for some strange reason.
Edit /etc/nsswitch.conf and replace your "hosts" line with this:
#hosts: files dns mdns4_minimal [NOTFOUND=return] mdns........
Go to:
"Server Configuration" -> Basic cPanel & WHM Setup
Scroll to: "Nameservers" (at the bottom)
From there you can set the names of the nameserver and their IPs.
It's very weird and confusing that nothing under IP Functions/DNS has or links to this.........
/scripts/phpextensionmgr install PHPSuHosin
Updating md5sum list
Fetching http://httpupdate.cpanel.net/cpanelsync/easy/targz.yaml (connected:0).......(request attempt 1/12)...Resolving httpupdate.cpanel.net...(resolve attempt 1/65)...
Fetching http://httpupdate.cpanel.net/mirror_addr_list (connected:0).......(request attempt 1/3)......connecting to 74.50.120.123...@74.50.120.123......connected......receiving...100%......request success......Done........
pxe-32 tftp open timeout
The solution was to enable tftp in xinetd with "chkconfig tftp on".
See the troubleshooting below:
chkconfig --list
NetworkManager 0:off 1:off 2:off 3:off 4:off 5:off 6:off
acpid 0:off&n........
http://support.godaddy.com/help/article/668/registering-your-own-nameservershosts?pc_split_value=1
Log in to your GoDaddy Account.
Click on "My Account" at the top left.
Click on "Domains".
Click on the "Launch" button for the domain you want to create the nameservers for.
Find........
Add a DNS Zone
Results of adding zone
Sorry, you must enter a domain. Please try again.
Fill this out at the top (Imissed it)
Domain Selection
Ip Domain
The issue was I didn't realize the form above had to be used,I thought it should work where you click on the user, domain and then click on the submit button and you'd go to the next step. But it doesn't, you need to........
No one needs this feature for the most part, so here's what I added to /etc/dhcpd.conf to fix it:
ddns-update-style none;........
This is something I often setup for clients because it's very helpful for people in datacenters, this allows custom OS installs on demand, you can customize it more by using kickstart etc.. but here's a base I use before customizing more:
This little script below will install everything you need to get booting by PXE Linux.
It also assumes you set a local IP (be sure not to overwrite your existing IP) on eth0:0 (note the :0) as 192.168.1.10 and it........
I dread updating the kernel and rebooting to find the Ubuntu graphics aren't working and you have to manually intervene. This is usually because Ubuntu for whatever reason didn't update the drivers you need (eg. the manually compiled Nvidia Kernel driver that MUST be recompiled for each and every kernel update unfortunately).
The most common reason may be that "linux-source" hasn't been installed automatically on my system. I tried to manually reinstall the........
One thing to note about DNS servers and providers is that they aren't always trustworthy, not even if they're Google or your favorite ISP. Any DNS server can compromise your privacy, and they are likely tracking your browsing habits and keeping logs of it. Sometimes it's for Marketing/Research purposes such as Google's GMail service which they admit is scraped/datamined. I would expect nothing less from their DNS service.
The other danger with such widely used and pu........
mod_status is a great way to track down the source of high CPU usage and to find what vhost/script is the cause of it.
It gives you a live view of bandwith usage, CPU usage, and memory usage broken down by domain/vhost and script/URI.
Enable mod_status
vi /etc/httpd/conf/httpd.conf
ExtendedStatus On
SetHandler server-status
Order Deny,Allow
Deny from all
All........
I don't expect this to be solved soon but some of Yahoo's DNS servers are out of whack. I changed the IPs of some nameservers of some domains and now most Yahoo users can't e-mail to those domains!
As you can see below by the "No MX or A records for mychangedomain.com", now Yahoo's DNS/mailserver DNS cache is wrong. You would think they would at least have cached the old incorrect records, but instead for some reason their DNS cache has no entry and doesn't seem........
Centos 5 Postfix and SPAMASSASSIN Tutorial
yum install spamassassin
chkconfig spamassassin on
vi /etc/mail/spamassassin/local.cf
##############
#required_hits 5
#report_safe 0
#rewrite_header Subject [SPAM]
#5 is the least restrictive (means only the most obvious SPAM is caught. 0 is obviously the most restrictive/sensitive and would have lots of false positives
require........
SPAMASSASSIN
Disable OpenWhois RBL (it is dead/defunct/no longer active):
You might see this in your headers
2.4 DNS_FROM_OPENWHOIS RBL: Envelope sender listed in bl.open-whois.org
comment out this inside /usr/share/spamassassin/72_active.cf
##{ DNS_FROM_OPENWHOIS
ifplugin Mail::SpamAssassin::Plugin::DNSEval
header DNS_FROM_OPENWHOIS eva........
Basically you should always be 100% sure that whatever IPyour mail server sends out with has reverse DNS/PTR records. Remember that unless you own your IPs then you won't be able to set your own reverse DNS. Even if you were to create a reverse PTR record on your DNS servers it will be ignored. Reverse DNS is queried to pre-assigned DNS servers of your ISP, so therefore you'll need to contact your ISP/Colo/Hosting provider to do a reverse DNS entry.
If you don't have........
genuine.com/IN: loading master file genuine.com.zone: file not found
_default/genuine.com/IN: file not found
I always found it silly that no one really talks about this and apparently many like me and even control panels like Plesk were still using hard paths. I always thought "why can't I just specify the name of the zone file and have bind find it". Surely the default search path must be /var/named or somewhere else but there is no such thing.........
Webmin/Virtualmin when enabling bind:
Failed to save enabled features : Virtualmin is configured to setup DNS zones, but this system is not setup to use itself as a DNS server. Either add 127.0.0.1 to the list of DNS servers, or turn off the BIND feature on the module config page.
It means what it says, add "127.0.0.1" to /etc/resolv.conf........
The normal solution doesn't help or apply here:
ssh -v user@192.168.5.41
OpenSSH_4.3p2 Debian-9etch3, OpenSSL 0.9.8c 05 Sep 2006
debug1: Reading configuration data /etc/ssh/ssh_config
debug1: Applying options for *
debug1: Connecting to 192.168.5.41 [192.168.5.41] port 22.
debug1: Connection established.
debug1: permanently_set_uid: 0/0
debug1: identity file /root/.ssh/identity type -1
debug1: i........
I've never understood how to enable and disable services for different run levels in Debian based distros, it's just weird, annoying and doesn't make sense. I much prefer chkconfig from RHEL.
Just install the package called 'rcconf' and be done with it. rcconf makes things easy for you.
apt-get install rcconf
Reading package lists... Done
Building dependency tree
Reading state information... Done........
Basically the two main types of distros are Debian and RHEL/Centos based. I'm just going to give a quick overview of how the configuration of IP interfaces works in Debian/Centos based distros.
*Just one thing to remember, when setting IPs statically you have to manually specify a DNS server in /etc/resolv.conf (since DHCP is what normally does it automatically)
Debian/Ubuntu/Kubuntu/MEPIS
The IP (DHCP &........
Basic Port ListingHopefully someone finds this useful or at least interesting.
http://www.sans.org/top20/#u9
Name Port Protocol Description
Small services ........
Icouldn't understand why on one system it took a few minutes to get the SSHlogin prompt when connecting to other systems. The other systems all had the UseDNS parameter set to no, which almost always resolves the login prompt delay.
The reason is Ubuntu and perhaps Debian and other distributions /etc/nsswitch.conf file
Edit yours to have the "hosts" line like so (notice that files and dns are the primary resolution choice........
This is really something the SSHServer developers should consider. The cause of this annoyance is because of failed DNS lookups on your IPaddress, which is especially common for many dedicated/col-located servers and also computers on internal NAT/private networks.
The chances are this is the cause of your SSHSlow/Delayed Login problems.
The easy solution to SSH Login Problems
Edit /etc/ssh/sshd_config
Add this line to disable r........
At this time we can't resolve Enom's website and all DNS requests to their 4 primary name servers are failing, although the hostnames themselves still resolve:
Name Server: DNS1.NAME-SERVICES.COM
Name Server: DNS2.NAME-SERVICES.COM
Name Server: DNS3.NAME-SERVICES.COM
Name Server: DNS4.NAME-SERVICES.COM
Name Server: DNS5.NAME-SERVICES.COM
You would really think Enom, bein........