Don't disable or set SELinux to permissive!

It's a bit offtopic but still worth mentioning it.
I recently stumbled upon a reddit post that, in my opinion, perfectly describes why SELinux should not be disabled or set to permissive in a production enviroment!
By default it is configured quite secure and can prevent further 'damage'. If you need to add or rewrite policies and permissions, the manual is a good source of input. Just my 2 cents.

Feel free to comment and / or suggest a topic.

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Dynamic DNS with BIND and ISC-DHCP

I personally prefer to work with hostnames instead of ip-addresses. If you have anything like freeipa or active directory, it will do that for you by registering the client you added to your realm to the managed dns and edit the records dynamically. We can achieve the same goal with just bind and isc-dhcp. I'll use a raspberry pi with raspbian 9 for this setup. So here is a quick tutorial on how to configure the isc-dhcp-server to dynamically update bind. First set a static ip to your server. [archy@ddns ~]$ sudo vim /etc/network/interfaces # interfaces(5) file used by ifup(8) and ifdown(8) # Please note that this file is written to be used with dhcpcd # For static IP, consult /etc/dhcpcd.conf and 'man dhcpcd.conf' # Include files from /etc/network/interfaces.d: source-directory /etc/network/interfaces.d auto eth0 iface eth0 inet static address 172.31.30.5 network 172.31.30.0 broadcast 172.31.30.255 netmask 255.255.255.0 ...

LACP-Teaming on CentOS 7 / RHEL 7

What is teaming? Teaming or LACP (802.3ad) is a technique used to bond together multiple interfaces to achieve higher combined bandwith. NOTE: every clients speed can only be as high as the single link speed of one of the members. That means, if the interfaces I use in the bond have 1 Gigabit, every client will only have a maximum speed of 1 Gigabit. The advantage of teaming is, that it can handle multiple connections with 1 Gigabit. How many connections depends on the amount of your network cards. I'm using 2 network cards for this team on my server. That means I can handle 2 Gigabit connections at full rate on my server provided the rest of the hardware can deliver that speed. There also exists 'Bonding' in the Linux world. They both do the same in theory but for a detailed comparison check out this article about teaming in RHEL7 . To create a teaming-interface, we will first have to remove all the interface configurations we've done on the (soon to be) sla...

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I recently went over my network configuration and noticed that the dhcp-leases were not pushed into the IPA-DNS yet. So I thought, why not do it now. The setup is very similar to setting it up on a single bind instance not managed by IPA (I've already written a guide about this here ). My setup is done with the following hosts: ipa01.archyslife.lan - 172.31.0.1 inf01.archyslife.lan - 172.31.0.5 First of all, create a rndc-key: [archy@ipa01 ~]$ sudo rndc-confgen -a -b 512 This will create the following file '/etc/rndc-key' [archy@ipa01 ~]$ sudo cat /etc/rndc.key key "rndc-key" { algorithm hmac-md5; secret "secret_key_here=="; }; We also need to make named aware of the rndc-key and allow our remote dhcp server to write dns entries: [archy@ipa01 ~]$ sudo vim /etc/named.conf ... include "/etc/rndc-key"; controls { inet 172.31.0.1 port 953 allow { 172.31.0.5; } keys ...

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Sometimes there's weird errors in IT that occur on random chance. I've had such an encounter with SSSD in combination with IPA(+AD-Trust) recently, where only sometimes, a connection to one of the IPA-Servers would fail with this error: Jul 13 13:36:42 ipa02.archyslife.lan sshd[3478]: pam_sss(sshd:account): Access denied for user runner: 4 (System error) Jul 13 13:36:42 ipa02.archyslife.lan sshd[3478]: fatal: Access denied for user runner by PAM account configuration [preauth] In my case, it was only happening sometimes when running a basic system setup role using ansible on every host in the entire environment. This way, there was no consistent pattern besides being the same host every time if it failed. First up, add the 'debug_level=X' to every section required in the /etc/sssd/sssd.conf where X is a number from 1 to 10 with 10 being the most verbose. Afterward, restart sssd and check the logs for any obvious problems. 1) If you are using local users, check the...

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