Tag Archives: CentOS

Install WordPress on CentOS 7 with SELinux

I’ve been frustrated lately with the number of tutorials for installing WordPress on CentOS 7 that say to simply turn SELinux off. This is an unacceptable workaround. It’s simply lazy administration. SELinux is not designed to make your job harder (although it can do that pretty well), it’s there to make your system safer.

I have scoured the internet and pieced together bits of information from several sources – mainly here, here, and here to put together a tutorial that walks you through how to install WordPress in CentOS7 while keeping SELinux turned on.

It took a lot of reading to understand SELinux, but once you understand it, it makes a whole lot more sense. Go figure.

Apache

Install required packages:

sudo yum -y install httpd
sudo systemctl enable httpd

Modify apache config to allow mod_rewrite:

sudo sed -i /etc/httpd/conf/httpd.conf -e 's/AllowOverride None/AllowOverride All/g'

Open necessary firewall ports:

sudo firewall-cmd --add-service=http --permanent
sudo systemctl restart firewalld

Start apache:

sudo systemctl start httpd

Navigate to your new site to make sure the testing page comes up.

Update 11/4/2016: If you are behind a reverse proxy such as varnish or a web application firewall, you will want to modify your apache configuration to log x-forwarded-for IPs to make the logs more meaningful:

sudo sed -i /etc/httpd/conf/httpd.conf -e 's/%h/%{X-Forwarded-For}i/g'

MariaDB

Install:

sudo yum -y install mariadb-server mariadb
sudo systemctl enable mariadb

Run initial mysql configuration to set database root password

sudo systemctl start mariadb
sudo mysql_secure_installation

Create a wordpress database and user:

mysql -u root -p 
#enter your mysql root password here
create user wordpress;
create database wordpress;
GRANT ALL PRIVILEGES ON wordpress.* To 'wordpress'@'localhost' IDENTIFIED BY 'password';
quit;

WordPress

Install PHP and restart apache

sudo yum -y install php php-mysql php-gd php-ldap php-odbc php-pear php-xml php-xmlrpc php-mbstring php-snmp php-soap curl
sudo systemctl restart httpd

Configure base wordpress directory

Download, extract, and set permissions for your wordpress installation:

wget https://wordpress.org/latest.zip
sudo unzip latest.zip -d /var/www/html
sudo chown apache:apache -R /var/www/html/wordpress

Optional: Change Apache document root so you don’t need to tack /wordpress at the end of the url:

sudo sed -i /etc/httpd/conf/httpd.conf -e 's/DocumentRoot \"\/var\/www\/html/&\/wordpress/g'
sudo systemctl restart httpd

Configure upload directory

If you want users to upload content, then you will want to assign the http_sys_rw_content_t selinux security context for the wp-uploads directory (create it if it doesn’t exist)

sudo mkdir /var/www/html/wordpress/wp-content/uploads
sudo chown apache:apache /var/www/html/wordpress/wp-content/uploads
sudo semanage fcontext -a -t httpd_sys_rw_content_t "/var/www/html/wordpress/wp-content/uploads(/.*)?"
sudo restorecon -Rv /var/www/html/wordpress/wp-content/uploads

Run the wizard

In order for the wizard to run properly we need to temporarily give the wordpress directory httpd_sys_rw_content_t selinux context

sudo chcon -t httpd_sys_rw_content_t /var/www/html/wordpress/

Now navigate to your new website in a browser and follow the wizard, which will create a wp-config.php file inside the wordpress directory. Once your site is properly set up, restore the original security context for the wordpress directory:

sudo restorecon -v /var/www/html/wordpress/

Success! Everything is working within the proper SELinux contexts.

Troubleshooting

Permission denied when accessing /wordpress

The obvious thing to check is to make sure the directory /var/www/html/wordpress has the ownership set to apache. That didn’t fix my issue, though. Thanks to serverfault I narrowed this down to a selinux permissions issue.  Changing the selinux context to httpd_sys_content_t for the wordpress folder fixed the issue.

sudo semanage fcontext -a -t httpd_sys_content_t /var/www/html/wordpress/
sudo restorecon -v /var/www/html/wordpress/

Sorry, but I can’t write the wp-config.php file.

“You can create the wp-config.php manually and paste the following text into it.”

I had a suspicion that writing files was also a selinux issue. This was confirmed when I decided to tail /var/log/audit/audit.log and found this when the wordpress installer tried to write wp-config.php:

type=AVC msg=audit(1475596102.558:16868): avc: denied { write } for pid=5751 comm="httpd" name="wordpress" dev="dm-0" ino=68494934 scontext=system_u:system_r:httpd_t:s0 tcontext=system_u:object_r:httpd_sys_content_t:s0 tclass=dir
type=SYSCALL msg=audit(1475596102.558:16868): arch=c000003e syscall=21 success=no exit=-13 a0=7f9f4b931478 a1=2 a2=0 a3=1 items=0 ppid=5740 pid=5751 auid=4294967295 uid=48 gid=48 euid=48 suid=48 fsuid=48 egid=48 sgid=48 fsgid=48 tty=(none) ses=4294967295 comm="httpd" exe="/usr/sbin/httpd" subj=system_u:system_r:httpd_t:s0 key=(null)

This led me to find this great explanation from Francis Pereira on how to get wordpress and selinux to peacefully coexist. Also thanks to the excellent Redhat Manual for more information on what to do, combined with this very helpful guide from serverlab.

First, we need to temporarily grant httpd_sys_rw_content_t to the wordpress directory. This is to allow the initial wizard to create the wp-config.php file.

sudo chcon -t httpd_sys_rw_content_t /var/www/html/wordpress/

Now you can run the wizard and it will work properly.

Once your site is set up, restore the context to http_sys_content_t

sudo restorecon -v /var/www/html/wordpress/

Resizing LVM storage checklist

This is a short note of what to do when you change size of the physical disk an LVM setup, such as the default configuration in CentOS 7.

  1. Modify the physical disk size
  2. Modify the partition size
    1. I used fdisk to delete the partition, then re-create with a larger size
    2. Reboot
  3. Extend the physical volume size
    1. pvresize <path to enlarged partition>
  4. Extend the logical volume size
    1. lvextend <lv path> -l100%FREE
  5. Extend filesystem size
    1. resize2fs <lv path>
    2. #If you're running CentOS 7, the default filesystem is actually XFS, not ext4. In that case:
      xfs_growfs <lv path>
  6. Profit.

Compile ffmpeg on CentOS 7

Recently I had to compile ffmpeg from scratch on CentOS 7. The reason? I wanted libfdk_aac support. Here are my notes on the procedure. The how-to on https://trac.ffmpeg.org/wiki/CompilationGuide/Centos was actually quite helpful and accurate.

Install necessary dependencies and set up build folder

yum install autoconf automake cmake freetype-devel gcc gcc-c++ git libtool make mercurial nasm pkgconfig zlib-devel
mkdir ~/ffmpeg_sources

Build necessary components
I only needed x264 and libfdk_aac, so that’s all I ended up doing:

#yasm
cd ~/ffmpeg_sources
git clone --depth 1 git://github.com/yasm/yasm.git
cd yasm
autoreconf -fiv
./configure --prefix="$HOME/ffmpeg_build" --bindir="$HOME/bin"
make
make install
make distclean
#libx264
cd ~/ffmpeg_sources
git clone --depth 1 git://git.videolan.org/x264
cd x264
PKG_CONFIG_PATH="$HOME/ffmpeg_build/lib/pkgconfig" ./configure --prefix="$HOME/ffmpeg_build" --bindir="$HOME/bin" --enable-static
make
make install
make distclean
#libfdk_aac
cd ~/ffmpeg_sources
git clone --depth 1 git://git.code.sf.net/p/opencore-amr/fdk-aac
cd fdk-aac
autoreconf -fiv
./configure --prefix="$HOME/ffmpeg_build" --disable-shared
make
make install
make distclean

Compile ffmpeg
I actually specified a git mirror because the sources at ffmpeg site were glacially slow.

cd ~/ffmpeg_sources
git clone https://github.com/FFmpeg/FFmpeg.git
cd FFmpeg
PKG_CONFIG_PATH="$HOME/FFmpeg_build/lib/pkgconfig" ./configure --prefix="$HOME/FFmpeg_build" --extra-cflags="-I$HOME/FFmpeg_build/include" --extra-ldflags="-L$HOME/FFmpeg_build/lib" --bindir="$HOME/bin" --pkg-config-flags="--static" --enable-gpl --enable-nonfree --enable-libfdk-aac  --enable-libx264
make
make install
make distclean
hash -r

Optionally, remove existing ffmpeg

sudo yum remove ffmpeg

That was it! After a bit of compile time ffmpeg worked with the items I wanted it to.

Linux two factor user exception

Two factor authentication is much more security than simply password authentication. There are times, though, that you will want to create an exception for a specific user. In my case, I wanted to allow a vulnerability scanner to scan my systems. Rather than turn  two factor off for the duration of the scan, I set out to learn how to add an exception for a specific user. I accomplished this on CentOS 6 Linux, but it works an any Linux version using PAM.

The solution to my problem is the pam_listfile PAM module. Pam_listfile allows you to specify a text file that contains a list of either users or groups. You then tell PAM what to do with the file (allow, deny) as well as how to handle what to do if it can’t read the file for some reason.

Thanks to this site I learned the details of what to do. In my case I want a single username to not be prompted for a 2nd authentication factor. All other users must use two factors. I created the file /etc/scan_user and added the username I wanted to have the exception:

echo "scanuser" > /etc/scanuser

Then I modified /etc/pam.d/password-auth and placed it after the first authentication factor, but before the second.

vi /etc/pam.d/password-auth
#First authentication factor
auth        required    pam_unix.so

#pam_listfile to check username and see if it's allowed with only one factor or must provide a second
auth        sufficient  pam_listfile.so onerr=fail item=user sense=allow file=/etc/qualys_user

#Second authentication factor. This is only reached if the user is not on the list provided in pam_listfile.
auth        required   pam_google_authenticator.so

The PAM configuration is as follows:

  • First factor required for everyone (pam_unix)
  • pam_listfile sufficient for anyone who matches the provided list.
  • Second factor required for everyone else (anyone who wasn’t on the pam_listfile list

My vulnerability scanner is now happy and I still have two factor authentication enabled for every other user in the system. Success.

 

Configure HDHR Viewer XMLTV in CentOS Linux

Recently I’ve accomplished the herculean task of setting up my parents’ cable connection to stream through Plex using a HD Homerun 3 cablecard network tuner. It works! This is how I got XMLTV guide working for the HDHR Viewer plugin for Plex on CentOS 7 Linux.

Required reading: http://hdhrviewer.zynine.net/hdhrviewerv2-initial-setup/xmltv-zap2xml/

First, install and configure the required perl and java packages

sudo yum install perl-Compress-Zlib perl-HTML-Parser perl-HTTP-Cookies perl-LWP-Protocol-https perl-JSON gcc cpan java-1.7.0-openjdk-headless 
sudo cpan JSON::XS 
#accept all defaults when prompted

Download the zap2xml perl module (zap2xml.pl) Place it somewhere it can be easily accessed.

Test to make sure the script will run properly:

perl zap2xml.pl -u <zap2it username> -p <zap2it password>

If you get an error like this:

Can't locate Compress/Zlib.pm in @INC (@INC contains: /usr/local/lib64/perl5 /usr/local/share/perl5 /usr/lib64/perl5/vendor_perl /usr/share/perl5/vendor_perl /usr/lib64/perl5 /usr/share/perl5 .) at zap2xml.pl line 26.

It means you haven’t installed the correct perl modules. Double check that you installed them all.

Once we know it runs properly e need to configure a cron job to run zap2xml daily (to make sure the guide data is always up to date.)

crontab -e
#press i to begin inserting
0 0 * * * perl <full path to where you downloaded zap2xml>/zap2xml.pl -u <zap2it e-mail> -p <zap2it password>
#ESC :wq to save and exit

 

Next download and unzip the Channel Guide app. I placed it in the same place I downloaded zap2xml to keep things simple.

Test it out to make sure it works:

java -jar channel-guide-app-0.0.3.jar server app-config.yml

If it starts and doesn’t crash, you know it’s working.

Now we want to configure the channel guide app to run on startup

sudo vi /etc/systemd/system/channelguide.service
[Unit]
Description=Plex Channel Guide

[Service]
TimeoutStartSec=0
ExecStart=/usr/bin/java -jar <full path to channel-guide dir>/channel-guide-app-0.0.3.jar server <full path to channel-guide dir>/app-config.yml

[Install]
WantedBy=multi-user.target

Make sure this systemd service is enabled:

sudo systemctl enable /etc/systemd/system/channelguide.service

Lastly make sure you’ve configured the HDHRViewer plugin in Plex to use xmltv and rest API as per the how-to on their site.

Success!

Change the hostname on a Splunk Indexer

Recently I set about to change the hostname on a Splunk indexer. It should be pretty easy, right? Beware. It can be pretty nasty! Below is my experience.

I started with the basics.

  • hostname command
    hostname <newhostname>
  • Modify /etc/system/network to make it persistent (CentOS specific)
    sed -i 's/<old hostname>/<new hostname>/g' /etc/system/network
  • Inform Splunk of the hostname change
    sed -i 's/<old hostname>/<new hostname>/g' $SPLUNK_HOME/etc/system/local/server.conf
  • Restart Splunk

Sadly, that wasn’t the end of it. I noticed right away Splunk complained of a few things:

TcpOutputProc - Forwarding to indexer group default-autolb-group blocked for 300 seconds.
WARN TcpOutputFd - Connect to 10.0.0.10:9997 failed. Connection refused

Running

netstat -an | grep LISTEN

revealed that the server was not even listening on 9997 like it should be. I found this answer indicating it could be an issue with DNS tripping up on that server. I edited $SPLUNK_HOME/etc/system/local/inputs.conf with the following:

[splunktcp://9997]
connection_host = none

but I also noticed that after I ran the command a short time later it was no longer listening on 9997. Attempting to telnet from the forwarder to the indexer in question revealed the same results – works at first, then quit working. Meanwhile no events are getting stored on that indexer.

I was pulling my hair out trying to figure out what was happening. Finally I discovered this gem on Splunk Answers:

Are you using the deployment server in your environment? Is it possible your forwarders’ outputs.conf got deployed to your indexer?

On the indexer:
./splunk cmd btool outputs list –debug

Sure enough! after running

./splunk cmd btool outputs list --debug

I discovered this little gem of a stanza:

/opt/splunk/etc/apps/APP_Forwarders/default/outputs.conf [tcpout]

That shouldn’t’ have been there! Digging into my deployment server I discovered that I had a server class with a blacklist, that is, it included all deployment clients except some that I had listed. The blacklist had the old hostname, which meant when I changed the indexer’s hostname it no longer matched the blacklist and thus was deployed a forwarder’s configuration, causing a forwarding loop. My indexer was forwarding back to the forwarder everything it was getting from the forwarder, causing Splunk to shut down port 9997 on the offending indexer completely.

After getting all that set up I noticed Splunk was only returning searches from the indexers whose hostnames I had not changed. Everything looked good in the distributed search arena – status was OK on all indexers; yet I still was not getting any results from the indexer whose name I had changed, even though it was receiving events! This was turning into a problem. It was creating a blind spot.

Connections great, search status great, deployment status good.. I didn’t know what else to do. I finally thought to reload Splunk on the search head that had been talking to the server whose name I changed. Success! Something in the search head must have made it blind to the indexer once its name had changed. Simply restarting Splunk on the search head fixed it.

In short, if you’re crazy enough to change the name of one of your indexers in a distributed Splunk environment, make sure you do the following:

  • Change hostname on the OS
  • Change ServerName in Splunk config files
    • Add connection_host = none in inputs.conf (optional?)
  • Clean up your deployment server
    • Delete old hostname from clients phoning home
    • MAKE SURE the new hostname won’t be sucked up into an unwanted server class
  • Clean up your search head
    • Delete old hostname search peer
    • Add new hostname search peer
    • Restart search head
  • Profit

Install Owncloud 8 on Centos 7

I recently needed to re-install my Owncloud VM. I’ve been on a CentOS kick lately so I decided to see if I could install OwnCloud 8 on a Centos 7 base install. It turned out to not be as easy as I thought it would be.

When I tried to install owncloud on my CentOS 7 system, I kept getting a 404 error message even though I followed the documentation outlined here.

It turns out that they changed where the RPM is held and apparently forgot to update the documentation. I discovered this by manually navigating to download.suse.org/repositories/isv:ownCloud:community and browsing the directories. The documentation has you grab a repo from Centos_Centos-7 folder, which is broken. It looks like the proper directory is just Centos_7.

I had to remove the old repo, purge the cache, and try again. To do so, remove the .repo file and purge via yum:

cd /etc/yum.repos/d/
rm isv\:ownCloud\:community.repo
yum --enablerepo=isv_ownCloud_community clean metadata
wget http://download.opensuse.org/repositories/isv:ownCloud:community/CentOS_7/isv:ownCloud:community.repo
yum install owncloud

The above procedure is what you should run if you’ve already tried to use the broken link in the documentation and failed. If you haven’t installed owncloud yet, do the following

cd /etc/yum.repos/d/
wget http://download.opensuse.org/repositories/isv:ownCloud:community/CentOS_7/isv:ownCloud:community.repo
yum install owncloud

Success.

Install Splunk Universal Forwarder on Linux

I do this infrequently enough that I decided I should really write this down. Below is the quick and dirty way to get the Splunk universal forwarder installed on a new Linux  system. Thanks to byteschef for the information used to create this guide.

Download the latest splunk .RPM from their site and install it via RPM -i <filename> (if RedHat based) or dpki -i <filename> if debian based.

Run the following commands as root:

cd /opt/splunkforwarder/bin
./splunk start --accept-license
./splunk enable boot-start
./splunk add forward-server <IP/hostname of splunk server>:9997 -auth admin:changeme
./splunk add monitor /var/log
./splunk edit user admin -password NEW_PASSWORD -auth admin:changeme
./splunk restart

If there are any other directories you want monitored other than /var/log (application logs, for example) then issue:

./splunk add monitor <directory to monitor>

Done.

Troubleshoot RSA SecurID in CentOS 6

Unexpected error from ACE/Agent API.

In following this guide for configuring a CentOS 6 system to authenticate with RSA SecurID I came across an unusual error message that had me scratching my head:

Unexpected error from ACE/Agent API.

The problem stemmed from having an incorrect value in the /var/ace/sdopts.rec file for CLIENT_IP. For some reason I had put the IP address of the RSA authentication server in there. CLIENT_IP is the IP address of the RSA client, or rather, the machine you’re working on. The client uses whatever’s in that file to report to the RSA server what its IP address is. If the RSA server gets an invalid IP response from the client, it won’t authenticate.

SELinux issues

Much blood and tears were shed in dealing with getting SELinux to exist harmoniously with RSA SecurID. The problem was exacerbated my the fact that there is a lot of half solutions and misinformation floating out there on the internet. This will hopefully help fix that.

The message entry does not exist for Message ID: 1001

At this point acetest worked beautifully but I could not use an RSA passcode to SSH into the system. Digging into the log revealed this error message:

sshd[2135]: ACEAGENT: The message entry does not exist for Message ID: 1001

Thanks to this post, I realized it was due to selinux. Modifying the selinux config information to allow /var/ace to be read, per the commands below, seemed to fix the issue.

setenforce 0
chcon -Rv --type=sshd_t /var/ace/
setenforce 1

But alas! The solution was not a very good one. The commands above have two problems with them: first, the chcon command is temporary and does not survive selinux policy relabels; second, it assigns the type sshd_t, which does allow SSH to access it, but revokes RSA SecurID’s ability to write to the directory. This is a problem if you ever need to clear node secrets. The server will initiate the wipe but the client will not be able to modify that directory, resulting in node secret mismatches.

I finally decided to RTFM and landed on this documentation page, which explained the issue I was having: selinux mislabeling. The proper solution to this problem is use a label that both SecurID and SSHD can write / read to. Thanks to this SELinux Manpage (it really pays to RTFM!) I discovered that the label I want is var_auth_t (the default label applied when creating /var/ace is var_t, which SSH can’t read.) 

To survive relabeling, use the semanage command, which is not installed by default. Thanks to this site I learned I must install policycoreutils-pithon:

yum install policycoreutils-python

Once semanage is installed, use it to change the label for /var/ace and everything inside it to var_auth_t, then apply the changes with restorecon:

semanage fcontext -a -t var_auth_t "/var/ace(/.*)?"
restorecon -R -v /var/ace

Finally, both RSA SecurID and OpenSSH can read what they need to and authentication is successful.

First acetest succeeds but subsequent ones fail

If you followed the bad advice of relabeling /var/ace to sshd_t you might run across a very frustrating issue where acetest would succeed, but any attempts to SSH into the box or even run acetest again would fail. The error message on the RSA SecurID server was

Node secret mismatch: cleared on server but not on agent

The problem is due to the improper SELinux labeling mentioned above. The fix is the same:

yum install policycoreutils-python
semanage fcontext -a -t var_auth_t "/var/ace(/.*)?"
restorecon -R -v /var/ace

SSH access denied even with successful acetest

If acetest succeeds and you’ve loaded the module into PAM but still get access denied, it could be due to your SSH configuration. Ensure the following options are set:

ChallengeResponseAuthentication yes 
UsePrivilegeSeparation no

Victory.

Join a CentOS machine to an AD domain

I ran into enough snags when attempting to join an CentOS 6.6 machine to a Microsoft domain that I thought I would document them here. Hopefully it is of use to someone. The majority of the experience is thanks to this site.

Update 03/16/2015: I came across this site which makes things a little easier when it comes to initial configuration – messing with other config files is no longer necessary. The authconfig command to do this is below:

authconfig --disablecache --enablelocauthorize --enablewinbind --enablewinbindusedefaultdomain --enablewinbindauth        --smbsecurity=ads --enablekrb5 --enablekrb5kdcdns --enablekrb5realmdns --enablemkhomedir --enablepamaccess --updateall        --smbidmapuid=100000-1000000 --smbidmapgid=100000-1000000 --disablewinbindoffline --winbindjoin=Admin_account --winbindtemplateshell=/bin/bash --smbworkgroup=DOMAIN --smbrealm=FQDN --krb5realm=FQDN

Replace DOMAIN with short domain name, FQDN with your fully qualified domain name, and Admin_account with an account with domain admin privileges, then skip to the Reboot section, as it covers everything before that.

Install the necessary packages

yum -y install authconfig krb5-workstation pam_krb5 samba-common oddjob-mkhomedir

Configure kerberos auth with authconfig

There is a curses-based GUI you can use to do this in but I opted for the command line.

authconfig --disablecache --enablewinbind --enablewinbindauth --smbsecurity=ads --smbworkgroup=DOMAIN --smbrealm=DOMAIN.COM.AU --enablewinbindusedefaultdomain --winbindtemplatehomedir=/home/DOMAIN/%U --winbindtemplateshell=/bin/bash --enablekrb5 --krb5realm=DOMAIN.COM.AU --enablekrb5kdcdns --enablekrb5realmdns --enablelocauthorize --enablemkhomedir --enablepamaccess --updateall

Add your domain to kerberos configuration

Kerberos information is stored in /etc/krb5.conf. Append your domain in the realms configuration, like below

vi /etc/krb5.conf
[realms]
 EXAMPLE.COM = {
 kdc = kerberos.example.com
 admin_server = kerberos.example.com
 }
 
DOMAIN.COM.AU = {
admin_server = DOMAIN.COM.AU
kdc = DC1.DOMAIN.COM.AU
kdc = DC2.DOMAIN.COM.AU
}
 
[domain_realm]
 .example.com = EXAMPLE.COM
 example.com = EXAMPLE.COM
 domain.com.au = DOMAIN.COM.AU
 .domain.com.au = DOMAIN.COM.AU

 Test your configuration

Use the kinit command with a valid AD user to ensure a good connection with the domain controllers:

kinit <AD user account>
It should return you to the prompt with no error messages. You can further make sure it worked by issuing the klist command to show open Kerberos tickets
klist

Ticket cache: FILE:/tmp/krb5cc_0
Default principal: someaduser@DOMAIN.COM.AU
Valid starting Expires Service principal
02/27/14 12:23:21 02/27/14 22:23:21 krbtgt/DOMAIN.COM.AU@DOMAIN.COM.AU
renew until 03/06/14 12:23:19
When I tried the kinit command it returned an error:
kinit: KDC reply did not match expectations while getting initial credentials
 After scratching my head for a while I came across this site, which explains that your krb5.conf is case sensitive – it must all be all upper case. Fixing my krb5.conf to be all caps for my domain resolved that issue.

Join the domain

net ads join domain.com.au -U someadadmin
When I tried to join the domain I received this lovely message:
Our netbios name can be at most 15 chars long, "EXAMPLEMACHINE01" is 16 chars long
Invalid configuration. Exiting....
Failed to join domain: The format of the specified computer name is invalid.
Thanks to Ubuntu forms I learned I needed to edit my samba configuration to assign an abbreviated NETBIOS name to my machine.
vi /etc/samba/smb.conf
Uncomment the “netbios name =” line and fill it in with a shorter (max 15 characters) NETBIOS name.
netbios name = EXAMPLE01
You can test to ensure the join was successful with this command
net ads testjoin

Configure home directories

The authconfig command above included a switch for home directories. Make sure you create a matching directory and set appropriate permissions for it.

mkdir /home/DOMAIN
setfacl -m group:"Domain Users":rwx /home/DOMAIN #the article calls to do this, this command doesn't work for me but home directories still appear to be created properly

Reboot

To really test everything the best way is to reboot the machine. When it comes back up, log in with Active Directory credentials. It should work!

Account lockout issues

I ran into a very frustrating problem where everything works dandy if you get the password correct on the first try, but if you mess up even once it results in your Active Directory account being locked. You were locked out after the first try. Each login, even when successful, had this in the logs:

winbind pam_unix(sshd:auth): authentication failure

This problem took a few days to solve. Ultimately it involved modifying two files:

vi /etc/pam.d/system-auth
vi /etc/pam.d/password-auth

As far as I can tell, the problem was a combination of pam_unix being first (which always failed when using AD login), as well as having both winbind and kerberos enabled. The fix was to change the order of each mention of pam_unix to be below any mention of pam_winbind. The other fix I had to do was to comment out mentions of pam_krb5 completely.

#auth        sufficient    pam_krb5.so use_first_pass

Restrict logins

The current configuration allows any domain account to log into the machine. You will probably want to restrict who can log in to the machine to certain security groups. The problem: many Active Directory security groups contain spaces in their name, which Linux doesn’t like.

How do you add a security group that contains a space? Escape characters don’t seem to work in the pam config files.  I found out thanks to this site that it is easier to just not use spaces at all. Get the SID of the group instead.

Use wbcinfo -n to query the group in question, using the backslash to escape the space. It will return the SID we desire.

wbinfo -n Domain\ Users
S-1-5-21-464601995-1902203606-794563710-513 Domain Group (2)

Next, modify /etc/pam.d/password-auth and add the require_membership_of argument to pam_winbind.so:

auth        sufficient    pam_winbind.so require_membership_of=S-1-5-21-464601995-1902203606-794563710-513

That’s it! Logins are now restricted to the security group listed.

Configure sudo access

Sudo uses a different list for authorization, which amusingly, handles escaped spaces just fine.  Simply add the active directory group in sudo as you a local one, eg using a % and then group name, escaping spaces with a backslash:

%Domain\ Users ALL=(ALL) ALL

Rejoice

You’ve just gone through a long and painful battle. Hopefully this article helped you to achieve victory.