Tag Archives: CentOS 7

Add multiple search domains in CentOS 7

I needed to add multiple domains to search DNS with on my Cent7 box. It turns out there are two ways to do it. Cent7 uses networkmanager, so you can use the cli tool to add what you want, or you can edit the file directly.

Using nmcli:

sudo nmcli con mod eth0 ipv4.dns-search "domain1.org,domain2.org,domain3.org"

This causes nmcli to add this line to your network interface config file (/etc/sysconfig/network-scripts/ifcfg-eth0 in my case)

DOMAIN="domain1.org domain2.org domain3.org"

After either using nmcli or manually editing your file, simply restart the network service and your search domains now work!

Add static route in CentOS7

I recently began a project of segmenting my LAN into various VLANs. One issue that cropped up had me banging my head against the wall for days. I had a particular VM that would use OpenVPN to a private VPN provider. I had that same system sending things to a file share via transmission-daemon.

Pre-subnet move everything worked, but once I moved my file server to a different subnet suddenly this VM could not access it while on the VPN. Transmission would hang for some time before finally saying

transmission-daemon.service: Failed with result 'timeout'.

The problem was since my file server was on a different subnet, it was trying to route traffic to it via the default gateway, which in this case was the VPN provider. I had to add a specific route to tell the server to use my LAN network instead of the VPN network in order to restore connectivity to the file server (thanks to this site for the primer.)

I had to create a file /etc/sysconfig/network-scripts/route-eth0 and give it the following line: via dev eth0

This instructed my VM to get to the 192.168.2 network via the gateway on eth0. Restart the network service (or reboot) and success!

Create local CentOS 7 Repo

I’ve recently needed to create a local mirror of Cent7 packages. I followed the guide posted on techmint but also made a few tweaks to get it to work to my liking.

Create local repo mirror

  • Install necessary packages
    • sudo yum -y install epel-release nginx createrepo yum-utils moreutils
  • Create directories that will host your repo
    • sudo mkdir -p /usr/share/nginx/html/repos/{base,centosplus,extras,updates,epel}
  • Use the reposync tool to synchronize to those local directories (repeat for each directory, changing repoid= value to match)
    • reposync -g -l -d -m --repoid=base --newest-only --download-metadata --download_path=/usr/share/nginx/html/repos/
  • Use the createrepo tool to create repodata
    • base & epel have a group file, other repos do not.
    • For base & epel:
      • createrepo -g comps.xml /usr/share/nginx/html/repos/<FOLDER>
    • For the rest:
      • createrepo /usr/share/nginx/html/repos/<FOLDER>

Configure daily synchronization via cron

Copy this script to /etc/cron.daily/ and give it execute rights

##specify all local repositories in a single variable
LOCAL_REPOS="base extras updates epel centosplus"
##a loop to update repos one at a time
for REPO in ${LOCAL_REPOS}; do
reposync -g -l -d -m --repoid=$REPO --newest-only --download-metadata --download_path=/usr/share/nginx/html/repos/Cent7/
if [[ $REPO = 'base' || $REPO = 'epel' ]]; then
        createrepo -g comps.xml /usr/share/nginx/html/repos/Cent7/$REPO/
        createrepo /usr/share/nginx/html/repos/Cent7/$REPO/
chmod 755 /etc/cron.daily/<script_name>

E-mails from cron became annoying. I wanted to only get e-mailed on error. The solution is to use chronic

Modify /etc/anacrontab to add “chronic” between nice and run-parts

1 5 cron.daily nice chronic run-parts /etc/cron.daily
7 25 cron.weekly nice chronic run-parts /etc/cron.weekly
@monthly 45 cron.monthly nice chronic run-parts /etc/cron.monthly


Update 4/25/19 I encountered an issue while trying to use repsync to mirror the remi repo.

warning: /usr/share/nginx/html/repos/Cent7/remi/remi/aspell-nl-0.50-1.el7.remi.x86_64.rpm: Header V4 DSA/SHA1 Signature, key ID 00f97f56: NOKEY

I found out from here that it means you need to manually import the package’s key into the RPMDB like so

sudo rpm --import /etc/pki/rpm-gpg/RPM-GPG-KEY-remi

Recover files from ZFS snapshot of ProxMox VM

I recently needed to restore a specific file from one of my ProxMox VMs that had been deleted. I didn’t want to roll back the entire VM from a previous snapshot – I just wanted a single file from the snapshot. My snapshots are handled via ZFS using FreeNAS.

Since my VM was CentOS 7 it uses XFS, which made things a bit more difficult. I couldn’t find a way to crash-mount a read-only XFS snapshot – it simply resufed to mount, so I had to make everything read/write. Below is the process I used to recover my file:

On the FreeNAS server, find the snapshot you wish to clone:

sudo zfs list -t snapshot -o name -s creation -r DATASET_NAME

Next, clone the snapshot


Next, on a Linux box, use SSHFS to mount the snapshot:

mkdir Snapshot
sshfs -o allow_other user@freenas:/mnt/CLONED_SNAPSHOT_NAME Snapshot/

Now create a read/write loopback device following instructions found here:

sudo -i #easy lazy way to get past permissions issues
cd /path/to/Snapshot/folder/created/above
losetup -P -f VM_DISK_FILENAME.raw
#Take note of output, it's likely set to /dev/loop0 unless you have other loopbacks

Note if your VM files are not in RAW format, extra steps will need to be taken in order to convert it to RAW format.

Now we have an SSH-mounted loopback device ready for mounting. Things are complicated if your VM uses LVM, which mine does (CentOS 7). Once the loopback device is set, lvscan should see the image’s logical volumes. Make the desired volume active

sudo lvscan
sudo lvchange -ay /dev/VG_NAME/LV_NAME

Now you can mount your volume:

mkdir Restore
mount /dev/VG_NAME/LV_NAME Restore/

Note: for XFS you must have read/write capability on the loopback device for this to work.

When you’re done, do your steps in reverse to unmount the snaspshot:

#Unmount snapshot
umount Restore
#Deactivate LVM
lvchange -an /dev/VG_NAME/LV_NAME
Remove loopback device
losetup -d /dev/loop0 #or whatever the loopback device was
#Unmount SSHfs mount to ZFS server
umount Snapshot

Finally, on the ZFS server, delete the snapshot:

sudo zfs destroy CLONED_SNAPSHOT_NAME


When I tried to mount the LVM partition at this point I got this error message:

mount: /dev/mapper/centos_plexlocal-root: can't read superblock

It ended up being because I was accidentally creating a read-only loopback device. I destroy the loopback device and re-created with write support and all was well.

Upgrading AWX

AWX is the open source version of Ansible Tower. It’s a powerful tool, but unfortunately AWX has no in place upgrade capability. If you want to upgrade your AWX to the latest version it takes a bit of trickery (the easy way out being just to pay for Ansible Tower.)

Essentially to upgrade AWX you need to spin up a completely new instance and then migrate your data over to it. Fortunately there is a script out there that makes doing this a bit easier.

Below are my notes for how I upgraded my instance of AWX from version 1.0.6 to 2.1.0.

Create temporary AWX migration server

Spin up new server with ansible installed, then clone AWX

git clone https://github.com/ansible/awx.git 
cd awx 
git clone https://github.com/ansible/awx-logos.git

Modify AWX install to expose 5432 externally:

edit installer/roles/local_docker/tasks/standalone.yml and add

      - "5432:5432" 

right above the when: pg_hostname is not defined or pg_hostname == '' line. Complete stanza looks like this:

- name: Activate postgres container
    name: postgres
    state: started
    restart_policy: unless-stopped
    image: "{{ postgresql_image }}"
      - "{{ postgres_data_dir }}:/var/lib/postgresql/data:Z"
      POSTGRES_USER: "{{ pg_username }}"
      POSTGRES_PASSWORD: "{{ pg_password }}"
      POSTGRES_DB: "{{ pg_database }}"
      PGDATA: "/var/lib/postgresql/data/pgdata"
      - "5432:5432"
  when: pg_hostname is not defined or pg_hostname == ''
  register: postgres_container_activate

Make sure you have port 5432 open on your host-based firewall.

Install AWX on the new host. Verify you can log into the empty instance and that it’s the version you want to upgrade to.

Prepare original AWX server to send

Kill the AWX postgres container on the source machine, and re-run awx installer after modifying it to expose its postgres port as described above.

Install tower-cli (this can be on either source or destination servers)

sudo pip install ansible-tower-cli

Configure tower-cli

tower-cli config username SRC_AWX_USERNAME
towercli config password SRC_AWX_PASSWORD
towercli config host SRC_AWX_HOST

Make sure to use full ansible URL as accessed from a browser for both source and destination

Install awx-migrate:

git clone https://github.com/autops/awx-migrate.git

Update awx-migrate/awx-migrate-wrapper with correct source and destination info

Run awx-migrate-wrapper. It will generate json files with your configuration.

Migrate database to temporary server

Modify tower-cli config, set host, username and password to that of the destination AWX instance

tower-cli config username DEST_AWX_USERNAME
towercli config password DEST_AWX_PASSWORD
towercli config host: DEST_AWX_HOST

Send JSON info to destination:

tower-cli send awx-data.json

You will now have a fresh new, updated AWX instance working, with imported database, on the destination host. Confirm you can log into it with the admin account you set it up with.

Prepare original AWX server to receive

Now, on the source, remove  the old AWX docker containers:

sudo docker rm -f postgres awx_task awx_web memcached rabbitmq

Move / delete the database folder the postgres docker container was using (as defined in awx installer inventory) in my case:


Remove and re-install AWX folder with a fresh git checkout

rm -rf awx
git clone https://github.com/ansible/awx.git
cd awx
git clone https://github.com/ansible/awx-logos.git

Re-run the AWX installer to re-create a blank database on the source host, modify the new awx/installer/inventory as needed. Also modify installer/roles/local_docker/tasks/standalone.yml as outlined above.

cd awx/installer
sudo ansible-playbook -i inventory install.yml

Migrate from temporary AWX server back to source AWX server

Once a new, empty version of awx is running on the source host,  start the awx-migrate process in reverse to migrate the database on the destination instance back to the source. Modify awx-migrate-wrapper and tower-cli to switch src and destination (the destination has become the source and the source has become the destination)

Use awx-migrate-wrapper to generate  new ansible version json files (don’t confuse them with the old json files – best to delete / move all json files before running awx-migrate-wrapper)

Modify tower-cli to point to original AWX URL

Run tower-cli send awx-data.json

Once completed, log in as the admin account. Input LDAP BIND password under settings, then delete any imported LDAP users.


You may want to remove the exposed postgres database ports. Simply undo the changes you made in awx/installer/roles/local_docker/tasks/standalone.yml to remove the Ports part of the first play, then remove your postgres container and re-install AWX with install.yml

Also remember to delete the JSON files generated with awx-migrate as they contain all your credentials in plaintext.



Active Directory / LDAP integration with WordPress

I struggled for a while to get WordPress to use Active Directory credentials on CentOS 7. Below is how I finally got it to work.

First, install necessary packages:

sudo yum -y install openldap-clients php-ldap

If you use self-signed certificate for ldaps, you’ll need to modify /etc/openldap/ldap.conf

PORT 636

With the above settings you can test your ldap string with ldapsearch

ldapsearch -x -D "<BIND USERNAME>" -b "<BASE_DN>" -H ldaps://<LDAP_SERVER_HOSTNAME> -W sAMAccountName=<USER_TO_QUERY>

Once ldapsearch works properly, install your AD integration plugin.  I use AuthLDAP by Andreas Heigl

I struggled with which LDAP strings and filters to use. This is what finally got everything working with our Active Directory environment:




User-ID Attribute: sAMAccountName

Second Name Attributesn


Group-Separator:  _

Group-Filter: (&(objectClass=user)(sAMAccountName=%s)(memberOf=*))

Role – group mapping

I had to change Group-Separator to _ above, because in Role – group mapping for active directory, you must put the FQDN, which includes commas. Put an underscore separated list of FQDNS for each of these fields you want.

Track and log unclean shutdowns in CentOS 7

I needed to find a way to track if my CentOS 7 systems reboot unexpectedly. I was surprised that this isn’t something that the OS does by default. I found this article from RedHat that outlines that you basically have to write a couple of systemd scripts yourself if you want this functionality. So, I did.

I ended up with three separate systemd services that accomplish what I want:

  • set_graceful_shutdown: Runs just before shutdown. Creates a file /root/grateful_shutdown
  • log_ungraceful_shutdown: Runs on startup. Checks to see if /root/grateful_shutdown is missing and logs this fact to a file (/var/log/shutdown.log) if it is.
  • reset_shutdown_flag: Runs after log_ungraceful_shutdown. It checks for the presence of that file, and if it exists, removes it.

I placed these three files into /etc/systemd/system and then ran systemctl daemon-reload & systemctl enable for each one.


Description=Set flag for graceful shutdown

ExecStart=/bin/touch /root/graceful_shutdown



Description=Log ungraceful shutdown

ExecStart=/bin/sh -c "echo $$(date): Improper shutdown detected >> /var/log/shutdown.log"



Description=Check if previous system shutdown was graceful

ExecStart=/bin/rm /root/graceful_shutdown


It feels like a kludge but it works pretty well. The result is I get an entry in a log file if the system wasn’t shut down properly.

Linux Samba shares using Kerberos / AD credentials

I had a hell of a time trying to figure out why after upgrading the CentOS Samba package the samba shares quit working. Every time someone tried to access the share, the smb service would crash. I had this system configured to use active directory credentials and it worked well for a time, but no longer.

After much digging I found my problem to be the lack of a krb5.keytab file. This is due to my using PowerBroker Open instead of kerberos for authentication.

The solution was to add this line to my samba config:

kerberos method = system keytab

That one bit made all the difference. My current samba config is as follows with no more crashing: (Updated 8/29 to add workgroup name)

     security = ADS
     passdb backend = tdbsam
     realm = DOMAIN
     workgroup = NETBIOS_DOMAIN_NAME
     encrypt passwords = yes
     lanman auth = no
     ntlm auth = no
     kerberos method = system keytab
     obey pam restrictions = yes
     winbind enum users = yes
     winbind enum groups = yes

Update 8/29/2018: After updating and rebooting my smb service refused to start. It kept giving this very unhelpful message:

create_local_token failed: NT_STATUS_NO_MEMORY
ERROR: failed to setup guest info.
smb.service: main process exited, code=exited, status=255/n/a
Failed to start Samba SMB Daemon.

I couldn’t find any documentation on this and eventually resorted to just messing around with my smb.conf file. What fixed it was adding this to my configuration:


Replacing NETBIOS_DOMAIN_NAME with the old NetBIOS style domain name (what you would put in the domain part of domain\username for logging in) for my company. It worked!

Fix USB bluetooth in KDE Plasma on CentOS 7

I spent too many hours trying to figure this stupid thing out.. but FINALLY! I have my bluetooth headset working in CentOS 7 with the KDE 4 Plasma environment. Read on if you dare…

First, you must configure dbus to allow your user to use the bluetooth dongle. Add the following above the closing /busconfig tag.  Be sure to replace USERNAME with your user account:

sudo nano /etc/dbus-1/system.d/bluetooth.conf
  <policy user="USERNAME">
    <allow send_destination="org.bluez"/>
    <allow send_interface="org.bluez.Agent1"/>
    <allow send_interface="org.bluez.GattCharacteristic1"/>
    <allow send_interface="org.bluez.GattDescriptor1"/>
    <allow send_interface="org.freedesktop.DBus.ObjectManager"/>
    <allow send_interface="org.freedesktop.DBus.Properties"/>

Remove and re-plug the adapter in.

Next, follow Arch Linux’s excellent guide on how to pair a bluetooth device using bluetoothctl

[bluetooth]# power on
[bluetooth]# agent on
[bluetooth]# default-agent
[bluetooth]# scan on

Now make sure that your headset is in pairing mode. It should be discovered shortly. For example,

[NEW] Device 00:1D:43:6D:03:26 Lasmex LBT10

shows a device that calls itself “Lasmex LBT10” and has MAC address “00:1D:43:6D:03:26”. We will now use that MAC address to initiate the pairing:

[bluetooth]# pair 00:1D:43:6D:03:26

After pairing, you also need to explicitly connect the device (every time?):

[bluetooth]# connect 00:1D:43:6D:03:26

If you’re getting a connection error org.bluez.Error.Failed retry by killing existing PulseAudio daemon first:

$ pulseaudio -k
[bluetooth]# connect 00:1D:43:6D:03:26

Finally, configure pulseaudio to automatically switch all audio to your headset by adding the following line to the bottom of /etc/pulse/default.pa:

nano /etc/pulse/default.pa

# automatically switch to newly-connected devices
load-module module-switch-on-connect

Update 7/27: I rebooted my machine and lost my bluetooth, to my dismay. I discovered that my user needs to be a member of the audio group. Since I’m in an active directory environment I think the local audio group got removed at reboot. So, to restore it, as root I had to run this:

usermod -aG audio <user>

After doing that, to prevent logging out and back in again, you can do the following:


Once that’s done all the bluetoothctl commands worked again.