Category Archives: OS

Add Ubuntu PPA key to Debian

Occasionally I want to install packages located at an Ubuntu PPA repository on my Debian stretch machine. There’s a bit of a trick to it, thanks to chrisjean.com for outlining what needs to be done.

Step 1 is the same as in Ubuntu, add the PPA with add-apt-repository (install if it’s not already there)

sudo add-apt-repository ppa:<contributor>/<ppa name>

This will appear to work but when you do an apt update you may get something similar to this

W: GPG error: http://ppa.launchpad.net/jonathonf/gcc-7.1/ubuntu xenial InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 8CF63AD3F06FC659
W: The repository 'http://ppa.launchpad.net/jonathonf/gcc-7.1/ubuntu xenial InRelease' is not signed.
N: Data from such a repository can't be authenticated and is therefore potentially dangerous to use.
N: See apt-secure(8) manpage for repository creation and user configuration details.

The last step is to manually import the key with the following command:

sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys <KEY_OF_PPA>

The PPA key will be listed on the PPA’s page. Once I ran that second command everything worked swimmingly.

Flatten nested AD group memberships with powershell

Several applications at my job do not know how to read nested security groups. This is annoying because we grant everything through security groups instead of individual entitlements.

I’ve recently finished writing a powershell script that will “flatten” a security group that has nested security groups. This script reads a security group’s membership, compares the individually assigned users with the nested security group membership, and then reconciles them so only members of the nested security group are individually added to the main group. It allows me to simply add a security group to another security group, and still be able to use the group to grant access to applications that don’t support nested groups. It also ensures that nobody has rogue access they shouldn’t have. Everything managed through groups like God intended.

I consulted a ton of different sites to accomplish this. Here are just a few:

https://www.reddit.com/r/PowerShell/comments/3f7iki/flatten_out_active_directory_groups_containing/

https://stackoverflow.com/questions/11526285/how-to-count-objects-in-powershell

https://stackoverflow.com/questions/41658770/determining-object-type

https://docs.microsoft.com/en-us/powershell/module/activedirectory/

https://ss64.com/ps/syntax-compare.htmlhttps://ss64.com/ps/compare-object.html

#Nested Security Group flattener script
#Written by Nicholas Jeppson, 10/6/2018

#This script scans nested security groups and compares their membership to that of the base security group.
#It then reconciles membership so that the only members of this group are those who are members of the nested security groups.
#This is required for applications that cannot read nested security groups, such as mattermost.
#No more manually adding people to a group after you've already added their role to that same group!

#=============Variables section=============#

#Enter groups to reconcile here, separated by quotes and a comma:
$groups_to_flatten = @("group1","group2")

#==========End Variables Section=============#

#Loop through each group to flatten
foreach ($group in $groups_to_flatten) {

    Write-Host "`nProcessing group ""$group"""

    #Read current individually added users
    $individually_added_users = get-ADGroupMember -Identity $group | Where-Object {$_.objectClass -eq 'user'}

    #Read group membership of nested groups - Ignore specific user (optional)
    $nested_group_members = get-ADGroupMember -Identity $group | Where-Object {$_.objectClass -eq 'group'} | Get-ADGroupMember -Recursive | Where-Object {$_.name -ne 'USER_TO_IGNORE'}

    #Compare current individually added users with that of nested security groups
    $users_to_add = Compare-Object -ReferenceObject $individually_added_users -DifferenceObject $nested_group_members -PassThru | Where-Object {$_.SideIndicator -eq "=>"}
    $users_to_remove = Compare-Object -ReferenceObject $individually_added_users -DifferenceObject $nested_group_members -PassThru | Where-Object {$_.SideIndicator -eq "<="}
    
    #loop through each user to remove and remove them
    foreach ($user in $users_to_remove) {
        Remove-ADGroupMember -Identity $group -Member $user -Confirm:$false
        Write-Host "Removed: $user"
    }
    
    #loop through each user to add and add them
    foreach ($user in $users_to_add) {
        #Add nested group membership individually back to the parent group
        #Write-Host "Adding individual members to ""$group""`n`n"
        Add-ADGroupMember -Identity $group -Members $user -Confirm:$false 
        Write-Host "Added: $user"   
    }
}

Make FreeDOS boot ISO to flash BIOS

I needed to flash the BIOS of one of my old server motherboards and to my dismay found the only way to do so was via DOS boot image. It was not straightforward so I thought I’d write it down. Thanks to pingtool & tummy.com for the information I needed to pull it off.

First, obtain a copy of FreeDOS ISO and extract it to a directory

  • mount -o loop <freedosISO.iso> <mount directory>
  • rsync -aP <mount directory> <directory you want files to copy to>

Next, copy the necessary flash utilities and firmware files to that same directory as above.

Lastly, use genisoimage to create a new ISO image based on the above folder. Modify -o output to wherever you want the ISO to go.

sudo apt install genisoimage
cd <folder you copied your files to>
mkisofs -o /tmp/freedos_biosupdate.iso -q -l -N \
   -boot-info-table -iso-level 4 -no-emul-boot \
   -b isolinux/isolinux.bin \
   -publisher "FreeDOS - www.freedos.org" \
   -A "FreeDOS beta9 Distribution" -V FDOS_BETA9 -v .

From here you can take the ISO and mount / burn it as needed. It will boot into FreeDOS. Tell it to go to a shell and away you go.

FreeNAS ZFS tuning for SSDs

I wanted to optimize my all SSD storage array on my FreeNAS server but I had a hard time finding information in one place. After a lot of digging I pulled things from several places. This is what I came up with. It boiled down to two main settings

  • ashift
  • recordsize

Checking ashift on existing pools

zdb -U /data/zfs/zpool.cache | grep ashift

I read here a recommended setting of ashift=13, recordsize=8k for VM workloads on SSDs.

How to change recordsize:

This is easily done in the GUI or command line and can be changed on the fly.

zfs set recordize <value> <volume>

How to change ashift:

Backup your data and destroy the pool.

Modify the setting dictating minimum ashift setting as outlined here

sysctl vfs.zfs.min_auto_ashift=13

Re-create the pool.

Additional reading

http://open-zfs.org/wiki/Performance_tuning#Alignment_shift
https://www.reddit.com/r/zfs/comments/7pfutp/zfs_pool_planning_for_vm_storage/

Free up RAM after Proxmox live migration

I ran into an issue where after migrating a bunch of VMs off of one of  my hosts, the remaining VMs on it refused to turn on. Every time I tried the command would hang for a while and eventually error out with this message

TASK ERROR: start failed: command '/usr/bin/kvm -id <truncated>... ' failed: got timeout

I suspected this might be due to RAM use and sure enough the usage was too high for a system that didn’t have any VMs running on it.  I found here that I could run a command to flush the cache:

echo 3 > /proc/sys/vm/drop_caches

That caused the RAM usage to go down but the symptom of the VM not starting remained. I then saw the KSM sharing still had some memory in it. I decided to restart the KSM sharing service:

sudo systemctl restart ksmtuned

After running that the VM started!

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.

set_graceful_shutdown.service

[Unit]
Description=Set flag for graceful shutdown
DefaultDependencies=no
RefuseManualStart=true
Before=shutdown.target

[Service]
Type=oneshot
ExecStart=/bin/touch /root/graceful_shutdown

[Install]
WantedBy=shutdown.target

log_ungraceful_shutdown.service

[Unit]
Description=Log ungraceful shutdown
ConditionPathExists=!/root/graceful_shutdown
RefuseManualStart=true
RefuseManualStop=true
Before=reset_shutdown_flag.service

[Service]
Type=oneshot
RemainAfterExit=true
ExecStart=/bin/sh -c "echo $$(date): Improper shutdown detected >> /var/log/shutdown.log"

[Install]
WantedBy=multi-user.target

reset_shutdown_flag.service

[Unit]
Description=Check if previous system shutdown was graceful
ConditionPathExists=/root/graceful_shutdown
RefuseManualStart=true
RefuseManualStop=true

[Service]
Type=oneshot
RemainAfterExit=true
ExecStart=/bin/rm /root/graceful_shutdown

[Install]
WantedBy=multi-user.target

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.

Clone AD Group Memberships with Powershell

I needed to do windoze administration today.  I dug my way into a hole and finally found my way out. Thanks to answers on Technet for the information I found a way to clone AD group membership from one group to another via powershell.

The command I settled on was the following (after creating the new group first)

Get-ADGroup -Identity "name_of_existing_group" -Properties MemberOf | foreach {$_.MemberOf} | foreach {add-ADGroupMember -Identity $_ -members "new_group_to_copy_memberOf_to" }

It grabs everything the group is a member of and transforms the output to a string array. It then takes that array and uses each item of it to add your new group as a member to everything the old group is a member of.

Mount encfs folder on startup with systemd

A quick note on how to encrypt a folder with encfs and then mount it on boot via a systemd startup script. In my case the folder is located on a network drive and I wanted it to happen whether I was logged in or not.

Create encfs folder:

encfs <path to encrypted folder> <path to mount decrypted folder>

Follow the prompts to create the folder and set a password.

Next create a file which will contain your decryption password

echo "YOUR_PASSWORD" > /home/user/super_secret_password_location
chmod 700 /home/user/super_secret_password_location

Create a simple script to be called by systemd on startup using cat to pass your password over to encfs

#!/bin/bash
cat super_secret_password_location | encfs -S path_to_encrypted_folder path_to_mount_decrypted_folder

Finally create a systemd unit to run your script on startup:

vim /etc/systemd/system/mount-encrypted.service
[Unit] 
Description=Mount encrypted folder 
After=network.target 

[Service] 
User=<YOUR USER> 
Type=oneshot 
ExecStartPre=/bin/sleep 20 
ExecStart=PATH_TO_SCRIPT
TimeoutStopSec=30 
KillMode=process 

[Install] 
WantedBy=multi-user.target

Then enable the unit:

sudo systemctl daemon-reload
sudo systemctl enable mountt-encrypted.service

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)

[global]
     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:

 ../source3/auth/auth_util.c:1399(make_new_session_info_guest)
create_local_token failed: NT_STATUS_NO_MEMORY
../source3/smbd/server.c:2011(main)
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:

workgroup = NETBIOS_DOMAIN_NAME

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"/>
  </policy>

Remove and re-plug the adapter in.

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


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:

su - <USERNAME>

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