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Debug your Linux DCV session

NICE DCV is a high-performance remote display protocol. It lets you securely deliver remote desktops and application streaming from any cloud or data center to any device, over varying network conditions. Official documentation can be found here.

How DCV is integrated to SOCA

1 - User creates a Windows or Linux DCV session via SOCA web interface

2 - SOCA executes a couple of actions via this function:

3 - Cloudformation will launch a EC2 instance and apply DCV related tags such as soca:NodeType=dcv, soca:DCVSessionUUID and soca:DCVSystem

3 - is a script running every minute on the scheduler. This script is responsible to update the Load Balancer with the new DCV instance as well as clean old/un-used load balancer rules. Log can be found under /apps/soca/$SOCA_CONFIGURATION/cluster_manager/

4 - Every time you access your DCV portal, SOCA will query the database and retrieve your associated DCV information from the database. To determine if your session is alive, a cURL command will be executed to the DCV host. Based on the return code, the database entry will be updated and your session state can take the following values:

  • state=running if the curl command return 200

  • state=stopped when you stop a running DCV session

  • state=impaired if the ec2-describe-instance determine your EC2 instance is not reachable

  • state=pending If the DCV session was created or restarted but the cURL command is not returning an HTTP/200 yet

For more information, refer to file or if yo uare debugging a Windows DCV

Understand what service is failing

It's recommended to run cURL -k -I (uppercase i) on DCV session and look for the headers returned to understand what to look for:

# curl -k -I https://<SOCA_URL><TOKEN>#<SESSION_ID>
HTTP/2 200
date: Fri, 13 Aug 2021 19:56:12 GMT
content-type: text/html; charset="utf-8"
content-length: 439
server: dcv
x-frame-options: DENY
strict-transport-security: max-age=31536000; includeSubDomains

server=dcv: Application Load Balancer (ALB) and DCV service are operating correctly, however your DCV session is not reachable. Refer to the Debug section below to understand why your DCV service is not operating correctly

# curl -k -I https://<SOCA_URL><TOKEN>#<SESSION_ID>
HTTP/2 502
server: awselb/2.0
date: Fri, 13 Aug 2021 20:00:08 GMT
content-type: text/html
content-length: 122

server=awselb/2.0: Either your ALB is not configured correctly or the DCV service is not running on the DCV host

Verify your CloudFormation stack is created correctly

Once you have triggered your virtual desktop via SOCA web interface, verify that your CloudFormation stack is created correctly.

Now that you confirmed CloudFormation stack has been created successfully, make sure the EC2 instance associated to the stack is up and running. Make sure your instance is in running state and Status check is 2/2


CloudFormation stack name and Instance name will always be soca-<CLUSTER_NAME>-<SESSION_NAME>-<SESSION_OWNER>

Verify the EC2 instance has been added to the load balancer correctly

Retrieve the private IP of your DCV host then navigate to EC2 Console > Load Balancing > Target Groups. Search for soca-ip-x-x-x-x where x-x-x-x is the private IP of your DCV host. Click "Targets" and make sure your DCV instance is registered successfully with a healthy state.

If you do not see the target group, refer to /apps/soca/$SOCA_CONFIGURATION/cluster_manager/ and review any error messages

Verify the Application Load Balancer (ALB) is updated correctly

Now that you have validated the target group, navigate to your ALB. Load balancer name will always be soca-<CLUSTER_NAME>-viewer. Once located, click "Listeners" tab then "View/Edit" rules for the HTTPS:443 listener.

Verify you have a new ALB rule named /ip-x-x-x-x (where x-x-x-x is the private IP of the DCV host) pointing to the target group created for your instance.

If you do not see the ALB rule, refer to /apps/soca/$SOCA_CONFIGURATION/cluster_manager/ and review any error messages.

Debug your Linux DCV session

You can find Linux DCV logs on /apps partition under /apps/soca/$SOCA_CONFIGURATION/cluster_node_boostrap/logs/desktop/<USER_NAME>/<SESSION_NAME>/<DCV_HOST>/.


If you delete a DCV session and recreate a new one with the same name, a new <DCV_HOST> directory will be created.

ls /apps/soca/$SOCA_CONFIGURATION/cluster_node_bootstrap/logs/desktop/mickael/LinuxDesktop1/ip-50-0-159-130/

What if I don't see the folder log?

If /apps/soca/$SOCA_CONFIGURATION/cluster_node_boostrap/logs/desktop/<USER_NAME>/<SESSION_NAME>/<DCV_HOST>/ is not created, then most likely something is wrong with the EC2 user data executed on the DCV host. Use SSM to connect to the host if you cannot SSH to the DCV host via its private IP.

Once you are connected to the ssh shell, sudo as root and navigate to /root/. Make sure all required packages are there:

[root@ip-50-0-159-130 ~]# ls -ltr
total 14136
drwxr-xr-x  2 3925172 users     4096 Apr 12 15:34 nice-dcv-2021.0-10242-el7-x86_64
-rw-r--r--  1 root    root  10762563 Apr 12 15:34 nice-dcv-2021.0-10242-el7-x86_64.tgz
-rw-r--r--  1 root    root      5375 Aug 12 18:44 config.cfg
-rw-r--r--  1 root    root   3686531 Aug 12 18:46 v20.0.1.tar.gz
drwxrwxr-x 13 root    root      4096 Aug 12 18:46 openpbs-20.0.1
-rw-r--r--  1 root    root      3406 Aug 12 18:48 open_ssl_ldap

Check if /apps and /data partitions are mounted correctly

[root@ip-50-0-159-130 ~]# df -h
Filesystem                                 Size  Used Avail Use% Mounted on
devtmpfs                                   3.8G     0  3.8G   0% /dev
tmpfs                                      3.8G     0  3.8G   0% /dev/shm
tmpfs                                      3.8G  860K  3.8G   1% /run
tmpfs                                      3.8G     0  3.8G   0% /sys/fs/cgroup
/dev/nvme0n1p1                              10G  3.9G  6.2G  39% /  8.0E  3.0M  8.0E   1% /data  8.0E  1.2G  8.0E   1% /apps
tmpfs                                      777M   28K  777M   1% /run/user/21245
tmpfs                                      777M     0  777M   0% /run/user/0

Debug EC2 User Data

If something is wrong, check te following logs to retrieve any potential errors during the initial execution:

  • /var/log/cloud-init

  • /var/log/cloud-init-output

  • /var/log/messages

An easy way to make retrieve any user-data error is to run cat /var/log/messages | grep cloud-init.

Manually interact with DCV

If the DCV system seems ok, verify that your DCV session is up and running by running dcv list-sessions.

dcv list-sessions
Session: '79e5feb7-b36d-48f4-b630-42753788d375' (owner:mickael type:virtual)

If you do not see any session, run dcv create-session --owner <USER_NAME> --storage-root "/data/home/<USER_NAME>/storage-root" <DCV_SESSION_ID> where <DCV_SESSION_ID> is the ID of your session that you can retrieve via the web ui.

Check for any logs under /var/log/dcv/ if you get any errors during your session creation

Verify DCV autostart after reboot

Sudo as the DCV user then run crontab -l to confirm the crontab is active

[root@ip-50-0-159-130 ~]# sudo su mickael
[mickael@ip-50-0-159-130 root]$ crontab -l
@reboot dcv create-session --owner mickael --storage-root "/data/home/mickael/storage-root" 79e5feb7-b36d-48f4-b630-42753788d375 # Do Not Delete

Debug your Windows DCV session

DCV is installed on Windows via EC2 User-Data. Once your EC2 host is up and running, use SSM to connect the EC2 instance to open a powershell environment. Instance name will always be soca-<CLUSTER_NAME>-<SESSION_NAME>-<SESSION_OWNER>. Make sure your instance is in running state and Status check is 2/2

# Run this command to get the EC2 UserData log
Get-Content C:\ProgramData\Amazon\EC2-Windows\Launch\Log\UserdataExecution.log

# Run this command to get SOCA related log
Get-Content C:\ProgramData\Amazon\EC2-Windows\Launch\Log\UserdataExecutionSOCA.log

You can also verify the different registry entry configured for DCV.

# SOCA Bootstrap will set custom Regedit such as:
New-ItemProperty -Path "Microsoft.PowerShell.Core\Registry::\HKEY_USERS\S-1-5-18\Software\GSettings\com\nicesoftware\dcv\security" -Name "auth-token-verifier" -PropertyType "String" -Value "https://%SOCA_SchedulerPrivateIP%/api/dcv/authenticator" -Force

# To verify the value, run Get-ItemProperty followed by the path name
Get-ItemProperty -Path "Microsoft.PowerShell.Core\Registry::\HKEY_USERS\S-1-5-18\Software\GSettings\com\nicesoftware\dcv\security"

Refer to the EC2 data script to get a list of all registry entries.

Also verify your DCV session is up and running

# Verify if dcvserver is up and running
PS C:\Windows\system32> Get-Service dcvserver

Status   Name               DisplayName
------   ----               -----------
Running  dcvserver          DCV Server

# Verify if your session is active via "dcv.exe describe-session console"
PS C:\Windows\system32> & 'C:\Program Files\NICE\DCV\Server\bin\dcv.exe' describe-session console
        id: console
        owner: mickael
        display layout: 1280x1024+0+0

Retrieve your DCV information on the database

Connect to the scheduler instance and sudo as root user and run sqlite3 /apps/soca/$SOCA_CONFIGURATION/cluster_web_ui/db.sqlite

# sqlite3 /apps/soca/$SOCA_CONFIGURATION/cluster_web_ui/db.sqlite
SQLite version 3.7.17 2013-05-20 00:56:22
Enter ".help" for instructions
Enter SQL statements terminated with a ";"

Type .tables to list all SOCA SQL tables. DCV sessions information are stored under windows_dcv_sessions and linux_dcv_session

sqlite> .tables 

You can now run your own SQL queries to retrieve all data (select * from linux_dcv_sessions;) or use more complex queries such as:

-- Return all active Linux session for user
select * from linux_dcv_sessions where user="<USER>" and is_active=1;

-- Return all inactive Linux sessions
select * from linux_dcv_sessions where is_active=0;

-- Return specific session 
select * from linux_dcv_sessions where tag_uuid="79e5feb7-b36d-48f4-b630-42753788d375";

-- Return all sessions that have schedule disabled for saturday
select * from linux_dcv_sessions where schedule_saturday_start=0 and schedule_saturday_stop=0;

SQL Schema

Column names can be found on

Most Common Errors

Custom Python environment

You must use Python provided by the system by default. This issue usually happen when you installed tools such as Anaconda3 which override the default profile and configure Anaconda3's Python environment as default. To verify what version of Python you are using, run which python3

# Invalid Python, your DCV session will not start
$ which python3

# Correct Python environment
$ which python3

To fix this issue, edit your .bash_profile or .bash_rc and make sure your PATH is updated correctly

# Incorrect Path as Anaconda3 will override the default Python
export PATH=/apps/anaconda3/bin:$PATH

# Correct Path.
export PATH=$PATH:/apps/anaconda3/bin