Logging in DSS


DSS processes write their log files to directory DATADIR/run:

Log file Content
backend.log Logs of the main DSS process (backend). This includes logs for all user operations directly performed in DSS, including through APIs. Training sessions in Visual analysis are also included in this log file.
hproxy.log Hadoop connectivity process (hproxy, optional)
nginx.log General log of the main HTTP server (nginx). This does not include the trace of user activity
nginx/access.log Access log of the main HTTP server (nginx)
ipython.log Logs of the Jupyter server, used by Python, R and Scala notebook.
supervisord.log Process control and supervision. This log file contains traces of all processes starts / stops
frontend.log Logs of Javascript activity on user’s browsers

Customizing log levels

The main processes in DSS use the log4j library for logging. You can configure the log level:

  • By logger (logging category)
  • By process

In a typical DSS log line:

[2017/02/13-09:01:01.421] [DefaultQuartzScheduler_Worker-1] [INFO] [dku.projects.stats.git]  - [ct: 365] Analyzing 17 commits

The logger is the 4th component: dku.projects.stats.git

Log levels are configured by creating, in the DSS data dir, a file named resources/logging/dku-log4j.properties

# Set, for all processes, the 'dku.recipes.sql' logger to INFO level.
# Note that this also sets INFO for all subloggers of dku.recipes.sql
log4j.logger.dku.recipes.sql = INFO

Properties set in dku-log4j.properties will apply to all main DSS processes (See The different Java processes for more information)

To set log levels only for a certain type of processes, like jek, create a file named resources/logging/dku-jek-log4j.properties and add the same kind of properties

Configuring log file rotation

Main DSS processes log files

By default, the “main” log files are rotated when they reach a given size, and purged after a given number of rotations. The following installation configuration directives can be used to customize this behavior.

By default, rotation happens every 50 MB and 10 files are kept

# Maximum file size, default 50MB.
# Suffix multipliers "KB", "MB" and "GB" can be used in this value.
# Define as 0 to disable automatic log file rotation.
logfiles_maxbytes = SIZE
# Number of retained files, default 10.
logfiles_backups = NUMBER_OF_FILES

You should then regenerate DSS configuration and restart DSS, as described in Installation configuration file.

This procedure applies to the following log files:

  • backend.log
  • hproxy.log
  • ipython.log
  • nginx.log


This is a low-level log for debug purposes only. It is rotated independently of the others, on a non-configurable schedule.


This file is rotated daily, whatever its size. The rotated file is compressed. Older files are then purged, in order to keep a total max size of logs below 64 MB

In the ini file, you can override this behavior

# Set this to false to disable access.log rotation
rotate_accesslog = true

# Maximum cumulative size to keep (in bytes). Suffix multipliers are not allowed
accesslog_purge_size = 67108864

Manual log file rotation

The following command forces DSS to close and reopen its log files (main DSS processes log files and nginx access log). Combined with standard tools like logrotate(8), and the possibility to disable automatic log rotation as described above, this lets you take full control over the DSS log rotation process, and integrate it in your log file handling framework.

# Use standard Unix commands to rename DSS current log files
# Force DSS to reopen new log files
DATADIR/bin/dss reopenlogs