---
title: Application log files
---

Each Deephaven application process writes log files to disk. These log files contain general information, errors, and other application messages for each process. The log files are in plain text format and can be viewed or searched using standard text processing utilities.

## Log file locations

By default, the most recent application log files for Deephaven processes can be found in the following location:

`/var/log/deephaven/<Application Log Directory>/<Log Prefix>.log.current`

where the Application Log Directory and Log Prefix are different for each application.

For example, to view the current log file for the Authentication Server:

```bash
cat /var/log/deephaven/authentication_server/AuthenticationServer.log.current
```

These log locations are defined by properties in [Deephaven property files](../../configuration/deephaven-properties-overview.md) and can be changed. The root logging directory is defined by the `logroot` property, which has the following default value:

`logroot=/var/log/deephaven`

Each process can define its own log directory, using the form `logDir.<process name>=<log directory>`, and allowing the `<logroot>` substitution to use the `logroot` definition as a starting directory. For example, the following property defines the authentication server's log directory:

`logDir.authentication_server=<logroot>/authentication_server`

The following property defines a default log directory for process names which don't have their own definitions:

`defaultLogDir=<logroot>/misc`

The location can be changed by passing the `logDir` parameter into the JVM when a process is started. For example, passing the following parameter to a process changes the application log file location to the defined value:

`-DlogDir=/db/TempFiles/logs`

## Monitor application logs

A new log file is created every 15 minutes for each application. Every application also hard links a `.current` file to the current log file. The initial log file has a timestamp matching the time the process is started. Subsequent log files have the 15-minute timestamp interval.

The actual log file name has a timestamp suffix. For example, the Authentication Server log files:

`AuthenticationServer.log.2018-01-30-170000.000+0000`

Over a one-hour period, the Authentication Server will create four log files:

```
AuthenticationServer.log.2018-01-30-170000.000+0000
AuthenticationServer.log.2018-01-30-171500.000+0000
AuthenticationServer.log.2018-01-30-173000.000+0000
AuthenticationServer.log.2018-01-30-174500.000+0000
```

> [!NOTE]
> If a process crashes, its log file timestamp will not end with the `000+0000` suffix.

Common practice is to monitor the `.current` log file with `tail`. Be sure to use the `-F` option to ensure retries when a new log file is created:

```bash
cd /var/log/deephaven/authentication_server
tail -F AuthenticationServer.log.current
```

## Related documentation

- [Log files overview](./log-files.md)
- [Binary log files](./binary-logs.md)
- [Database event logs](./db-event-logs.md)