7.4. file: Storing messages in plain-text files

The file driver is one of the most important destination drivers in syslog-ng. It allows to output messages to the specified text file, or to a set of files.

The destination filename may include macros which get expanded when the message is written, thus a simple file() driver may create several files: for example, syslog-ng OSE can store the messages of client hosts in a separate file for each host. For more information on available macros see Section 11.1.5, Macros of syslog-ng OSE.

If the expanded filename refers to a directory which does not exist, it will be created depending on the create-dirs() setting (both global and a per destination option).

The file() has a single required parameter that specifies the filename that stores the log messages. For the list of available optional parameters, see Section 7.4.1, file() destination options.

Declaration: 

file(filename options());
Example 7.11. Using the file() driver
destination d_file { file("/var/log/messages"); };
Example 7.12. Using the file() driver with macros in the file name and a template for the message
destination d_file {
        file("/var/log/${YEAR}.${MONTH}.${DAY}/messages"
             template("${HOUR}:${MIN}:${SEC} ${TZ} ${HOST} [${LEVEL}] ${MESSAGE}\n")
             template-escape(no));
};
Note

When using this destination, update the configuration of your log rotation program to rotate these files. Otherwise, the log files can become very large.

Also, after rotating the log files, reload syslog-ng OSE using the syslog-ng-ctl reload command, or use another method to send a SIGHUP to syslog-ng OSE.

Warning

Since the state of each created file must be tracked by syslog-ng, it consumes some memory for each file. If no new messages are written to a file within 60 seconds (controlled by the time-reap() global option), it is closed, and its state is freed.

Exploiting this, a DoS attack can be mounted against the system. If the number of possible destination files and its needed memory is more than the amount available on the syslog-ng server.

The most suspicious macro is ${PROGRAM}, where the number of possible variations is rather high. Do not use the ${PROGRAM} macro in insecure environments.