No logs after specifying an unusual port number
Security-Enhanced Linux (SELinux) is a set of kernel and user-space tools enforcing strict access control policies. SELinux rules in Linux distributions cover all aspects of the syslog-ng configuration coming in the syslog-ng package available in the distribution. But as soon as an unusual port number or directory name is specified in the configuration, syslog-ng fails to work even with a completely legitimate configuration.
By default, SELinux only allows connections to the default syslog ports. When you have to use any other port for some reason, sending logs to that port will not work. For details on how to fix this issue, see section
Error messages
Destination queue full
| Error message: | Destination queue full, dropping messages; queue_len='10000', log_fifo_size='10000', count='4', persist_name='afsocket_dd_qfile(stream,serverdown:514)' |
| Description: |
This message indicates message loss. Flow-control must be enabled in the log path. When flow-control is enabled, syslog-ng will stop reading messages from the sources of the log statement if the destinations are not able to process the messages at the required speed. If flow-control is enabled, syslog-ng will only drop messages if the destination queues/window sizes are improperly sized. |
| Solution: |
Enable flow-control in the log path. If flow-control is disabled, syslog-ng will drop messages if the destination queues are full. Note that syslog-ng will drop messages even if the server is alive. If the remote server accepts logs at a slower rate than the sender syslog-ng receives them, the sender syslog-ng will fill up the destination queue, then drop the newer messages. Sometimes this error occurs only at a specific time interval, for example, only between For more information, see Managing incoming and outgoing messages with flow-control. |
Alert unknown CA
| Error message: | SSL error while writing stream; tls_error='SSL routines:ssl3_read_bytes:tlsv1 alert unknown ca' |
| Description: |
This message indicates that the other (remote) side could not verify the certificate sent by syslog-ng. |
| Solution: |
Check the logs on the remote site and identify why the receiving syslog-ng could not find the CA certificate that signed this certificate. |
PEM routines:PEM_read_bio:no start line
| Error message: | testuser@thor-x1:~/cert_no_start_line/certs$ openssl x509 -in cert.pem -text unable to load certificate 140178126276248:error:0906D06C:PEM routines:PEM_read_bio:no start line:pem_lib.c:701:Expecting: TRUSTED CERTIFICATE | ||
| Description: |
The error message is displayed when using Transport Layer Security (TLS). The syslog-ng application uses OpenSSL for TLS and this message indicates that the certificate contains characters that OpenSSL cannot process. The error occurs when the certificate comes from Windows and you want to use it on a Linux-based computer. On Windows, the end of line (EOL) character is different (\r\n) compared to Linux (\n). To verify this, open the certificate in a text editor, for example, MCEdit. Notice the
Figure 20: Example of OpenSSL character processing error 
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| Solution: |
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Best practices and examples
This chapter discusses some special examples and recommendations.
General recommendations
This section provides general tips and recommendations on using syslog-ng. Some of the recommendations are detailed in the subsequent sections.
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Do not base the separation of log messages into different files on the facility parameter. As several applications and processes can use the same facility, the facility does not identify the application that sent the message. By default, the facility parameter is not even included in the log message itself. In general, sorting the log messages into several different files can make finding specific log messages difficult. If you must create separate log files, use the application name.
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Standard log messages include the local time of the sending host, without any time zone information. It is recommended to replace this timestamp with an ISODATE timestamp, because the ISODATE format includes the year and timezone as well. To convert all timestamps to the ISODATE format, include the following line in the syslog-ng configuration file:
options {ts-format(iso) ; }; -
Resolving the IP addresses of the clients to domain names can decrease the performance of syslog-ng. For details, see Using name resolution in syslog-ng.