Error messages

This section describes the most common 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)'

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.


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 between7:00AM and8:00AM or between16:00PM and17:00PM when your users log in or log off and that generates a lot of messages within a short interval.

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'

This message indicates that the other (remote) side could not verify the certificate sent by syslog-ng.


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

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 ^M characters as shown in the image below:

  • On Windows, save the certificate using UTF-8, for example, using Notepad++.

    Windows Notepad is not able to save the file in normal UTF-8, even if you select it.

    1. In Notepad++, from the menu, selectEncoding.

    2. Change the value fromUTF-8-BOMtoUTF-8.

    3. Save.

  • On Linux, run dos2unix cert.pem. This will convert the file to a Linux-compatible style.

    Alternatively, replace the EOL characters in the file manually.