syslog-ng Open Source Edition 3.20 - Administration Guide

Error messages

Destination queue full

Destination queue full, dropping messages; queue_len='10000', 
log_fifo_size='10000', count='4', 
persist_name='afsocket_dd_qfile(stream,serverdown:514)' 

Alert unknown CA

SSL error while writing stream; tls_error='SSL routines:ssl3_read_bytes:tlsv1 alert unknown ca'

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^Mcharacters as shown in the image below: Figure 20: Example of OpenSSL character processing error
Solution:	On Windows, save the certificate using UTF-8, for example, using Notepad++. NOTE: Windows Notepad is not able to save the file in normal UTF-8, even if you select it. In Notepad++, from the menu, selectEncoding. Change the value fromUTF-8-BOMtoUTF-8. 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.

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.

• 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.

• 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.

Handling large message load

This section provides tips on optimizing the performance of syslog-ng. Optimizing the performance is important for syslog-ng hosts that handle large traffic.

• Disable DNS resolution, or resolve hostnames locally. For details, see Using name resolution in syslog-ng.

• Enable flow-control for the TCP sources. For details, see Managing incoming and outgoing messages with flow-control.

• Do not use the usertty() destination driver. Under heavy load, the users are not be able to read the messages from the console, and it slows down syslog-ng.

• Do not use regular expressions in our filters. Evaluating general regular expressions puts a high load on the CPU. Use simple filter functions and logical operators instead. For details, see Regular expressions.

• Caution: When receiving messages using the UDP protocol, increase the size of the UDP receive buffer on the receiver host (that is, the syslog-ng OSE server or relay receiving the messages). Note that on certain platforms, for example, on Red Hat Enterprise Linux 5, even low message load (~200 messages per second) can result in message loss, unless the so-rcvbuf() option of the source is increased. In such cases, you will need to increase the net.core.rmem_max parameter of the host (for example, to 1024000), but do not modify net.core.rmem_default parameter. As a general rule, increase the so-rcvbuf() so that the buffer size in kilobytes is higher than the rate of incoming messages per second. For example, to receive 2000 messages per second, set the so-rcvbuf() at least to 2 097 152 bytes.

• Increase the value of the flush-lines() parameter. Increasing flush-lines() from 0 to 100 can increase the performance of syslog-ng OSE by 100%.