If you need help, want to open a support ticket, or report a bug, we recommend using the syslog-debun tool to collect information about your environment and syslog-ng PE version. For details, see syslog-debun(1). For support, contact our Support Team.

Recover data from orphaned diskbuffer files

Chapter 19. Troubleshooting syslog-ng > Recover data from orphaned diskbuffer files

When you change the configuration of a syslog-ng PE host that uses disk-based buffering (also called disk queue), syslog-ng PE may start new disk buffer files for the destinations that you have changed. In such case, syslog-ng PE abandons the old disk queue files. If there were unsent log messages in the disk queue files, these messages remain in the disk queue files, and will not be sent to the destinations.

To find, examine, and flush the log messages from such orphaned disk queue files, see the Sending out messages stuck in syslog-ng disk queue files tutorial.

Chapter 20. 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 the section called “Using name resolution in syslog-ng”.

Procedure 20.2. Collecting logs from chroot

Purpose:

To collect logs from a chroot using a syslog-ng client running on the host, complete the following steps:

Figure 20.1. Collecting logs from chroot

Steps:

Create a /dev directory within the chroot. The applications running in the chroot send their log messages here.
Create a local source in the configuration file of the syslog-ng application running outside the chroot. This source should point to the /dev/log file within the chroot (for example to the /chroot/dev/log directory).
Include the source in a log statement.

NOTE:
You need to set up timezone information within your chroot as well. This usually means creating a symlink to /etc/localtime.

Handling large message load

Chapter 20. Best practices and examples > 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 the section called “Using name resolution in syslog-ng”.
Enable flow-control for the TCP sources. For details, see the section called “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 the section called “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 PE 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 PE by 100%.

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