The syslog-ng application can resolve the hostnames of the clients and include them in the log messages. However, the performance of syslog-ng is severely degraded if the domain name server is unaccessible or slow. Therefore, it is not recommended to resolve hostnames in syslog-ng. If you must use name resolution from syslog-ng, consider the following:
-
Use DNS caching. Verify that the DNS cache is large enough to store all important hostnames. (By default, the syslog-ng DNS cache stores 1007 entries.)
options { dns-cache-size(2000); };
-
If the IP addresses of the clients change only rarely, set the expiry of the DNS cache large.
options { dns-cache-expire(87600); };
-
If possible, resolve the hostnames locally. For details, see Procedure 20.1, “Resolving hostnames locally”.
|
|
NOTE:
Domain name resolution is important mainly in relay and server mode. |
Procedure 20.1. Resolving hostnames locally
Purpose:
Resolving hostnames locally enables you to display hostnames in the log files for frequently used hosts, without having to rely on a DNS server. The known IP address – hostname pairs are stored locally in a file. In the log messages, syslog-ng will replace the IP addresses of known hosts with their hostnames. To configure local name resolution, complete the following steps:
Steps:
-
Add the hostnames and the respective IP addresses to the file used for local name resolution. On Linux and UNIX systems, this is the /etc/hosts file. Consult the documentation of your operating system for details.
-
Instruct syslog-ng to resolve hostnames locally. Set the use-dns() option of syslog-ng to persist_only.
-
Set the dns-cache-hosts() option to point to the file storing the hostnames.
options {
use-dns(persist_only);
dns-cache-hosts(/etc/hosts); };
The syslog-ng PE application does not rotate logs by itself. To use syslog-ng PE for log rotation, consider the following approaches:
Use logrotate together with syslog-ng PE:
-
Ideal for workstations or when processing fewer logs.
-
It is included in most distributions by default.
-
Less scripting is required, only logrotate has to be configured correctly.
-
Requires frequent restart (syslog-ng PE must be reloaded/restarted when the files are rotated). After rotating the log files, reload syslog-ng PE using the syslog-ng-ctl reload command, or use another method to send a SIGHUP to syslog-ng PE.
-
The statistics collected by syslog-ng PE, and the correlation information gathered with Pattern Database is lost with each restart.
Separate incoming logs based on time, host or other information:
-
Ideal for central log servers, where regular restart of syslog-ng PE is unfavorable.
-
Requires shell scripts or cron jobs to remove old logs.
-
It can be done by using macros in the destination name (in the filename, directory name, or the database table name).
Example 20.1. File destination for log rotation
This sample file destination configuration stores incoming logs in files that are named based on the current year, month and day, and places these files in directories that are named based on the hostname:
destination d_sorted { file("/var/log/remote/${HOST}/${YEAR}_${MONTH}_${DAY}.log" create-dirs(yes)); };
Example 20.2. Logstore destination for log rotation
This sample logstore destination configuration stores incoming logs in logstores that are named based on the current year, month and day, and places these logstores in directories that are named based on the hostname:
destination d_logstore { logstore("/var/log/remote/${HOST}/${YEAR}_${MONTH}_${DAY}.lgs" compress(9) create-dirs(yes)); };
Example 20.3. Command for cron for log rotation
This sample command for cron removes files older than two weeks from the /var/log/remote directory:
find /var/log/remote/ -daystart -mtime +14 -type f -exec rm {} \;
GNU General Public License v2
The licenses for most software are designed to take away your freedom to share and change it. By contrast, the GNU General Public License is intended to guarantee your freedom to share and change free software - to make sure the software is free for all its users. This General Public License applies to most of the Free Software Foundation's software and to any other program whose authors commit to using it. (Some other Free Software Foundation software is covered by the GNU Library General Public License instead.) You can apply it to your programs, too.
When we speak of free software, we are referring to freedom, not price. Our General Public Licenses are designed to make sure that you have the freedom to distribute copies of free software (and charge for this service if you wish), that you receive source code or can get it if you want it, that you can change the software or use pieces of it in new free programs; and that you know you can do these things.
To protect your rights, we need to make restrictions that forbid anyone to deny you these rights or to ask you to surrender the rights. These restrictions translate to certain responsibilities for you if you distribute copies of the software, or if you modify it.
For example, if you distribute copies of such a program, whether gratis or for a fee, you must give the recipients all the rights that you have. You must make sure that they, too, receive or can get the source code. And you must show them these terms so they know their rights.
We protect your rights with two steps:
-
copyright the software, and
-
offer you this license which gives you legal permission to copy, distribute and/or modify the software.
Also, for each author's protection and ours, we want to make certain that everyone understands that there is no warranty for this free software. If the software is modified by someone else and passed on, we want its recipients to know that what they have is not the original, so that any problems introduced by others will not reflect on the original authors' reputations.
Finally, any free program is threatened constantly by software patents. We wish to avoid the danger that redistributors of a free program will individually obtain patent licenses, in effect making the program proprietary. To prevent this, we have made it clear that any patent must be licensed for everyone's free use or not licensed at all.
The precise terms and conditions for copying, distribution and modification follow.
