Rename the hostname in syslog-ng

At present, the syslog-ng (syslog-ng Open Source Edition) does not support to set the hostname of the server in the configuration. syslog-ng uses DNS system to resolve the system name or if it is explicitly switch off (with couple of options) it will use the IP. Sometimes the DNS name of the system may be not valid, for example in containers, or just for better naming purposes it is useful to have just a simple option to set the system’s hostname in the syslog packets.

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rewrite rule

The easiest and best way to change the system’s hostname in the packets is to use substitution rules with rewrite. In fact, the rewrite rule may operate on soft parts of the macros like MESSAGE, PROGRAM, HOST or user defined macros. The syslog message format and its “fields” could be seen in the RFC5424. It’s worth adding it is possible to replace the whole macro or just part of it.
Here is the configuration to set the system’s hostname:

#substitution rule
rewrite my_host { set("my-server-name", value("HOST")); };

#use the rule before the destination!!!
log { source(src); rewrite(my_host); destination(messages);};

The substitution rule should be used before the destination rule to take effect.

Here is a more complex example to set the system’s hostname only to certain packets:
Keep on reading!