Using syslog facility to log to custom file

[ozcanay]

I am trying to write to "custom_file.log" file in /var/log directory. My OS is CentOS. What I have tried to far:

Adding line

local2.* /var/log/custom_file.log

to "/etc/rsyslog.conf" file. Then entering command "sudo service rsyslog restart" to restart rsyslog.

After that, I am just using the most basic example for syslog facility of spdlog:

std::string ident = "spdlog-example";
auto syslog_logger = spdlog::syslog_logger_mt("syslog", ident, LOG_LOCAL2);
syslog_logger->warn("This is warning that will end up in syslog.");

Note that I am using LOG_LOCAL2 syslog facility here. However, the message won't be printed to "/var/log/custom_file.log".
If I change LOG_LOCAL2 to LOG_PID, the message will be printed to "/var/log/messages".

To see if LOG_LOCAL2 facility is not at fault, I tried logging via Linux syscalls:

#define open_log(str) do {                                                             \
    openlog(str, LOG_CONS | LOG_NDELAY, LOG_LOCAL2);                                   \
} while(0)

#define info_log(str, ...) do {                                                        \
    syslog(LOG_INFO, str,  ##__VA_ARGS__);                                             \
} while(0)

int main()
{
    open_log("config");

    info_log("TEST1");
    info_log("TEST2");
    info_log("TEST3");
}

This works as intended.

So, my question is, first of all, is it possible to write to a custom log file via spdlog. If so, where exactly am I wrong here?

[tt4g]

First of all, I don't usually use syslog, so I may be guiding you wrongly.

Looking at the function declaration, it is the fourth argument of spdlog::syslog_logger_mt() that corresponds to the third argument facility of openlog().

spdlog/include/spdlog/sinks/syslog_sink.h

Lines 95 to 101 in eb32206

	// Create and register a syslog logger
	template<typename Factory = spdlog::synchronous_factory>
	inline std::shared_ptr<logger> syslog_logger_mt(const std::string &logger_name, const std::string &syslog_ident = "", int syslog_option = 0,
	int syslog_facility = LOG_USER, bool enable_formatting = false)
	{
	return Factory::template create<sinks::syslog_sink_mt>(logger_name, syslog_ident, syslog_option, syslog_facility, enable_formatting);
	}

spdlog/include/spdlog/sinks/syslog_sink.h

Lines 24 to 37 in eb32206

	syslog_sink(std::string ident, int syslog_option, int syslog_facility, bool enable_formatting)
	: enable_formatting_{enable_formatting}
	, syslog_levels_{{/* spdlog::level::trace */ LOG_DEBUG,
	/* spdlog::level::debug */ LOG_DEBUG,
	/* spdlog::level::info */ LOG_INFO,
	/* spdlog::level::warn */ LOG_WARNING,
	/* spdlog::level::err */ LOG_ERR,
	/* spdlog::level::critical */ LOG_CRIT,
	/* spdlog::level::off */ LOG_INFO}}
	, ident_{std::move(ident)}
	{
	// set ident to be program name if empty
	::openlog(ident_.empty() ? nullptr : ident_.c_str(), syslog_option, syslog_facility);
	}

A should be specified as the fourth argument.

std::string ident = "spdlog-example";
auto syslog_logger = spdlog::syslog_logger_mt("syslog", ident, LOG_CONS | LOG_NDELAY, LOG_LOCAL2);
syslog_logger->warn("This is warning that will end up in syslog.");

[ozcanay]

Yeah, that was my bad. Thanks for the help!

spdlog::syslog_logger_mt("syslog", "config-manager", LOG_CONS | LOG_NDELAY, LOG_LOCAL2);

works well.