Simple syslog-ng configuration for collecting everything in the system to logging to just a single destination file.

syslog-ng.conf

# Configuration file to replace `/etc/syslog-ng/syslog-ng.conf`
@version: 3.38
@include "scl.conf"

# Syslog-ng configuration file, compatible with default Debian syslogd
# installation.

# First, set some global options.
options {
    chain_hostnames(off);
    flush_lines(0);
    use_dns(yes);
    use_fqdn(no);
    dns_cache(yes);
    owner("root");
    group("adm");
    perm(0640);
    stats_freq(0);
    bad_hostname("^gconfd$");
    ts_format("iso");
};

########################
# Sources
########################
# This is the default behavior of sysklogd package
# Logs may come from unix stream, but not from another machine.
#
source s_src {
       system();
       internal();
       udp(ip(0.0.0.0) port(514));

       # systemd uses `/dev/log`, so we have to avoid that here. -_-
       unix-stream ("/dev/log");
       # Uncomment if you are running a systemd-loggerd.
       #systemd-syslog();
};

destination d_messages { file("/var/log/messages"); };
log { source(s_src); destination(d_messages); };

###
# Include all config files in /etc/syslog-ng/conf.d/
###
@include "/etc/syslog-ng/conf.d/*.conf"