NXLog can be used to collect and process logs from a Linux system.
Linux distributions normally use a "Syslog" system logging agent to retrieve
events from the kernel (
/proc/kmsg) and accept log messages from user-space
/dev/log). Originally, this logger was syslogd; later
syslog‑ng added additional features, and finally Rsyslog is the logger in
common use today. For more information about Syslog, see Syslog.
Many modern Linux distributions also use the Systemd init system, which
includes a journal component for handling log messages. All messages generated
by Systemd-controlled processes are sent to the journal. The journal also
handles messages written to
/dev/log. The journal stores logs in a binary
format, either in memory or on disk; the logs can be accessed with the
journalctl tool. Systemd can also be configured to forward logs via a socket
to a local logger like Rsyslog or NXLog.
There are several ways that NXLog can be configured to collect Linux logs. See Replacing Rsyslog for details about replacing Rsyslog altogether, handling all logs with NXLog instead. See Forwarding Messages via Socket for a simple way to forward all logs to NXLog without disabling Rsyslog (this is the least intrusive option). Finally, it is also possible to read the log files written by Rsyslog; see Reading Rsyslog Log Files.
Follow these steps to disable Rsyslog and configure NXLog to collect logs in its place.
Configure NXLog to collect events from the kernel, the Systemd journal socket, and the
/dev/logsocket. See the example below.
Configure Systemd to forward log messages to a socket by enabling the
Stop and disable Rsyslog by running
systemctl stop rsyslogand
systemctl disable rsyslogas root.
Reload the journald configuration by running
systemctl force-reload systemd-journald.
This example configures NXLog to read kernel events with the
im_kernel module, read daemon messages from the Systemd journal
socket with the im_uds module, and accept other user-space messages
/dev/log socket with im_uds. In the om_tcp module
instance, all of the logs are converted to JSON format, BSD Syslog headers are
added, and the logs are forwarded to another host via TCP.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 <Extension _json> Module xm_json </Extension> <Extension _syslog> Module xm_syslog </Extension> <Input kernel> Module im_kernel Exec parse_syslog_bsd(); </Input> <Input journal> Module im_uds UDS /run/systemd/journal/syslog Exec parse_syslog_bsd(); </Input> <Input devlog> Module im_uds UDS /dev/log FlowControl FALSE Exec $raw_event =~ s/\s+$//; parse_syslog_bsd(); </Input> <Output out> Module om_tcp Host 192.168.1.1 Port 1514 Exec $Message = to_json(); to_syslog_bsd(); </Output> <Route r> Path kernel, journal, devlog => out </Route>
Some local Syslog sources will add a trailing newline (
By adding a short configuration file, Rsyslog can be configured to forward messages to NXLog via a Unix domain socket. This is the least intrusive of the options documented here.
Configure NXLog to accept log messages from Rsyslog via a socket. See the example below.
Configure Rsyslog to write to the socket by adding the following configuration file. See the Rsyslog documentation for more information about configuring what is forwarded to NXLog./etc/rsyslog.d/nxlog.conf
# Load omuxsock module $ModLoad omuxsock # Set socket path $OMUxSockSocket /opt/nxlog/var/spool/nxlog/rsyslog_sock # Configure template to preserve PRI part (must be on a single line) $template SyslogWithPRI,"<%PRI%>%timegenerated% %HOSTNAME% %syslogtag%%msg:::drop-last-lf%" # Forward all log messages *.* :omuxsock:;SyslogWithPRI # Only forward log messages of "notice" priority and higher #*.notice :omuxsock:;SyslogWithPRI
Restart NXLog and Rsyslog in that order to create and use the socket (NXLog must create the socket before Rsyslog will write to it). Run
systemctl restart nxlogand
systemctl restart rsyslog.
With this example configuration, NXLog will create the socket and accept log messages from Rsyslog through the socket. The messages will then be parsed as Syslog, converted to JSON format, prefixed with a BSD Syslog header, and forwarded to another host via TLS.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 <Extension _json> Module xm_json </Extension> <Extension _syslog> Module xm_syslog </Extension> <Input in> Module im_uds UDS /opt/nxlog/var/spool/nxlog/rsyslog_sock Exec parse_syslog(); </Input> <Output out> Module om_ssl Host 192.168.1.1 Port 6514 CAFile %CERTDIR%/ca.pem CertFile %CERTDIR%/client-cert.pem CertKeyFile %CERTDIR%/client-key.pem Exec $Message = to_json(); to_syslog_bsd(); </Output>
NXLog can be configured to read from log messages written by Rsyslog,
/var/log/messages for example. This is a slightly more intrusive option than
the steps given in Forwarding Messages via Socket.
NXLog will not have access to the facility and
severity codes because Rsyslog, by default, follows the BSD
Syslog convention of not writing the PRI code to the
By default, NXLog runs as user
nxlog and does not have permission to
read files in
/var/log. The simplest solution for this is to run NXLog
as root by omitting the
User option, but it is more secure to provide the
necessary permissions explicitly.
Check the user or group ownership of the files in
/var/logand configure if necessary. Some distributions use a group for the log files by default. On Debian/Ubuntu, for example, Rsyslog is configured to use the
admgroup. Otherwise, modify the Rsyslog configuration to use different ownership for log files as shown below./etc/rsyslog.conf or /etc/rsyslog.d/nxlog.conf
$FileOwner root $FileCreateMode 0640 $DirCreateMode 0755 $Umask 0022 # Default on Debian/Ubuntu $FileGroup adm # Or use the "nxlog" group directly #$FileGroup nxlog
Run NXLog under a user or group that has permission to read the log files. Either use a user or group directly with the
nxlog.conf, or add the
nxloguser to a group that has permission. For example, on Debian/Ubuntu add the
nxloguser to the
admgroup by running
usermod -a -G adm nxlog.
If necessary, fix permissions for any files NXLog will be reading from that already exist (use the correct group for your system).
# chgrp adm /var/log/messages # chmod g+r /var/log/messages
Configure NXLog to read from the required file(s) (see the example below). Then restart NXLog.
If the Rsyslog configuration has been modified, restart Rsyslog (
systemctl restart rsyslog).
With the following configuration, NXLog will read logs from
/var/log/messages, parse the events as Syslog, convert them to JSON, and
forward the plain JSON to another host via TCP.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 <Extension _json> Module xm_json </Extension> <Extension _syslog> Module xm_syslog </Extension> <Input in> Module im_file File '/var/log/messages' Exec parse_syslog(); </Input> <Output out> Module om_tcp Host 192.168.1.1 Port 1514 Exec $raw_event = to_json(); </Output>