15.1. What is “journald”?¶
Journald is a system for collecting logs and data from devices running “systemd”. Many distributions have moved away standard syslog services in favor of “journald”. The concept is to replace standard “text” base logging for a more “database” binary logging approach.
While this method has advantages, there are several limitations. Software like “Sagan” doesn’t natively
read “journald” files. Journald also lacks the ability to send logs to a remote host. Journald relies on
rsyslog to send logs to a remote host. While there are some methods
to send logs to a remote host via Journald, most are not mature and more of a “proof of concept”
than a solution. This makes using a service like
rsyslog the best method to send
logs generated by Journald.
15.2. Analyzing journald logs locally¶
Using the “Journald” command
journalctl, it is possible to create a JSON stream representing Journald
data. Using Sagan built in JSON processing, it is possible to analyze this data. As Journald writes
log data, the
journalctl converts it to JSON and sends it to
stdout. This can be redirected to
a named pipe (FIFO). For example,
journalctl -f -o json > /var/sagan/fifo/journald.fifo will direct
log data to a named pipe which Sagan can read. Within the Sagan configuration file, you would want to
set the following options:
input-type: json # pipe or json json-map: "$RULE_PATH/json-input.map" # mapping file if input-type: json json-software: journald # by "software" type.
15.3. Analyzing journald logs remotely¶
In situations where
rsyslog is not an option, you can using
journalctl to send
logs to a remote host in raw JSON. For example,
journalctl -f -o json | nc 192.168.1.1 1514. This
netcat to send logs to 192.168.1.1 on port 1514. Your receiver would need to be configuration
to accepts incoming connection and date in a __raw__ format (non-syslog). Sagan could then be used
on the receiving side to analyze data from various devices. You would likely want to wrap the “journalctl”
in a script and infinite loop so
journalctl will automatically restart if the TCP log connection is broken.