Syslog Monitor

The Syslog monitor allows the Scalyr Agent to act as a syslog server, proxying logs from any application or device that supports syslog. It can recieve log messages via the syslog TCP or syslog UDP protocols.

An agent monitor plugin is a component of the Scalyr Agent. To use a plugin, simply add it to the monitors section of the Scalyr Agent configuration file (/etc/scalyr/agent.json). For more information, see Agent Plugins.

Sample Configuration

This sample will configure the agent to accept syslog messages on TCP port 601 and UDP port 514, from localhost only:

monitors: [
    module:                    "scalyr_agent.builtin_monitors.syslog_monitor",
    protocols:                 "tcp:601, udp:514",
    accept_remote_connections: false

You can specify any number of protocol/port combinations. Note that on Linux, to use port numbers 1024 or lower, the agent must be running as root.

You may wish to accept syslog connections from other devices on the network, such as a firewall or router which exports logs via syslog. Set accept_remote_connections to true to allow this.

Additional options are documented in the Configuration Reference section, below.

Log files and parsers

By default, all syslog messages are written to a single log file, named agentSyslog.log. You can use the message_log option to specify a different file name (see Configuration Reference).

If you'd like to send messages from different devices to different log files, you can include multiple syslog_monitor stanzas in your configuration file. Specify a different message_log for each monitor, and have each listen on a different port number. Then configure each device to send to the appropriate port.

syslog_monitor logs use a parser named agentSyslog. To set up parsing for your syslog messages, go to the Parser Setup Page and click one of the action buttons for the agentSyslog parser, such as Ask us to create for you. If you are using multiple syslog_monitor stanzas, you can specify a different parser for each one, using the parser option.

Sending messages via syslog

To send messages to the Scalyr Agent using the syslog protocol, you must configure your application or network device. The documentation for your application or device should include instructions. We'll be happy to help out; please drop us a line at


To send messages from another Linux host, you may wish to use the popular rsyslogd utility. rsyslogd has a powerful configuration language, and can be used to forward all logs or only a selected set of logs.

Here is a simple example. Suppose you have configured Scalyr's Syslog Monitor to listen on TCP port 601, and you wish to use rsyslogd on the local host to upload system log messages of type authpriv. You would add the following lines to your rsyslogd configuration, which is typically in /etc/rsyslogd.conf:

# Send all authpriv messasges to Scalyr.
authpriv.*                                              @@localhost:601

Make sure that this line comes before any other filters that could match the authpriv messages. The @@ prefix specifies TCP.

Viewing Data

Messages uploaded by the Syslog Monitor will appear as an independent log file on the host where the agent is running. You can find this log file in the Overview page. By default, the file is named "agentSyslog.log".

Docker mode

This plugin is also used to receive logs from Docker containers running on the local host in conjunction with the docker_monitor. See the Docker related options below for more details. When the monitor is used in Docker mode, it will write the logs to individual log files organized by containers.

Configuration Reference

Option Usage
module Always scalyr_agent.builtin_monitors.syslog_monitor
protocols Optional (defaults to tcp:601). Lists the protocols and ports on which the agent will accept messages. You can include one or more entries, separated by commas. Each entry must be of the form tcp:NNN or udp:NNN. Port numbers are optional, defaulting to 601 for TCP and 514 for UDP
accept_remote_connections Optional (defaults to false). If true, the plugin will accept network connections from any host; otherwise, it will only accept connections from localhost.
message_log Optional (defaults to agent_syslog.log). Specifies the file name under which syslog messages are stored. The file will be placed in the default Scalyr log directory, unless it is an absolute path
parser Optional (defaults to agentSyslog). Defines the parser name associated with the log file
tcp_buffer_size Optional (defaults to 8K). The maximum buffer size for a single TCP syslog message. Note: RFC 5425 (syslog over TCP/TLS) says syslog receivers MUST be able to support messages at least 2048 bytes long, and recommends they SHOULD support messages up to 8192 bytes long.
max_log_size Optional (defaults to 50 MB). How large the log file will grow before it is rotated. Set to zero for infinite size. Note that rotation is not visible in Scalyr; it is only relevant for managing disk space on the host running the agent. However, a very small limit could cause logs to be dropped if there is a temporary network outage and the log overflows before it can be sent to Scalyr
max_log_rotations Optional (defaults to 2). The maximum number of log rotations before older log files are deleted. Set to zero for infinite rotations.
log_flush_delay Optional (defaults to 1.0). The time to wait in seconds between flushing the log file containing the syslog messages.
mode Optional (defaults to "syslog"). If set to docker, the plugin will enable extra functionality to properly receive log lines sent via the `docker_monitor`. In particular, the plugin will check for container ids in the tags of the incoming lines and create log files based on their container names.
docker_regex Regular expression for parsing out docker logs from a syslog message when the tag sent to syslog only has the container id. If a message matches this regex then everything after the full matching expression will be logged to a file based on the docker_logfile_template option.
docker_regex_full Regular expression for parsing out docker logs from a syslog message when the tag sent to syslog included both the container name and id. If a message matches this regex then everything after the full matching expression will be logged to a file based on the docker_logfile_template option
docker_expire_log Optional (defaults to 300). The number of seconds of inactivity from a specific container before the log file is removed. The log will be created again if a new message comes in from the container
docker_accept_ips Optional. A list of ip addresses to accept connections from if being run in a docker container. Defaults to a list with the ip address of the default docker bridge gateway. If accept_remote_connections is true, this option does nothing.
docker_api_socket Optional (defaults to /var/scalyr/docker.sock). Defines the unix socket used to communicate with the docker API. This is only used when `mode` is set to `docker` to look up container names by their ids. WARNING, you must also set the `api_socket` configuration option in the docker monitor to this same value. Note: You need to map the host's /run/docker.sock to the same value as specified here, using the -v parameter, e.g. docker run -v /var/run/docker.sock:/var/scalyr/docker.sock ...
docker_api_version Optional (defaults to 'auto'). The version of the Docker API to use when communicating to docker. WARNING, you must also set the `docker_api_version` configuration option in the docker monitor to this same value.
docker_logfile_template Optional (defaults to containers/${CNAME}.log). The template used to create the log file paths for docker logs sent by other containers via syslog. The variables $CNAME and $CID will be substituted with the name and id of the container that is emitting the logs. If the path is not absolute, then it is assumed to be relative to the main Scalyr Agent log directory.
docker_cid_cache_lifetime_secs Optional (defaults to 300). Controls the docker id to container name cache expiration. After this number of seconds of inactivity, the cache entry will be evicted.
docker_cid_clean_time_secs Optional (defaults to 5.0). The number seconds to wait between cleaning the docker id to container name cache.