# Logging¶

Kubos Linux uses rsyslog to automatically route log messages to the appropriate log file and then rotate those files when they become too large.

## Default Behavior¶

Two logging policy files are included in /etc/rsyslog.d/:

• kubos-apps.conf - Specifies the logging and rotation policies for mission applications
• kubos-services.conf - Specifies the logging and rotation policies for services

Within those files, and the main /etc/rsyslog.conf file which controls other system logs, each policy has the following format:

$outchannel {policy_name},/var/log/{destination_file},{max_size},{log_rotation_script} {facility}.{priority} :omfile:${policy_name}


An example policy looks like this:

$outchannel service_debug,/var/log/kubos-debug.log,100000,/home/system/kubos/log-rotate.sh kubos-debug.log daemon.debug :omfile:$service_debug


Any of these components may be updated within their respective files in order to change the policy to match the user’s desired behavior.

### Log Creation¶

Log files are traditionally stored in /var/log.

/var/log has been set up as a symlink to /home/system/log. This way log files reside in permanent storage and will be preserved through OS upgrades.

Messages written using the daemon facility will be routed to files with the naming scheme kubos-*.log. This facility is used by all Kubos services.

Messages written using the user facility will be routed to files with the naming scheme app-*.log. This facility should be used by all mission applications.

For each of these naming schemes, the following files may be created:

• *-debug.log - Records all log messages
• *-info.log - Records log messages with a priority of info or higher
• *-warn.log - Records log messages with a priority of warn or higher

### Log Rotation¶

The /home/system/kubos/log-rotate.sh script is used to execute the rotation behavior.

By default, all debug log files have a maximum size of 100KB and all other log files have a maximum size of 10KB. This value can be updated by changing the max size parameter of the appropriate logging policy.

Once this size is reached, the current file is renamed as an archive file and a new log file is started. Archive files use their original name, but are suffixed with the current timestamp. For example, kubos-debug.log.2018.12.01-00.12.07.

By default, nine archive files of each log type will be retained. If a new archive file is created and there are already five files, the oldest will be deleted. This value is controlled by the MAX_COUNT variable in the log-rotate.sh script.

## Examples¶

The following examples show how to set up and use the logging capabilities.

### Rust¶

Rust programs will use the standard log framework crate in conjunction with a crate capable of writing syslog messages. For example, using syslog:

use log::{debug, error};

use failure::{Error, SyncFailure};
use syslog::Facility;

fn main() -> Result<(), Error> {
if let Err(error) = syslog::init(
// Log using the User facility (Kubos services will use LOG_DAEMON)
Facility::LOG_USER,
// Set the minimum log level we care about
log::LevelFilter::Debug,
// Set the application/program name
Some("log-test"),
// Have to do map_err(SyncFailure::new) in order to convert
// error-chain Error into something failure can handle
).map_err(SyncFailure::new)
{
eprintln!("Failed to start logging: {}", error);
}

debug!("this is a debug {}", "message");
error!("this is an error!");
Ok(())
}


### Python¶

Python programs will import two things: the main logging library and the SysLogHandler log handler.

import logging
from logging.handlers import SysLogHandler

# Create a new logger. The name here is unimportant
logger = logging.getLogger('log-test')
logger.setLevel(logging.DEBUG)

# We'll send our messages to the standard Unix domain socket for logging.
# Since this is a user program, we'll use the LOG_USER facility
handler = SysLogHandler(address='/dev/log', facility=SysLogHandler.LOG_USER)

# Prefix all messages with the application name so that SysLog will set the
# programname and APP-NAME property values accordingly, allowing us to filter
# by application, if we so choose
formatter = logging.Formatter('log-test: %(message)s')

handler.formatter = formatter