Standard Log Format for PantherX Applications

Since PantherX Devices are spread all over the world, we have to define facilities for trace issues remotely. having a unified log format could help us to trace and debug this issues faster and easier.

In this document we define a standard way to unify PantherX Application log creation and storage.


syslog is a standard for message logging. it allows separation between the software that generates log messages, system that stores them and the the software that reports and analyze them (wikipedia).

syslog is the main logging facility in most Operating systems including GNU/Linux, BSDs and Mac Os, so we decided to use syslog as our log storage service for PantherX.

by default, GuixSD configured syslog to log anything (except mail) of level info or higher to /var/log/messages. if we need debug level logs as well, we should access /var/log/debug file. all mail related logs are also stored in /var/log/maillog.

Log Message Format

In order to have a meaningful log file to be useful in later use, we need to specify a series of rules to follow for our log messages. following these rules could help us understand and fix issues faster and easier.

Message format rules

  1. Log Messages need to specify exact location of message in code.
  2. Since syslog doesn't support log level grouping, so we need to specify log levels internally inside our submitted messages.
  3. Avoid multiline logs, since they often get split up on the way to the log collector.
  4. ... [this list needs to be completed] ...

Log New Messages

syslog has libraries for many programming languages, since most of PantherX Applications are based on C++ and Python we only cover these two:

Syslog usage in C++

in order to have syslog enabled in C++ applications we need to include <syslog.h> header file. first of all we need initiate logger with openlog method. submit logs using syslog method and close our logger using closelog method. here is a short description about syslog related methods:

Open connection to a Syslog service

we need to (re)open a connection to syslog service, prior to submit log messages using openlog method. more info

void openlog (const char *ident, int  option, int  facility)
  • *ident: string that identifies the current log component, this could be name of application that submits the log messages.
  • option: mask variable that holds options about how logs should submit to syslog service.
Option Description
LOG_CONS Write directly to system console if there is an error while sending to system logger.
LOG_NDELAY Open the connection immediately
LOG_NOWAIT Don't wait for child processes that may have been created while logging the message.
LOG_ODELAY Opening of the connection is delayed until syslog() is called.
LOG_PERROR (Not in POSIX.1-2001 or POSIX.1-2008.) Print to stderr as well.
LOG_PID Include PID with each message.
  • facility: pointed to the default facility that log messages should submit to
Facility Description
LOG_AUTH security/authorization messages
LOG_AUTHPRIV security/authorization messages (private)
LOG_CRON clock daemon (cron and at)
LOG_DAEMON system daemons without separate facility value
LOG_FTP ftp daemon
LOG_KERN kernel messages (these can't be generated from user processes)
LOG_LOCAL0 through LOG_LOCAL7 reserved for local use
LOG_LPR line printer subsystem
LOG_MAIL mail subsystem
LOG_NEWS USENET news subsystem
LOG_SYSLOG messages generated internally by syslogd
LOG_USER (default) generic user-level messages
LOG_UUCP UUCP subsystem

Submit Log Messages

in order to submit a new message, we need use syslog method . more info

void syslog (int  facility_priority, const char *format, )
void vsyslog (int  facility_priority, const char *format, va_list  arglist)
  • facility_priority: indicates the facility and priority which the log message should submitted to. LOG_MAKEPRI(facility, priority) macro is used to create proper value for this parameter.
Log Level Description
LOG_EMERG system is unusable
LOG_ALERT action must be taken immediately
LOG_CRIT critical conditions
LOG_ERR error conditions
LOG_WARNING warning conditions
LOG_NOTICE normal, but significant, condition
LOG_INFO informational message
LOG_DEBUG debug-level message
  • format: log message format string
  • ...: log message format arguments
  • arglist: variable list specified as format arguments

Close Connection to Syslog service

close already opened connection to syslog service using closelog method. more info

void closelog (void)

Provide Mask about logs the we want to ignore for send

in order to reduce the amount of log messages that we send to syslog service, we can set a default mask to ignore them locally using setlogmask method. this could be used to reduce the amount of submitted logs in Production mode in comparison to Debug mode. more info

int setlogmask (int  mask)
  • mask: integer value indicating about logs that need to be uploaded to syslog.
    • we need to use LOG_MASK macro to specify various log levels: LOG_MASK(LOG_EMERG) | LOG_MASK(LOG_ERROR)
    • alternatively we could use LOG_UPTO macro to ignore levels greater than specified level: LOG_UPTO(LOG_WARNING)

syslog usage in Python

in order to use syslog inside python scripts we need to import syslog module to our code. similar to C++ usage, first we need to initiate our syslog client using openlog method, send log messages using syslog method and close our logger client using closelog method. reference

Open Syslog connection

we need to open connection to syslog service using openlog method:

syslog.openlog([ident[,  logoption[,  facility]]])
  • ident: optional param that prepends to every messages. default value for this parameter is sys.argv[0]
  • logoption: similar to C++ definition, this parameter holds bitwise mask for syslog connection
  • facility: default facility that logs should send to

Send Log Messages

in order to send log messages to syslog service, we need to use syslog method:

syslog.syslog(priority, message)
  • priority: bitwise mask for level and facility of message we want to send
  • message: string message that we want to send

Close Logger

in order to close already opened syslog connection, we use closelog method:


Provide Mask for log levels to ignore

Similar to C++ definition if we want to reduce the amount of log messages that we send to syslog service, we can set a default mask to ignore them locally using setlogmask method.

  • mask: indicates maximum level of logs that need to be uploaded to syslog.
    • LOG_MASK method is used to specify various log levels.
    • LOG_UPTO method is used to ignore levels greater than specified level.

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Last update: 2020-02-19 21:18:01 +0000

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