# `syslog` — Unix syslog library routines

This module provides an interface to the Unix `syslog` library routines. Refer to the Unix manual pages for a detailed description of the `syslog` facility.

Availability: Unix, not Emscripten, not WASI.

This module wraps the system `syslog` family of routines. A pure Python library that can speak to a syslog server is available in the `logging.handlers` module as `SysLogHandler`.

The module defines the following functions:

syslog.syslog(message)
syslog.syslog(priority, message)

  Send the string message to the system logger. A trailing newline is added if necessary. Each message is tagged with a priority composed of a facility and a level. The optional priority argument, which defaults to `LOG_INFO`, determines the message priority. If the facility is not encoded in priority using logical-or (`LOG_INFO | LOG_USER`), the value given in the `openlog()` call is used.

  If `openlog()` has not been called prior to the call to `syslog()`, `openlog()` will be called with no arguments.

  Raises an auditing event `syslog.syslog` with arguments `priority`, `message`.

  Changed in version 3.2: In previous versions, `openlog()` would not be called automatically if it wasn’t called prior to the call to `syslog()`, deferring to the syslog implementation to call `openlog()`.

  Changed in version 3.12: This function is restricted in subinterpreters. (Only code that runs in multiple interpreters is affected and the restriction is not relevant for most users.) `openlog()` must be called in the main interpreter before `syslog()` may be used in a subinterpreter. Otherwise it will raise `RuntimeError`.

syslog.openlog([ident[, logoption[, facility]]])

  Logging options of subsequent `syslog()` calls can be set by calling `openlog()`. `syslog()` will call `openlog()` with no arguments if the log is not currently open.

  The optional ident keyword argument is a string which is prepended to every message, and defaults to `sys.argv[0]` with leading path components stripped. The optional logoption keyword argument (default is 0) is a bit field – see below for possible values to combine. The optional facility keyword argument (default is `LOG_USER`) sets the default facility for messages which do not have a facility explicitly encoded.

  Raises an auditing event `syslog.openlog` with arguments `ident`, `logoption`, `facility`.

  Changed in version 3.2: In previous versions, keyword arguments were not allowed, and ident was required.

  Changed in version 3.12: This function is restricted in subinterpreters. (Only code that runs in multiple interpreters is affected and the restriction is not relevant for most users.) This may only be called in the main interpreter. It will raise `RuntimeError` if called in a subinterpreter.

syslog.closelog()

  Reset the syslog module values and call the system library `closelog()`.

  This causes the module to behave as it does when initially imported. For example, `openlog()` will be called on the first `syslog()` call (if `openlog()` hasn’t already been called), and ident and other `openlog()` parameters are reset to defaults.

  Raises an auditing event `syslog.closelog` with no arguments.

  Changed in version 3.12: This function is restricted in subinterpreters. (Only code that runs in multiple interpreters is affected and the restriction is not relevant for most users.) This may only be called in the main interpreter. It will raise `RuntimeError` if called in a subinterpreter.

syslog.setlogmask(maskpri)

  Set the priority mask to maskpri and return the previous mask value. Calls to `syslog()` with a priority level not set in maskpri are ignored. The default is to log all priorities. The function `LOG_MASK(pri)` calculates the mask for the individual priority pri. The function `LOG_UPTO(pri)` calculates the mask for all priorities up to and including pri.

  Raises an auditing event `syslog.setlogmask` with argument `maskpri`.

The module defines the following constants:

Priority levels (high to low):

  `LOG_EMERG`, `LOG_ALERT`, `LOG_CRIT`, `LOG_ERR`, `LOG_WARNING`, `LOG_NOTICE`, `LOG_INFO`, `LOG_DEBUG`.

Facilities:

  `LOG_KERN`, `LOG_USER`, `LOG_MAIL`, `LOG_DAEMON`, `LOG_AUTH`, `LOG_LPR`, `LOG_NEWS`, `LOG_UUCP`, `LOG_CRON`, `LOG_SYSLOG`, `LOG_LOCAL0` to `LOG_LOCAL7`, and, if defined in `<syslog.h>`, `LOG_AUTHPRIV`.

Log options:

  `LOG_PID`, `LOG_CONS`, `LOG_NDELAY`, and, if defined in `<syslog.h>`, `LOG_ODELAY`, `LOG_NOWAIT`, and `LOG_PERROR`.

## Examples

### Simple example

A simple set of examples:

    import syslog

    syslog.syslog('Processing started')
    if error:
        syslog.syslog(syslog.LOG_ERR, 'Processing started')

An example of setting some log options, these would include the process ID in logged messages, and write the messages to the destination facility used for mail logging:

    syslog.openlog(logoption=syslog.LOG_PID, facility=syslog.LOG_MAIL)
    syslog.syslog('E-mail processing initiated...')