rotating-log

Writable stream with an underlying rotating log file. The rotation is somewhat configurable (to become moreso), but defaults to rotating daily or once the size of the file >= 50MB, and only one rotated log file will be kept.

This is a simple module. It does not do compression or anything fancy, and could probably stand to have more error checking in place. It only exposes a writable stream interface and has no additional methods.

One feature (important to me), is that the log file is never moved/removed, and can be read from (via tail -f or whatever) indefinitely, even through rotations. When it comes time to rotate, output to the file is paused, the file is copied to the same name + '.1' (the existing '.1' is rotated to '.2' before-hand, etc), then the logfile is truncated in place, and finally logging is resumed. During this (relatively quick) process, log messages will be buffered in memory, which always carries a risk.

Install

npm install rotating-log

Example

var RotatingLog = require('rotating-log')
,   logfile     = '/tmp/rotating-log-demo.log'
,   log         = RotatingLog(logfile, {keep:2, maxsize:512}) // 512 byte cap

log.on('rotated', function () {
    console.log('The log file was rotated.')
})
log.on('error', function (err) {
    console.error('There was an error: %s', err.message || err)
})

setInterval(function () {
    log.write( (new Date).toString() + '\n' )
}, 1000)

console.log('Logging to %s', logfile)
console.log('execute "tail -f %s" to watch log. press ctrl-c to exit.', logfile)

Usage

RotatingLog(logfilepath, options)

• logfilepath (required) - path to the log file
• options (default: {}) - configurable behaviour options

Configuration Options

• keep (default:1) - number of rotated log files to keep; rotations beyond this number are removed
• maxsize (default:50MB) - maximum size of log file before rotation is forced (IN BYTES)

Supported Events

• rotating - Emitted once a rotation begins
• rotated - Emitted once a rotation has completed

Rotated Filenames

Rotated logfiles will be found in the same directory as the primary log file with an extra index appended to the filename. The higher the digit, the older the rotated logfile (this is identical to traditional unix logging). For example, the following command:

var log = new RotatingLog('/tmp/test.log', {keep:3})

Will result in the following files (after a couple of days):

test.log
test.log.1
test.log.2
test.log.3

The next time the log is rotated, test.log.3 will be removed, test.log.2 will become test.log.3, test.log.1 will become test.log.2, and test.log will become test.log.1. Afterwards, test.log is truncated.

Testing

npm test