Does python logging.handlers.RotatingFileHandler allow creation of a group writable log file?

Question

I’m using the standard python (2.5.2) logging module, specifically the RotatingFileHandler, on a linux system. My application supports both a command-line interface and a web-service interface. I would like to have both write to the same log file. However, when the log file gets rotated, the new file has 644 permissions and is owned by the web server user which prevents the command-line user from writing to it. Can I specify that new log files should be group-writable in the logging configuration or during logging initialization?

I have looked into the mode setting (r/w/a), but it doesn’t seem to support any file permissions.

Asked By: Cory Engebretson

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Source

Answer 1

I resorted to scanning the logging.handlers module and was unable to see any way to specify a different file permissions mode. So, I have a solution now based on extending the RotatingFileHandler as a custom handler. It was fairly painless, once I found some nice references to creating one. The code for the custom handler is below.

class GroupWriteRotatingFileHandler(handlers.RotatingFileHandler):

    def doRollover(self):
        """
        Override base class method to make the new log file group writable.
        """
        # Rotate the file first.
        handlers.RotatingFileHandler.doRollover(self)

        # Add group write to the current permissions.
        currMode = os.stat(self.baseFilename).st_mode
        os.chmod(self.baseFilename, currMode | stat.S_IWGRP)

I also discovered that to reference the custom handler from a logging config file, I had to bind my module to the logging namespace. Simple to do, but annoying.

from mynamespace.logging import custom_handlers
logging.custom_handlers = custom_handlers

References I found useful:
binding custom handlers and
creating custom handlers

Answered By: Cory Engebretson

Answer 2

Here is a slightly better solution. this overrides the _open method that is used. setting the umask before creating then returning it back to what it was.

class GroupWriteRotatingFileHandler(logging.handlers.RotatingFileHandler):    
    def _open(self):
        prevumask=os.umask(0o002)
        #os.fdopen(os.open('/path/to/file', os.O_WRONLY, 0600))
        rtv=logging.handlers.RotatingFileHandler._open(self)
        os.umask(prevumask)
        return rtv

Answered By: rob

Answer 3

James Gardner has written a handler that only rotates files, not creating or deleting them:
http://packages.python.org/logrotate/index.html

Answered By: tobych

Answer 4

$ chgrp loggroup logdir
$ chmod g+w logdir
$ chmod g+s logdir
$ usermod -a -G loggroup myuser
$ umask 0002

Answered By: wcc526

Answer 5

Here’s a complete solution for Django based on rob‘s solution. in my_module :

import logging
import logging.handlers
import os

The class= that happens during the logging configuration is evaluated in the namespace of the logging module, and by default this does not have a binding to handlers. So we have to put it in explicitly before we can extend it. See this SO article

logging.handlers = logging.handlers

It’s this magical incantation that took me forever to find – I couldn’t believe it did anything! Finally, Jon’s class will load without errors.

class GroupWriteRotatingFileHandler(logging.handlers.RotatingFileHandler):    
    def _open(self):
        prevumask = os.umask(0o002)
        rtv = logging.handlers.RotatingFileHandler._open(self)
        os.umask(prevumask)
        return rtv

To use this for Django add the following this in the settings file

from my_module import GroupWriteRotatingFileHandler
logging.handlers.GroupWriteRotatingFileHandler = GroupWriteRotatingFileHandler

And then in LOGGING['handlers']['file'] you have

'class': 'logging.handlers.GroupWriteRotatingFileHandler'

Answered By: gluejar

Answer 6

Here is a simple solution worked fine:

import os

class GroupWriteRotatingFileHandler(handlers.RotatingFileHandler):
    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)
        os.chmod(self.baseFilename, 0o0777)  # You can change whatever permission you want here.

        # you can also change the group of the file:
        os.chown(self.baseFilename, uid, gid)   # pass the user_id and group_id you want to set

Answered By: DennisLi

Answer 7

It looks that def _open(self): worked with umask(0o000) to get all the permissions of -rw-rw-rw-.

os.chmod(self.baseFilename, 0o0777) failed with ValueError: Unable to configure handler 'some_handler': [Errno 1] Operation not permitted: if the log file has ownership of root:root that’s different from running process’s, such as testuser.

from logging import handlers

import logging
import os

class GroupWriteRotatingFileHandler(handlers.RotatingFileHandler):
    def _open(self):
        prevumask = os.umask(0o000)  # -rw-rw-rw-
        rtv = logging.handlers.RotatingFileHandler._open(self)
        os.umask(prevumask)
        return rtv

LOGGING = {
    'handlers': {
        'db_handler': {
                'level': 'DEBUG',
                'class': 'log.GroupWriteRotatingFileHandler',
                'filename': PATH_TO_LOGS + '/db.log',
                'maxBytes': maxBytes,
                'backupCount': backupCount,
                'formatter': 'standard',
        },

Log files:

logs]# ls -lrt
-rw-rw-rw- 1 root root 71 Apr  1 16:02 db.log

logs]# ls -lrt
total 0
-rw-rw-rw- 1 testuser testuser 0 Apr  1 16:20 db.log

Answered By: caot

Answer 8

I think what described here is an anti-pattern – different processes should not write data into the same file.

And non of the solutions above worked for me, causing different permissions issues in different scenarios.

As a temp workaround I’ve added a random suffix into the log filename so each process will get a unique filename on a startup.

The proper way to solve this issue – have a centralized log handler (log server), e.g. rsyslog.

Answered By: ARA1307

Does python logging.handlers.RotatingFileHandler allow creation of a group writable log file?

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