Samba: Logging User Activity

Ever wondered why Samba seems to log so many things, except what you’re interested in? So did I, and it took me a while to find out that 1) there actually is a solution and 2) how to configure this. Here’s how.

The solution to logging what a user is actually doing can be achieved with Stackable VFS Modules, which is available since Samba 3. Unfortunately, the link there does not describe the full_audit module, which I highly recommend using instead of audit or extd_audit. The reason for this is that I couldn’t get those modules to log simple things like a file upload by a user, unless I chose VFS log level 10.

Using the Full_audit VFS Module

If you’re running Debian unstable like I do, then full_audit is included when installed from the APT. To find out which modules you have, take a look in /usr/lib/samba/vfs. When you’re sure you have the module, configure it as follows in smb.conf:

    vfs objects = full_audit

    full_audit:prefix = %u|%I|%m|%S
    full_audit:success = mkdir rename unlink rmdir pwrite
    full_audit:failure = none
    full_audit:facility = local7
    full_audit:priority = NOTICE

Let’s go through it one line at a time.

• vfs objects: we’d like to use the full_audit module.
• full_audit:prefix: Every line that full_audit outputs will be prefixed by this line, in which you can use Samba variables. This line will prefix the username, IP, machine name and share name, separated by pipes.
• full_audit:success: This specifies which actions will actually be logged when it has successfully been completed. unlink is in this case a delete action and pwrite is an upload action.
• full_audit:failure: Specifies which actions should be logged, but which have resulted in a failure. Since a failure will often mean that nothing has been changed, I found that it is not interesting to log any of these actions.
• full_audit:facility: By default, full_audit will only write to the system syslog, but you can specify a different ‘syslog facility’ to write all output to a different log file. Custom syslog facilities should be named local[number], where number is a number between 0 and 7 (don’t ask me why syslogd doesn’t support any name). I’ll get back on this later.
• full_audit:priority: This line sets the severity of the log messages that are generated, like ‘notice’, ‘info’, ‘warning’, ‘debug’, ‘alert’. There are probably more, but these are the most well-known ones.

Creating a Syslogd Facility

To specify a custom log file to which full_audit should write, you should create a new syslogd facility. A facility can be described in syslog.conf. Since I had chosen the facility local7, I can add that facility to the configuration like this:

local7.*                        /var/log/samba/log.audit

This line means that all log messages of facility local7 will be written to /var/log/samba/log.audit. The star is needed to say that I’d like to log messages of any severity to the same log file. Finally, restart the syslogd daemon: /etc/init.d/sysklogd restart


Final Words

• When things don’t seem to be working, ensure you have restarted/reloaded syslogd and samba.
• If there is anything bad you could say about full_audit, then it would be that it can’t output log messages to the log file specified in smb.conf. I always found it very useful that Samba could log by machine name by specifying log file = /var/log/samba/log.%m, but full_audit cannot use this. If you find a way though, please let me know!
• Other references: A blog in a language I can’t read where I took the configuration part from: Monitoring Aktivitas Samba

Output Example

Here is an example of what the configuration just explained generates:

Aug 10 11:52:52 rhino smbd_audit: moiristo|123.45.67.89|moiristo|moiristo|unlink|ok|public/Upload/hypnotoad.gif
Aug 10 11:52:59 rhino smbd_audit: moiristo|123.45.67.89|moiristo|moiristo|pwrite|ok|public/Upload/hypnotoad.gif
Aug 10 11:53:41 rhino smbd_audit: moiristo|123.45.67.89|moiristo|moiristo|rename|ok|public/Upload/hypnotoad.gif|public/Upload/hypnotoads.gif
Aug 10 11:53:51 rhino smbd_audit: moiristo|123.45.67.89|moiristo|moiristo|rename|ok|public/Upload/hypnotoads.gif|public/Upload/hypnotoad.gif

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~ by moiristo on August 10, 2009.