ProFTPD mini-HOWTO - Logging

## Logging

Logging
Logging the activity of the server is an integral part of effective server administration. ProFTPD provides several different and flexing logging mechanisms. When examining the different logging mechanisms, have in mind the intended use of the logged data, the volume, any post-processing that may need to be done, etc. Log files are more useful when they contain a complete record of server activity. It is often easier to simply post-process the log files to remove requests that you do not want to consider.

Security Warning
Anyone who can write to the directory where ProFTPD is writing a log file can almost certainly gain access to the UID that the server is started under, which is normally `root`. Do not give people write access to the directory where the logs are stored without being aware of the consequences: if the logs directory is writable (by a non-`root` user), someone could replace a log file with a symlink to some other system file, and then `root` might overwrite that file with arbitrary data. If the log files themselves are writable (by a non-`root` user), then someone may be able to overwrite the log itself with bogus data.

When opening log files, `proftpd` will by default log a warning if the file being opened for logging is in a directory that does not exist, or is world-writable. The log file will not be written in world-writable directories; there are no exceptions. (If you have configured log files in your `proftpd.conf` that are not appearing, check for the warnings about world-writable directories.) The `proftpd` process will also, by default, log a warning if the file given is a symlink; this symlink check can be configured via the `AllowLogSymlinks` directive.

In addition, log files may contain information supplied directly by the client, without escaping. Therefore, it is possible for malicious clients to insert control-characters in the log files, so care must be taken in dealing with raw logs.

`syslog`
By default, `proftpd` will log via `syslog(3)`, using the `daemon` facility (`auth` for some logging), at various levels: `err`, `notice`, `warn`, `info`, and `debug` (debugging is done at this syslog level). The location of the server's log files in this case is determined by your `/etc/syslog.conf` configuration.

`Log Files`
There are three main types of logs that a `proftpd` daemon can generate: `TransferLog`s, a `SystemLog`, and `ExtendedLog`s.

A `TransferLog` is the most common log kept, recording file transfers. Its format is described in the `xferlog(5)` man page, also available here

If the site administrator wants to have `proftpd` log its messages to a file rather than going through `syslogd`, the `SystemLog` configuration directive is the one to use. There is only one such file kept for the entire daemon. See the `ServerLog` directive for keeping a similar log on a per-vhost basis.

The ExtendedLog directive is used to create log files of a very flexible and configurable format, and to have granular control over what is logged, and when. The format of an `ExtendedLog` is described using the LogFormat directive. Multiple `ExtendedLogs` can be configured, each with a different format.

Log Analysis
There are a variety of log analyzers available; these are just a few:

- Webalizer: http://www.webalizer.org/
- HTTP-analyze: http://www.netstore.de/Supply/http-analyze/
- Analog: http://www.analog.cx/
- Report Magic: http://www.reportmagic.org/
- FTPWeblog: http://www.nihongo.org/snowhare/utilities/ftpweblog/

Log Rotation
On even a moderately busy server, the quantity of information stored in the log files is very large. It will consequently be necessary to periodically rotate the log files by moving or deleting the existing logs. This cannot be done while the server is running, because the daemon will continue writing to the old log file as long as it holds the file open. Instead, the server must be restarted after the log files are moved or deleted so that it will open new log files.

Another way to perform log rotation is using FIFOs as discussed in the next section.

FIFOs (a.k.a. named pipes)
ProFTPD is capable of writing log files to FIFOs, from which another process can read. Use of this capability dramatically increases the flexibility of logging, without adding code to the main server. In order to write logs to a pipe, simply create the FIFO at the desired path (`man mkfifo(1)`), and use that path in the logging configuration directive.

One important use of piped logs is to allow log rotation without having to restart the server. One such popular flexible log rotation program is cronolog; however, at present cronolog requires a small patch to enable it to read from a FIFO (by default, cronolog reads data from stdin). Please contact the author of this article for details concerning the patch.

Here's an example of FIFO-based logging script, based on one posted by Michael Renner:

      #!/usr/bin/perl

      use strict;

      use File::Basename qw(basename);
      use Sys::Syslog qw(:DEFAULT setlogsock);

      my $program = basename($0);

      my $fifo = '/var/log/proftpd-log.fifo';
      my $syslog_facility = 'daemon';
      my $syslog_level = 'info';

      open(FIFO, "< $fifo") or die "$program: unable to open $fifo: $!\n";

      setlogsock 'unix';

      openlog($program, 'pid', $syslog_facility);
      syslog($syslog_level, $_) while (<FIFO>);
      closelog();

      close(FIFO);
      exit 0;

More complex filtering can be added to such scripts.

If using FIFOs, there are some caveats to keep in mind. If you use in `init.d` script to start `standalone` daemons, you can add commands to start the FIFO logging programs first, before the daemon. For `inetd`-run servers, consider wrapping up the necessary commands for starting a FIFO reader and the server into a simple shell script, or simply run the FIFO-reading program from an `init.d` script, and save the overhead of starting that process, in addition to the `proftpd` process, for each FTP session.

FIFO-based log readers are a very powerful tool, but they should not be used where a simpler solution like off-line post-processing is available.

Note: In ProFTPD 1.3.3, the code was changed to use nonblocking `open(2)` system calls when opening log files. This was done to prevent a `proftpd` process from blocking indefinitely (i.e. "hanging") if the log file was a FIFO, and there was no FIFO reader process running when the log file was opened. However, some sites do want this blocking open behavior, as their FIFO reader processes may be temporarily busy. To get the pre-1.3.3 blocking behavior, you will need to compile proftpd using the `--disable-nonblocking-log-open` configure option.

SQL Logging
The `mod_sql` module also enables some powerful and complex logging capabilities...

Pid File
On startup, `proftpd` saves the process ID of the parent daemon process to the file `var/proftpd/proftpd.pid`. This filename can be changed with the PidFile directive. The process ID (aka PID) is for use by the administrator in restarting and terminating the daemon by sending signals to the parent process. For more information see the stopping and starting page.

Scoreboard File
The last type of "logging" is done via the scoreboard file. The scoreboard is binary-formatted file the server uses to store information about each session; it is this file that is read by `ftptop`, `ftpwho` and `ftpcount`. The location for the scoreboard file is determined by the `ScoreboardFile` directive.

Frequently Asked Questions

Question: How can I direct the `TransferLog` logging to syslog?
Answer: It is not currently possible to configure proftpd to log `TransferLog` data to syslog. However, you can configure an `ExtendedLog` which logs to syslog, and which uses a `LogFormat` to log the data you wish. For example:

      LogFormat xfer "%h %l %u %t\"%r\" %s %b"
      ExtendedLog syslog:notice xfer

tells proftpd to log that `LogFormat` via syslog at the "notice" syslog level.

Last Updated: $Date: 2010/04/19 20:10:35 $