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What is Tracing?
"Tracing" is a new form of logging, introduced in the 1.3.1 ProFTPD release series.

Trace logging has the concept of multiple logging channels, each of which has its own log level. Layers and APIs within the ProFTPD source will tend to use their own channels. There is no limit to the number of different log channels that can be supported.

Within a channel, the assumption is that lower log levels indicate higher priority or importance. Or to look at it another way, the higher the log level for channel, the more noisy that log channel might be. The lowest log level is 1; there is no upper log level limit.

Why have this new form of logging, in addition to all the other kinds of logs (e.g. SystemLog, ExtendedLog, etc) that a proftpd daemon can currently produce? The usual SystemLog of proftpd debug logging, at a high DebugLevel, was becoming unreadable; it is difficult to find the tidbits of knowledge amidst the other messages in that file. By separating log messages into channels and levels, tracing gives the administrator a much finer-grained control over the logging, given them a way of focusing the logging more narrowly, so only the area of code of interest is logged.

Support for tracing is enabled by default. Use the --disable-trace configure option, when compiling ProFTPD, to disable all tracing support. I recommend that high-traffic production sites, which have no need for debug logging at this granularity, use the --disable-trace option.

Configuration Directives
There are two new configuration directives for tracing: TraceLog and Trace. Note that for tracing to be effective, these two directives, if used, must appear at the start of your proftpd.conf file, before any other directives.

The TraceLog directive specifies a filename to which to write the tracing log messages. For example:

  TraceLog /var/ftpd/trace.log

Once you have configured your TraceLog, you will use the Trace directive to control the verbosity of that log:

  Trace channel1:level1 channel2:level2 ...

  Trace command:5 response:8 timer:2 config:9

  Trace DEFAULT:10

• auth
• binding
• command
• config
• ctrls
• data
• delay
• dns
• dso
• encode
• error
• event
• facl
• fsio
• ident
• inet
• lock
• log
• module
• netacl
• netio
• pam
• pool
• regexp
• response
• scoreboard
• signal
• site
• timer
• var

  TraceLog /path/to/ftpd/trace.log
  Trace DEFAULT:10

If you want to look at the default trace channels except for a particular channel, use level 0 to effectively disable that channel. For example, to exclude the "fsio" channel but see the rest of the default channels, you would use:

  Trace DEFAULT:10 fsio:0

Note that there are trace channel names that are not part of the "DEFAULT" channel name list (e.g. "class"); any custom channel names, such as might be used by a third-party module, are also not covered in the "DEFAULT" list. For example, the mod_tls module may log to a "tls" channel. Any messages to that "tls" channel would not appear in the TraceLog file, using the above configuration. Instead, you would need to explicitly mention the "tls" channel, i.e.:

  TraceLog /path/to/ftpd/trace.log
  Trace DEFAULT:10 tls:10

Optional Trace Log Channels
In addition to the default trace log channels listed above, there are optional trace log channels:

• directory

  The "directory" log channel is used when the core engine attempts to find the closest matching <Directory> section for a path.

• fileperms

  The "fileperms" log channel is used whenever a user action involving the filesystem (e.g. opening/closing/writing/renaming/deleting files or directories) fails. This channel will log the relevant FTP command, user name, UID/GID, filesystem path, and the error.

Trace Log Format
Every log message in a TraceLog uses the following format:

  timestamp [process ID] <channel:level>: message

  Jan 16 17:15:58 [30583] <auth:6>: dispatching auth request "endgrent" to module mod_auth_unix

Runtime Tracing
If Controls support is enabled in your proftpd, and you are using the mod_ctrls_admin module, then you can also use the ftpdctl command to adjust the trace logging settings in the running proftpd, without needing to change your proftpd.conf file. See:

  doc/contrib/mod_ctrls_admin.html#trace

Here's a concrete example of how tuning the trace logging at runtime can be useful. You may need the extra information logged via trace logging in order to track down/debug some issue, but you do not want to enable trace logging all of the time in your environment. Fortunately, it is possible to make it possible to get the trace logging information you need, when you need to get it, and then turn the trace logging off all without restarting proftpd.

First, you need to configure your proftpd.conf like so:

  TraceLog /path/to/proftpd/trace.log
  Trace DEFAULT:0

  $ ftpdctl trace lock:10 scoreboard:5

  $ ftpdctl trace DEFAULT:0

Use Only When Needed
Remember that tracing is a verbose (and thus expensive) form of logging, and thus makes the proftpd daemon run slower. Tracing should only ever be used for debugging and development purposes; once your proftpd is up and running the way you need, you should remove all Trace and TraceLog directives from your proftpd.conf.

Frequently Asked Questions

Question: Can I configure Trace on a per-user basis, using mod_ifsession's <IfUser>?
Answer: You can indeed use mod_ifsession for Trace configurations, starting in ProFTPD 1.3.4rc1. To do this, you need to use the optional "session" keyword in your Trace configuration, e.g.:

  <IfUser traced-user>
    Trace session DEFAULT:10
  </IfUser>